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									                                    BATTERIES AND CONVERTERS

Date: Fri, 05 Dec 1997 09:53:10 -0500
From: Patrick Flowers <>
Subject: Re: GMC: GMC Motorhome Battery Cutout

john nepper, jr. wrote:
> I have a problem with the auxiliary battery in my '76 Palm Beach. It seems to drain itself after only a week or
so... After several "dective" tries I've decided to just put a shutoff switch on the battery while it's in storage.
> Problem: The switch I bought says to install it on the negative side of the circut, is there any reason not to put
it on the positive side?


You didn't say what type of switch it was, but many of these are a bare knife switch. By putting it on the
negative side of the battery, if anything conductive touches the switch and gets grounded, it will not cause a
problem. If the above occurs with the switch mounted on the positive side, the best outcome will be a nasty
spark and an ensuing fire would be very likely.

Your problem is "parasitic" drain on the electric system. In the GMC's, this is usually a result of added "extras".
Sound systems seem to be the worst culprits. You didn't outline what type of detective work you did, but the
best approach is to turn everyting off and unplug everything you can from the 12V system. Next remove all the
fuses(be sure to label each one or you'll have lots of fun getting them all back in the right slots) and disconnect
the negative cables on both the motor and aux batteries. Connect an ammeter between the aux battery and
negative cable. Hopefully, it will read zero. If not, then you probably have a short somewhere between the
battery and the fuse panel (or someones tapped onto the cable before the fuse panel - it happens). Then insert
and remove one fuse at a time noting which ones result in a reading on the ammeter. That will tell you which
circuits are causing the problem. Once you know which circuit the culprit's on, you can disconnect the
accessories on those circuits one at a time, noting the change in indication on the ammeter.

This is a long process and may be more trouble than it's worth since you've already decided to install the

Hope this helps,

Date: Tue, 27 Jan 1998 08:07:35 -0500
From: Ralph Edelbach <>
Subject: GMC: Battery info?

Took the "new" '74 26 foot Glacier out for a short test run last Saturday, the sun was out for a while in NJ, and
when it stalled at a stop sign, the battery could not spin the engine fast enough to get it restarted. Even with the
switch in the "boost" position, it wasn't sufficient so a quick call to my wife who arrived and, after hooking up
the jumper cables, the mighty 455 roared back into life. Time to replace one or more batteries I suppose.

My question pertains to whether it is necessary to replace both batteries up front with the same size ones or can
I just buy a new engine battery? Like at least one other person, I haven't had a whole lot of luck following the
electrical diagrams in the manuals yet but I intend to study them more. I have a lot of time since I'm still
working and have not yet retired. The front battery tray was completely redone just before I bought the coach
last week so everything appears to be in very good shape.

Any help will be greatly appreciated such as a good brand and size.
Happy motoring

Date: Tue, 27 Jan 1998 16:36:29 -0800
From: Phil Swanson <>
Subject: GMC: Battery Locations

Hello fellow GMCers,

With all this message traffic about batteries and locations, I decided to check out my newly acquired 1973
Canyon Lands closer with respect to batteries and cables. I have the two golf cart 6 Volt types in series in the
front on the passenger side and one commercial battery back in the generator bay but I have no generator
however. The battery in the back is functioning strictly for reserve capacity. One of the horrors I have however
is the positive battery cable that runs underneath the coach on the left side to hook up the generator battery. As
I inspected the insulation on the cable, I saw places that are chaffing on the frame and taped, but thankfully not
worn through underneath. It would create one heck of a mess and/or fire if this cable decided to short out.
Suggest if condition of cable is unknown, that you inspect the insulation and replace the cable or disconnect
that back battery when not in use. I am going to invest in one of those little shut off switches at the battery post
so I can electrically disconnect it and if and when I ever need it, I can tighten the green knob and restore a
connection. I do not like the idea of this cable rubbing on sharp twists and bends in the frame. Maybe installing
one of those outer jackets for wire looms often seen on custom installations, like on hot rods, would help.
Anything to keep the cable from wearing through and creating a wild short. The bad thing about the stock
configuration that I have is that is always live and a short waiting to happen. Maybe I will just get rid of the
battery in the back since I have no generator. I could eventually get a Honda generator with rope start and get
rid of the battery and the added weight in the rear where the GMCs are too heavy anyway and eliminate the
possibility of catastrophic failure and possible loss of the coach.
Regards, Phil

Date: Mon, 26 Jan 1998 22:47:48 +0000
From: John Szalay <>
Subject: Re: GMC: RE: Battery locations

At 09:10 PM 1/26/98 +0000, you wrote:
>For whatever it's worth, I have a 78 Royale. Like you, I have two batteries on the right side of the engine
compartment. However, my house battery is on the left side of the engine compartment.

> Paul Bartz
>> I've got a 1977 Royale with three batteries. Two 12 V batteries (starting and House) in the front engine
compartment on a double battery tray and another 12 V battery in the Onan generator compartment for starting
the generator.
>> I also have read that putting dissimiliar batteries in the same charging circuit will/can result in one of the
batteries receiving insufficient charge.

That is true ONLY IF the batteries are connected in Parallel. If they are connected in series, its just as if they
were one large battery. after all, your 12volt battery is a series of small cells connected in series to give you 12

>>it would seem I can't/shouldn't use the existing charging circuit, which now charges the two front batteries
simultaneously, with a 12V battery on one terminal of the isolator and two 6v batteries on the other terminal.
 yes you can.

          +12-        +6-+6-

The biggest problem is where to mount the large 6 volt batteries.

I also have 3 batteries in my 73, one for the engine, one for the house 12V
and one in the back for the Onan genset.
> ----------
> > From: Robert Dinsmore <>
> > To:
> > Subject: Re: GMC: RE: Battery locations
> > Date: Wednesday, January 28, 1998 3:20 AM
> > John:
> > I removed the grill and welded a battery tray to the crossmember directly in front of the radiator/air
conditioning condenser. Then installed two Trojan 105 6 volt golf cart batteries in series rated at 200 amp
hours. Reinstalled the grill with stainless steel wing nuts and lock washers so I could easily remove the grill for
battery servicing.
> > Battery cables were kept short to minimize voltage drop and for the most part all wiring to the
inverter/charger is stock and left unchanged.
> > Then I replaced the original 12 volt starting battery and house battery (located on the passenger side) with
another two golf cart batteries that are used for only starting loads (1200 cold cranking amps that tell that 455
whose boss at 20 below zero in Wisconsin)

> > The 6 KW Onan has a small starting battery adjacent to it so there is no reason for heavy battery cables
strung the length of the motorhome.
> > The advantage of the 4 golf cart battery system is: #1, I can squander my battery power, and listen to the
radio any time I want without fear of discharging my starting battery... #2, In a pinch I can use the starting
batteries to operate the load in the house (400 amps hours available to run my VCR/TV and space heater
blowers in the winter). #3, As my house batteries die from hard deep cycling, I move the starting batteries into
the house battery tray and buy new starting batteries. #4, I have TRUE DEEP CYCLE batteries designed to
deliver 75 amps continously, not like most 8D truck batteries that are really just big starting batteries. #5, I
have lots of redundancy. #5, Since I live on a boat in the summers and use the motorhome in the winter I do a
lot of poor weather driving (22,000 miles in the last two years)... The extra weight up front comes in handy in
the snow(about 280 pounds for 4 batteries).
> > I notice no change in engine operating temperature, but I travel in the winter as far south as Arizona, Texas,
and Georgia. My plan was to duct air from the grill opening to the radiator if I encounter an overheating
problem, but so far I have not found it necessary.
> > I use a like setup on my sailboat, (except I have 800 amp hours), and I cruise 5 months of the year in Alaska
without electrical hookup during the entire time.
> > Hope this helps
> > Bob

Date: Wed, 28 Jan 1998 21:03:57 EST
From: (David L. Greenberg)
Subject: Re: GMC: Battery Locations

Watch out for those battery disconnects with the green knob. I installed one a couple of years ago and nothing
but problems with it. It either didn't shut down all the way (One of the wags at the Carlysle show told me it
allows a little voltage to creep thru to keep radio memorys working!) and sometimes it shut down when I would
try to restart after getting fuel, etc.

I threw it away and installed a Knife Switch. It is much more positive and you can tell at a glance whether your
batteries are in or out of the system.

Another approach is to use a rotary switch such as used on boats. In any event this works to have a theft
deterrent function as well.
David Lee Greenberg
GMC Motorhome Registry

Date: Wed, 28 Jan 1998 21:03:57 EST
From: (David L. Greenberg)
Subject: GMC: Re: Battery locations


Your battery arrangements sound ideal.

One comment to add...I have installed my grill with 4 springs. They go back to the radiator frame and I can
remove and replace the grill with out tools.

I like the idea of moving weight up front and I NEVER drive in snow!

David Lee Greenberg

Date: Fri, 30 Jan 1998 22:40:18 EST
Subject: Re: GMC: Re:GMC Re: Battery Locations

I'll add my two cents worth on auxillary battery position. I have a 77 Palm Beach. I did away with the battery in
back and put two 6 volt golf cart batteries up front on the curb side. They are positioned one in front of the other
with about an inch clearance at the closest point to the outside body. The engine battery is between them and the
radiator shell. I used the same cable from the old battery position in the back to carry current from the golf cart
batteries to the Onan. I have not had any problems. Since this is the vicinity the GM engineers chose for the
engine battery, I assumed it would be better than trying to find another location. It is also closer to the electrical
connections on the firewall.

As to additional weight and handling, I can't tell any difference. The batteries can be installed through the
eyebrow opening.
Justin Hill

Date: Fri, 30 Jan 1998 22:17:28 -0800
From: Robert Dinsmore <>
Subject: Re: GMC: Re:GMC Re: Battery Locations


I fill my golf cart batteries 1/2 way between the lowest part of the fill tube and the plates. These batteries
(Trojan 105) have a lot of water capacity above the plates. I have taken a 50 degree knock down with my
sailboat and have not spilled a drop of battery acid).

These batteries are "not" maintenance free... you need to check the water level at a regular interval.

If it still bothers you, you can purchase special marine type battery caps that are designed to recover water that
is boiled away during heavy recharge amps. Very expensive though.... so I ruled them out.

Philip L. Stewart wrote:
> I've read the discussions on installing auxillary batteries in the space behind the front grill and in front of the
A/C condenser, radiator and in my case an auxillary transmission cooler coil. What's anybody's guess about the
risk batteries in this location would pose to these parts due to the possibility of battery acid spills or corroisve
> venting from normal or accidental over-charging? I recently had to replace the radiator core on my coach and
sure would hate to have to do that expensive job again. If this is a safe location otherwise, it seems
> like a good place to mount additional house batteries.
> Phil

Date: Sun, 8 Feb 1998 09:56:33 -0800
From: "Mike Finnicum" <>
Subject: Re: GMC: RE: Battery locations

Hi All,

Lots of activity while I was at our monthly GMC rally. So here is my 2 cents worth.

Re: Weight up front vs. batteries.
I have my original style battery in the back compartment. At the club we have about 150 members with 50-60
regularly showing up at the rallies. I have surveyed the group and about 20% have moved batteries forward
(over 50% have switched to golf cart batteries). No one has yet moved them back. There are various reasons but
storage (using old bat compartment for elec cords, hoses, oil, etc.) and weight up front appear the biggest.

Alex Sirum who owns a large GMC repair center in Ochachobee, FL say the weight is negligible compared to
the total up front weight. He also says if you are wearing out bearings, check the hubs. If they are worn,
bearings will wear out 2 to 5 times faster. You should NOT be able to turn the bearing inside the hub. The front
axles are meant to carry 3500 lbs.. 75-100 lbs. of battery is only 2-3% of the total.

I am now planning to move mine up front at my next coach battery replacement.

Date: Tue, 17 Mar 1998 17:44:49 -0500
From: "John Massey" <>
Subject: GMC: Wiring for multiple batteries

Do I have a problem?

   I've got three batteries in my 1977 Royale - Starting, House and Generator. The Maintenance manual
diagrams, however, only show two. For example, the diagram entitled "1977 and 1978 GMC Motorhome
Living Area 12-Voly DC Electrical System...." show how the "cranking" battery and "Aux" battery are

connected. Part of my problem is that the House battery wire, that I would have expected to be routed back
from the front, where the battery is located, to the converter in the rear, is not. Tracing the wire under the MH,
the Red large gage wire is tied off in the vicinity of the generator and is terminated in a heavy ring terminal
which is not connected to anything! Two inches away there is a Red wire from the generator battery and that is
connected a stud terminal on what I believe to be a fuse (metal block about 2" by 3/4" with two studs). The
other stud terminal is connected to a Black very large gage wire which goes to the converter. The "fuse" is just
hanging in the air with the wires attached. So it looks like the way it is connected NOW, the generator battery is
only charged by the converter and the house battery is only charged by the alternator. Also the Generator
battery is the only source of 12 vdc for house needs.
     If I were to connect the Red house battery wire to the same stud terminal that the Red generator wire is
connected to, then, I think, I have the two batteries in parallel. Then both batteries would be charged by either
the alternator when the engine is running or, when stationary, by the convertor when it gets shore power or AC
from the generator. I am concerned that this would mean that, when the engine is running, the alternator would
be charging all three batteries - is this a problem?
   This would also mean that when I select BATT BOOST, all three batteries are available for starting.
   All three batteries are identical, looks as if they were bought at the same time about a year ago.
   I just don't see a reason for someone disconnecting the House battery wire in the first place and am a bit
apprehensive about reconnecting it. Hope this was clear enough.
FMCA 231235

Date: Wed, 18 Mar 1998 02:00:38 -0500
From: Bill Wallace <>
Subject: Re: GMC: Wiring for multiple batteries

John, I can help on this. My '78 Royale had same hookup. The "fuse" you describe is a circuit breaker to protect
in case of a short in the wire to the front coach battery. The breaker on mine was wrapped in tape. Breaker was
inoperative. Wire from gen and battery goes to one end of breaker. Wire from converter and wire from front
coach battery goes on other end. Size of breaker, about 40 amp should be stamped on it. I found one at Camping
World. I also replaced gen. battery with 2 golf cart batteries in series. Keep front coach battery to assist with
battery boost as circuit breaker at gen. will trip if starting with boost. It is automatic reset. This way you have
three batteries for coach operation. Iused replacement battery trays in gen. compartment to anchor batteries.
Engine gen. charges all batteries on road. Converter charges coach batteries when plugged in and genset charges
all coach batteries when running. Hope this helps.
If you need more let me know.
Bill Wallace

Date: Mon, 20 Apr 1998 09:24:14 -0700
From: "Heinz Wittenbecher" <>
Subject: Re: GMC: EFI project complete, looking for some 'tuning' info.

When I first got my rig (10+) years ago with a 70 amp ( I think ) installed I had a few alternator failures in a
relatively short time. In retrospect it might've been workmanship :-) of the alternators themselves. That was

before I knew anything about GMC's or the community. (I had always wanted one, the opportunity arose, and I
still have it :-)

On a trip to Buskirks early on (for sway bars, etc) it so happened that they had a used 150 and I bought it. We
changed the output wire to #4 (I think), i.e. large.

Whether I need it or would do it again? who knows :-) I've replaced/rebuilt it a few times but overall it's not
been giving any hassles other than being very picky about belt tension. Hopefully that's now solved as I have
the serpentine installed.

Load: originally I figured I'd be running the fridge on 12V while underway, but it broke and got replaced a long
time ago so now run on propane. I do 'cycle' my batteries lots. Computers (full size and laptop), cellphone(s),
used to have a satellite system for comunications before cell phones came around, etc.

With 20/20 hindsight the only reason for change would be psychological, I think. I.e. a 150 amp would work
less, last longer... equals less downtime (in one's mind :-)

With reference to the diode/battery splitter gadget (the proper name escapes me at the moment :-), after a couple
of failures I changed it to a relay connected 'ignition on' so that the relay is closed and feeds the rear house
battery when engine is running.

'76 Transmode

>You say you run a 150 alternator.
>What kind of a load do you have that requires that size alternator? Did you upgrade any of the original wiring
to carry the increased load? I've heard various people question the wisdom of not doing so.
> Paul Bartz
>> -----Original Message-----
>> From: Heinz Wittenbecher []
>> Sent: Friday, April 17, 1998 12:21 PM
>> To:
>> Subject: Re: GMC: EFI project complete, looking for some 'tuning' info.
>> Try going to this website
>> I run a 150amp alternator and it's always been more difficult to keep belt tension just right. >>

Date: Mon, 27 Apr 1998 14:16:12 -0600
From: Robert M Fukumoto <>

Subject: GMC: 12 volt power converter

I am a newbie working to get my 76 Palm Beach ready to take my first trip. I just got my monitor panel to
somewhat work and find that my 120v ac to 12 volt dc converter is putting out 18+ volts. I verified this with a

I can find little literature on this subject. The converter, from looking at the manual doesn't appear to be the
original. Books seem to indicate that converters should only put out between 14 and 15 volts.

Are there usually ways to adjust the output voltage on the converters? Am I risking damage to my battery with
such high output. Will this hurt my 12 volt appliances and radio? What should I look for in a replacement?
Can I install it myself or should I have someone like Camping World install it? Any help would be appreciated.

Bob Fukumoto
76 Palm Beach

Date: Wed, 29 Apr 1998 20:36:31 -0700
From: Bill Rush <>
Subject: Re: GMC: 12 volt power converter

I've done a bit of work on converters and you are right 18 volts is too high, however I'm no expert on the effect
other than overcharging the battery and having to watch the water level. What brand converter is it?

Bill Rush

Date: Sat, 2 May 1998 12:18:44 -0500
From: "Mark Grady" <>
Subject: GMC: Refrigerator question

Greetings all --

One of this year's projects is the replacement of the original refrigerator in our '77 Kingsley. It has 'sticky'
compressor valves that allow it to run without producing any head pressure and thereby cooling.

I've heard from a number of people who swear by LP units, but we seldom dry camp long enough to deplete our
battery string (a total of 4 6 volt golf cart units, two front and two rear.)

New RV style units are $1,000 and up, but I've seen some very nice looking GE 6.5 and 9.1 cu ft household
refrigerators that only consume an amp to 1.5 amps. We don't use the built in vacuum, and a little wood
working would easily make one of these units fit nicely.

There are now some very efficient modified sine-wave 12 to 110 volt inverters on the market. I even took a
portable power back and an inverter along and found that a 600 watt unit will easily handle the load (although I

didn't try it in a locked armature condition). It would seem easy enough to put the inverter in the closet and
power the refrigerator using 110 on that circuit through the existing wiring.

Anyone else out there have any thoughts or suggestions? Pitfalls I haven't considered?

This seems like such a simple solution. Have I missed something?

Thanks for your replies.

Mark Grady

Date: Thu, 21 May 1998 23:25:16 -0700
From: Jim Bounds <>
Subject: Re: GMC: Power modifications

Tim Jones wrote:
> There are other modifications I would make to the primary power circuit,
> give me and we can discuss them. 1-877-275-4462
> Jim Bounds
> Jim if you have some other ideas for the power circuits I would like to hear them. I am in the process of
installing a Todd converter/charger and would like to upgrade the electrical as I go. Does anyone know of a
small 110V circuit box that I could use to replace the household unit that is in my 78 Kingsley. Or better yet a
matched design for both the 12V dc fuses and the 110V ac circuit breakers. If I could find good design and
good function that would be a great package. Thanks to everyone for all of the information. It makes me
realize how much I have to learn.
> Tim Jones

I'm sure everyone is board of sifting through all the notes I wrote tonight, give me a call and we can discuss
specifics easier on the phone (1-877-275-4462). Basically, I would install a third battery with an A/B selector
switch and a knife switch to the chassis battery along with some wiring changes like the dash radio to the living
area battery, etc.

I've got a pretty neat AC/DC power panel that you could use if you're up for the wiring mods.

Jim Bounds

Date: Sat, 30 May 1998 18:53:54 EDT
From: (David L. Greenberg)

Subject: GMC: Battery Boost switch

Be careful. Early models didn't have a rocker switch for the battery boost and sometimes the switch is left in the
boost position or on. GM later changed this to a rocker switch. You only use this to put all batteries together to
help start your engine or Onan. Not to be used (and unnecessary) while the engine is running.

David Lee Greenberg
GMC Motorhome Registry
Delray Beach, FL

On Thu, 28 May 1998 00:36:37 -0400 (EDT) "Thomas G. Warner"
<> writes:
>Battery boost puts your living area battery in parallel with the
>engine battery and has nothing to do with the generator.


To the boost switch, it simply energizes the solenoid located above the battery up front which electrically ties
the rear and the front 12 volt electrical systems together momentarily. This will bypass the isolator which has
the job of splitting the 2 systems and allow the engine alternator to charge both while the engine is running.
This is desirable in that the chassis battery can be saved for starting the engine even after that wild night where
you left the coach lights on because the lamp shade on your head prevented you from seeing that you had left
them on after the belly dancers had left!

There are differences in the wiring logic of this circuit between the early and late coaches. I have found
modifications for both that their use. Give me a call toll free (1-877-275-4462) and we can go over the wiring

Jim Bounds

Date: Wed, 01 Jul 1998 06:02:19 -0400
From: Dick Kennedy <>
Subject: RE: GMC: Broken Alternator Belt


If your batteries are fully charged you shouldn't have any problem driving 5 miles without the alternator. I once
made it about that far at night with all of the lights on but that was with a running start and no other reasonable

My '75 palm Beach has the house batteries mounted behind the generator and the 40 amp DC supply for them is
powered when the generator is up and running. This is the vintage where the shore power cord must be

manually plugged in to the generator to make it work. The good news is that there is about a #2 battery cable
running from these batteries up to the front to a solenoid mounted on the firewall on the passenger side.

I believe this solenoid is connected to a battery booster switch on the dash. When the switch is active the front
and rear batteries will be connected together. I don't even know if mine actually works but the point is both
batteries have heavy cables coming to that solenoid. Jumper them together at the point and all of your house
capacity will be available to the engine system. Both batteries are also attached to the alternator splitter but I
believe the heaviest wires are at the solenoid.

Get yourself a good voltmeter and it is easy to check all of this out. On an earlier mini (actually later since it
was a '79) that I had I actually kept an alligator clip under the hood so I could couple the two batteries and play
the dash radio while on shore power. This was easier then changing wiring.
Hope this helps
Dick Kennedy

At 10:30 PM 6/30/98 -0400, you wrote:
>Well, I got the GMC running. Then the belt to the alternator broke. I want to move the coach to my house (
about five miles ). Can I use the onan generator to supply 12volts to the main battery to run the engine? Maybe
that's the way it works anyway??? If not I'll have to replace the belt where it sits. That can be done...But its in
the old REO building and really dirty place to work. It would be a lot easier to work on it at my house.
> Rob Teed

Date: Tue, 7 Jul 1998 22:29:24 EDT
From: <>
Subject: Re: GMC: Installing a home type fridge

Here is where I have some experience. My wife and I own a 56' houseboat with a 16 cf GE (residential type)
fridge. I don't like running the genset all night long when we are "coved out", the nautical equivalent of
boondocking. First there is the noise, second the danger of carbon monoxide poisoning (seen it first hand!) I
installed 8 golf cart batteries (880 reserve amps # 12v.) and a 2000 watt inverter. All this set-up does is gets me
through the night in peace and quiet. (When the morning comes, the genset comes on, the Jimmy Buffett cd's
get turned on, the inverter is now CHARGING at up to 100a, and the genset is running the fridge on AC.) All I
ask is about 10 hours of capacity, and I get it. These batteries only supply this inverter which is connected to
one AC circuit in the AC panel. House batteries and another dc charger handle the rest. You do need to bring
that much battery power back up to snuff, and this charging process really pulls some AC amps, let me tell you,
especially when the charging function is in the early stages. You need to get the air movement in the residential
box, cause tight fits hinder the cooling process. As for me and my Palm Beach, we are going to stick with
propane for the refrigerating process, but will use a scaled down golf cart battery / inverter setup for running the
tv. Have not gotten that far into the process.
Larry Nelson

Date: Thu, 9 Jul 1998 05:22:26 +0100

From: "Donald W. Miller" <>
Subject: Re: GMC: Installing a home type fridge


Not sure which you are asking about, but the boat has two Prevailer 8d's and the GMC has two golf cart house
batteries. If this sounds insufficient, the ULine is only 6 cu ft and has a tiny 1/6 hp 500 watt compressor. We
cram as much extra insulation around the box as we can fit in. Also add a layer of aluminum foil to reduce
radiant heating. On the boat, we can turn it off at bedtime and the ice is still frozen next morning. The Norcold
runs on 12v overnight but adding insulation around it has reduced its electrical consumption.

Date: Sun, 12 Jul 1998 18:22:32 +0100
From: "Donald W. Miller" <>
Subject: Re: GMC: GMC Alternator - need help


FWIW, some considerations.

1. Since most everything is built into your new alternator, it may have had a short life span.

2. Make sure #2 white wire has around 12 volts present with key on and when engine is running.

3. Your diode isolator might be bad.

If you understand how the diode isolator works, check it out with your ohm meter.

An alternate diode isolator check is to put a jumper wire between it's three terminals. If both engine and house
batteries charge properly with engine running and jumper in place, the isolator is the problem.

4. Look for corrosion at the terminals and connectors.

5. Check wire continuity from alternator output to diode isolator input.

6. Check two wires for continuity from isolator output to aux battery relay terminals.

Be careful, if the alternator does not have a load, when engine is running its output voltage can be high. High
enough to kill you and high enough to short out the alternator internal diodes.


>I was working on my 76 Palm Beach today trying to get it ready for its maiden voyage in two weeks. The
alternator stopped working. I removed the alternator and had it tested at the local Checker auto and found that

>it was fine. (I put in a new one though, the bearings seemed to be a little questionable). I tested the #2 lead
from the alternator to the battery junction block and it was fine. I haven't been able to find where the #1 lead
goes to. However, like the manual said, I tested all three leads from the alternator with the ignition key in the
on position. The #3 lead to the battery showed no voltage. The #1 lead to the dash light showed 2.4 volts. The
#2 lead to the battery junction showed 12.6 volts.
>As I read the manual, there is a shutoff of power production in the alternator if the #1 and #2 leads don't have
the proper voltage coming back into the alternator.
>I can use all the help and ideas that anyone can give me on what's causing the alternator not to put out any
voltage. >
>Bob Fukumoto

Date: Tue, 14 Jul 1998 22:59:57 EDT
From: <>
Subject: Re: GMC: Installing a home type fridge

I've got to jump in again on the "home fridge" debate. If one is on the road a lot, an engine driven compressor
and holding plates in a well insulated box is right out of the ancient mariners handbook. Seriously, our rv boxes
are very poor, and they open the wrong way ----in front. We lose lots of coolness all over our tootsies, every
time we open the door. Then the machinery has to go back to work. Well made marine boxes are top loading
and have a min. of 4" of insulation, hopefully 6". Many mariners have tried kerosene fridges, but they must be
gimballed to keep them level as possible. For my money, the 3 ways are not a bad solution. The propane is safe
if installed properly, it's available, and it's noiseless. I will stick with my huge bank of golf cart batteries in my
houseboat (+ 2000 watt inverter + 17 cf fridge), but in the Palm Beach its propane and line voltage for me.
Larry Nelson Palm Beach 75

My converter was throwing off 18 volts and there was no adjustment to change the voltage. The company that
made the unit was out of business so I ended up buying a Magnatex converter which, by the way, I have now
heard good and bad things about.

I replaced the isolator early on because I was having trouble with the original batteries charging. As it turns out,
the batteries were bad and the isolator was ok but I kept the isolator.

I was told by several GMC Western Staters that the heater hose shutoff valves never quite shut off the flow and
in hot weather you can feel the heat coming out of the vent system. Since it was cheap I just put in a ball valve
(around $6) with two 5/8" hose barbs in the place of the original shutoff valve which was between the two front
access doors on my coach. I also have an added on heater under the front dining room seat that was hot to the
touch after driving only a short distance so I put a shutoff on that too. Of interest in my coach is there is a
device under the coach, to the front of the door that looks like an old style home steam radiator made of copper
pipe. It is hooked up to the heater line that flows to the bath water heater. I can only assume that it is there to
dissipate heat and it seems like a decent idea to me.=20

My water temp gauge runs between 190 and 200 when I have had it out on hot days. Does this seem normal to
all? By the way, I just put Castrol Syntec synthetic oil in both my engine and Onan and Prolong Oil treatment
in the engine and Prolong transmission treatment in the AT. I was pretty convinced (or gullible) by the
infomercials on TV. We'll see how it works.

Bob Fukumoto
76 Palm Beach newbie =20

Date: Tue, 04 Aug 1998 08:40:18 -0400
From: Dick Kennedy <>
Subject: Re: GMC: Converter recommendations?


Those old power supplies use what is called ferroresonant technology. I've had to repair mine twice in the past
year. Most recently when the starter bracket broke off the generator while the generator was running it burned
the terminals off the coach battery and also blew the convertor. I don't know if it was the short itself or the
transient that caused the problem. Inside the convertor there's a huge transformer, a rectifier, and some big AC
capacitors. These capacitors resonate with the transformer winding and are the basis for the voltage regulation.
Mine is a Triad unit and it had a pair of 4 of 650vac caps connected in parallel inside. Last fall one of these
caps was shorted and last week I replaced the other one. I had difficulty locating the 4u caps and when I finally
did they were very expensive so I replaced each of them with a pair of 7.5 u # 370 vac caps in series. It now
works just fine and is now back inside humming away. So yours is probably repairable if you can find someone
to do it at a reasonable price.

The problem with these old beasts besides the amount of iron in them is that they draw a lot of standby power.
If my memory is correct mine drew about 70 or 80 watts standby with no load. This is enough to make the
transformer run hot and is more power than I want to leave plugged in full time when the unit is parked at
home. I then retrieved a similar unit from an RV that I had sold to a friend. It's stand by power was pretty much
the same. My GMC is a '75 and the other RV was a '79 and the two supplies were very similar but not exactly

As the next step in this saga I obtained a more modern supply from an rv surplus place. The modern units are
wired differently. On the GMC the coach battery is on line all the time and the supply keeps it charged. On the
newer stuff when on AC the battery is switched off line and is trickle charged while raw rectified AC is fed to
the coach itself. The problem with this system is that many solid state items won't work from unfiltered DC. I
assume that newer RV's must route both raw power for lights and battery for the critical things. This is probably
technically a better system since there would be less cycling of the batteries. I didn't want to get into making
changes so I returned that supply to the dealer.

In this same time frame I was getting back into ham radio after being out for 30 years. I purchased an Astron
RS-35 ( supply for use with the ham gear. This supply is regulated and filtered at
13.8v. It would be a candidate for a replacement unit but since it's not designed for use as a battery charger I
would assume that it would drain the battery when unplugged. Astron also sells a line of switching supplies that

are much smaller and presumably more efficient. Last fall I sent an email to Astron asking some specifics for
our application but they never responded.

This is as far as I took my search. I solved the standby problem by leaving it unplugged when I'm at home.
These newer designs are smaller and more efficient than the old ferroresonant guys but I didn't really find
anything that fit exactly what I needed so I stayed with the original. It would also be nice to have a quick charge
mode built in.

These Astron supplies are available used for under a $100 so if my supply failed today I would probably put the
Astron in the RV and use a high blower relay for isolation if necessary. From the postings there are other
alternatives also but I don't know the relative costs.

Hope these ramblings help someone.


At 02:55 PM 8/3/98 -0400, you wrote:
>Noticed that my converter -- looks to be original -- doesn't always want to work even though it hums up a
storm. Any recommendations about which models I should check out? What are some of the differences that
more experienced folks have found and what sources do you recommend?
>Thanks for the advice.
>Ralph Edelbach, '74 Glacier (still being gone through!)

Date: Tue, 4 Aug 1998 18:07:52 +0100
From: "Donald W. Miller" <>
Subject: Re: GMC: Converter recommendations?

Another problem with these old ferroresonant chargers is they keep charging your batteries until they are
cooked as they don't cut back enough.

I would suggest checking marine stores before spending hard earned dollars to buy outdated ferroresonant

The boating industry threw them overboard awhile back and went to greatly improved chargers which have a
three modes of charging. They quickly charge your battery until about 90% charged, then switch to a
conventional charger until 100 percent charged, then enter a float mode to supply no more than is needed to
keep them charged. This greatly extends battery life.

Some of the larger 120v inverters include this type of microprocessor controlled charger when on shore power.
One of them has a nice feature that monitors total shore power current and automatically reduces the battery
charging current to keep from overloading shore power circuits while you use other appliances.


Date: Wed, 5 Aug 1998 02:29:17 EDT
From: <>
Subject: Re: GMC: Converter recommendations?
  Had the same problem with my '75. My converter used 3 big capacitors (~ 4 ufd) in parallel, rated for 660V.
The first year I owned it ('96), one of them shorted out (diagnosis was easy once I got it apart, the end cap of the
bad capacitor was bulged out!) With some long-distance advice from a friend who services battery chargers, I
merely cut the bad cap out of the circuit, which got things going again for a while.
  (Incidentally, my friend told me that these ferroresonant power supplies are considered quite durable and safe.
Says you can short the output leads together without damage if you're brave. Since I'm poor, this reinforced my
inclination to stick with the original converter. Finding that the so-called high-tech converters switch the
batteries out of circuit when charging, feeding barely filtered DC to the coach, cinched the decision.)
  The quick-and -dirty fix got me through summer '96, but the next year another capacitor blew. Went
shopping at the local electronics surplus/used shop. Couldn't find exact replacements, but found 3 4 ufd caps
rated about 400V that would fit the mounting brackets. About $3 each brand new, IIRC!
Took 'em home, bolted and soldered 'em in, and all is well. Still working fine 1 year and ~6,000 miles later.

Good luck.
Rick Staples

Date: Sun, 9 Aug 1998 12:27:07 -0400
From: "Tom Winslow" <>
Subject: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893

I am trying to determine what is causing the generator battery to drain. From a full charge the battery list charge
in 24 hours with everything off except the gas refrigerator and freezer. Can anyone offer a suggestion or a test

Tom Winslow

Date: Sun, 9 Aug 1998 14:03:57 -0400
From: "Samuel Pickens" <>
Subject: Re: GMC: Generator Battery Draining Down

Tom, only one thought. Someone prior may have spurred in from the main batteries without going through the
switching. All I got. Regards, Sam Pickens

Date: Sun, 9 Aug 1998 19:50:36 EDT
From: <>
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893

     I drained my Engine (Generator) battery at the Indy 500 when the 12 volt TV set was left connected to the
Cigarette lighter outlet over that weekend. I found out later that the TV should never be left connected to this
"direct current" when it is not in use. Also, It took a Service Truck to get the Coach started.

I now have a "direct current" 12 Volt outlet installed for my TV - it is wired directly to the "House Battery".
Regardless to where you get the electric power, you should not leave the TV plugged in when the coach is in
"Dry Dock.

Hope this helps,
Don Martin

Date: Sun, 09 Aug 1998 23:16:32 -0400
From: Dick Kennedy <>
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893


On the door of the fridge in my '75 Palm Beach there is a switch marked with something about humidity. It's
apparently some sort of frost free feature. If it's left on it will drain batteries in a day or so and there is no
indication other than the switch position. I believe it even draws power when the fridge is shut off. It zapped my
batteries once last year and again this year but I still haven't gotten around to disabling it. Yours could have this
gremlin also.

All of the current from the house battery should be passing thru the fuse block. If you're drawing enough
current to drain the batteries in a short time you can probably detect a small spark when you make & break the
circuit. That's how I found the fridge current this last time. One of those light bulb continuity testers is the next
logical step for trouble shooting. I usually never know where mine is but I do always have a DVM handy.

You can either use a DVM to measure current directly or deduce current by measuring voltage drops. When
DVM's are in current mode they are actually measuring voltage across a calibrated meter shunt. It's possible to
use a length of wire or measure across an existing wire to create your own meter shunt. I don't remember the
precise details but the '79 GMC chassis that I had had about a number 10 wire from the alternator to the battery.
I used a sharp point to pierce the insulation and spread the wire strands in two spots about a foot apart (I used
some wire tables and some experimenting to find just the right distance). Then when I inserted the DVM probes
in the holes I had an ammeter that was calibrated 200 amps full scale, had 100 ma steps, and didn't blow meter

You probably don't need to get as fancy as making calibrated shunts but as a practical matter it's usually
possible to find points on the wiring harness where voltage drops can be measured to deduce where the current
is going without actually opening any circuits to measure it. Your situation seens to have enough drain that
there should be enough drop across the fuse block to deduce which circuit is the problem. The offending circuit
will have a few millivolts drop across that fuse.

Hope this helps


Date: Mon, 10 Aug 1998 02:21:38 -0700
From: Jim Bounds <>
Subject: Re: GMC: GMC Hams

You are right, a good converter will save you many $ in dead batteries, I also have a few primary wiring mods I
do to units that logically help conserve current and that's what 12 volt circuits need to do! I also employ a 30
amp solid state converter that I have had very good luck with. They run about 175.00. For a little more, they
also have a 40 amp. model that works well too!

If you would like to talk further about the 12 volt mods I do, give me a call toll free on Friday at 1-877-275-

Jim Bounds wrote:
> I would suggest that you cannot spend too much money on a charger for your valuable batteries. Smart
chargers, with three stages of charge, are the only way to go, or, trust me, you'll be replacing your batteries
every year. A good 30 amp charger will cost over $300 discounted, but will be the way I go after all the
mechanical systems are to my liking. BTW, the SGC is an almost "industrial" ham rig, also used by the
military. I have all the back issues of GMCMM and particularly look at the ham radio installations on the
Coach of the month.
> I have been collecting battery/inverter data for years + I operate a tour boat that is a battery test bed. I'll be
adding a 50w solar collecter to the roof of my coach along with a systems monitor. Already have a Heart
Inverter (700w) from my last coach. Larry Nelson, Palm Beach 75

Date: Mon, 10 Aug 1998 11:48:42 -0600
From: Robert Shimanek <>
Subject: Re: GMC: Generator Battery Draining Down

At 02:03 PM 8/9/98 -0400, you wrote:
Tom: Another thought: How old is your battery? Maybe your battery is only accepting a top charge. Will all
your electrical components off you can install an ampmeter which is incorporated in most volt/omhmeters.
Install it in series with your battery positive lead and if you note an amp draw start removing fuses until it reads
zero. That will be the culprit that is causing your drainage.


Date: Mon, 10 Aug 1998 21:54:59 -0500

From: "Mark Grady" <>
Subject: GMC: Battery Draining Down / Finding current draw (derived thread)

> -----Original Message-----
> From:On Behalf Of Dick Kennedy
> Sent: Sunday, August 09, 1998 10:17 PM

>When DVM's are in current mode they are actually measuring voltage across a calibrated meter shunt. It's
possible to use a length of wire or measure across an existing wire to create your own meter shunt.

Mark Grady writes:

At work, I chase DC current loops and the mischief they create for a living.

I have an English made Simpson clamp around DC 'amprobe' style meter. It cost the company about $3,000 and
it's worth every penny.

At home, I have a Japanese made Extech Instruments AC/DC clamp meter that I got from:

   Bob Cain - The Meter Man
   PO Box 1280
   Bethany, OK 73008

   v: 405-722-0339

It is just as accurate as the Simpson. It does AC, DC, temperature, voltage and resistance. It cost less than $200,
and it too is worth every penny.

If you want to find out where you're 'leaking' 12 volt power (and how much) this is the ultimate tool for the job.

A 12 volt test light in series with the suspected circuit (as well described in Dick Kennedy's message) works
great, but if you have problems you can't resolve, get your hands on a clamp style DC meter and you'll make
quick work of solving any DC related problem.


Date: Tue, 11 Aug 1998 02:29:59 EDT
From: <>
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893

  Standard test procedure for checking for current draw ("parasitic loads" to get fancy) is to use a common test
light. (Multimeters tend to be too sensitive on the volts scale, not sensitive enough on the amps scale, and will
usually self-destruct if you make the mistake of using the ohms (resistance) scale on a live circuit.)

  Shut everything off (including your refrigerator), disconnect either battery cable, and insert the test light
between the cable and the battery (ie: in series with the battery). It should not light (a dim glow is acceptable if
you have "memory" devices connected). If the test light lights, you have something drawing current from the
battery. Isolate it by removing one fuse at a time until the test light goes out. The last fuse supplies the
offending circuit.
  If everything checks out, use an ammeter (amps scale on your multimeter if it has one that goes up to 3 -4
amps or more) to check the current drawn by your refrigerator. Compare with your refrigerator specs to see if it
is excessive.
  Finally, your battery(s) may be dying. Have it charged and load tested to find out.
Good luck.
Rick Staples

Sent: Tuesday, August 11, 1998 7:32 PM
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola

I had a similar problem and found the battery isolator was the problem.

Russ Bethel

Date: Tue, 11 Aug 1998 23:14:34 EDT
From: <>
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893

Here are some things to check for.

1. Make sure the amp on your TV antenna is turned off.

2. Make sure any 12v televisions and or VCRs are unplugged. They still draw voltage when off.

These problems assume that the gen battery is also the house bat.

Next --mine is behind the closet module--check the fiber block where the positive cable is bolted to sidewall.
Mine was oil soaked and causing a small drain.

If the house battery and gen bat are the same start pulling fuses until the drain goes away. If they are seperate
batterys try cleaning everything between the gen and battery. Pay special attention to the selenoid. A track down
the side can cause a problem. Take it out of the circuit and see if the drain is still there. Good Luck.

Take Care

Date: Tue, 11 Aug 1998 20:51:26 -0700
From: Bill Rush <>
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893 wrote:

I had a bad stator on my generator a while ago. You can isolate the stator and check to see if you still have
draw on your battery.

Disconnect the generator battery. There are two wires from the stator (located under the flywheel) one goes to
the voltage regulator terminal marked "AC" and the other goes to the printed circuit board terminal 2.
Disconnect both of theses leads and reconnect the battery. If you still a draw on the battery keep looking. If
there is no draw look for about $200 to replace the stator. Don't try to start the generator with these leads
disconnected. Bad things happen.
Good luck

Bill Rush
26 Canyonlands

------------------------------ From: <>
Subject: Re: GMC: Generator Battery Draining Down - 1977 GMC Coca-Cola TZE167V101893

TW wrote:
> What is the battery isolator?

  It's the finned aluminum thingie mounted high up on the aluminum electrical plate way up front, passenger's
side. Basically 2 hefty diodes on a heat sink, it takes the output from the alternator, and allows rhe current to
flow into both the chassis and house (or generator) batteries, without allowing current to flow back fom one
battery to the other. Idea is if you run down your house battery(s) watching TV etc, you still have power in the
chassis battery to start the engine in the morning.
  If yours is bad (doesn't perform as described above), bigger more rugged ones are available from J.C.Whitney.
Good luck.

Rick Staples

Date: Sun, 16 Aug 1998 09:30:45 -0700
From: "Heinz Wittenbecher" <>
Subject: RE: GMC: Alternator question and comment re 4bagger and disc brakes... add

> I took a look at the GM book since you probably don't have yours with you. Oddly enough it says little about
voltage but mentions above 15.5 as too high with a fully charged battery. They say get out the hydrometer and
> don't forget to water the batteries.

> They mention checking the #2 lead with an ohm meter to make certain it is not grounded. The insulators are
sometimes left off or brush leads become shorted to ground, etc. This lead is connected to the battery through
the fusible link and would blow it if there was a ground fault.
> Another item is the higher than normal heat. As temps increase the voltage needed to fully charge the battery
decreases. The regulator has a thermistor to compensate for temp and it may be defective.
> Prevailer gel cell optimum varies from 14.5 volts at 32 F to 13.2 volts at 122 F. Flooded cells are a few tenths
volt different but I forget whether it is less or greater.

Thanks for the confirmation re lower voltage when hot. I thought that was the direction but it could also have
been a case of mushy brain/heatstroke.
Glad it's not gone altogether (the brain).
> I don't think you can put the field plug in backward but if so ????????

I don't think you can either but it's worth a double check. thanks.

> Then there is the infamous diode isolator which may be a contributor. It will have some voltage drop across it
so the alternator voltage will be higher by the amount of that voltage drop, than a system without one.

The diode isolator went out many years ago on the recommendation of an RV expert and as that was before I
knew better, a solenoid has been in There many moons. In retrospect, I actually think that may have been the
cause of what I Call many alternator failures over the years (instead of my abuse of electrical power). As I had 2
Alternators fail in as many trips I was in a better to position to retrace circumstances (I.e. I could still
remember). On both trips I used Roof Air, i.e. GenSet running and providing some 12vdc as
Well as Alternator running providing some 12v. When solenoid is engaged it's a direct connect between
batteries and charging source(s). I have to ponder and ask another question to the electrical experts. but in the
meantime I'm keeping them isolated when both are running.

> Many cruising boaters have replaced diode isolators with a solenoid actuated by the engine oil pressure
switch. Said to be much more reliable.

I have the solenoid on ignition so that with key off the batteries are isolated and I can drain the house battery
without affecting the front and as a solenoid usually fails open it further protects the front batteries
from un-authorized drain.
> In any event the voltage sounds too high to me.

Date: Wed, 23 Sep 1998 09:28:41 -0600
From: "Richard Guthart" <>
Subject: Re: GMC: convertor, fan clutch

I noticed the Caspro catalogue lists a 60 Amp (actually 2x30 amps) convertor/charger. Does anyone know how
the Caspro and Todd units compare? What are the differences between them and, especially, which is better at
rapidly but gently charging the coach batteries and tapering the charge so as to not fry them?

Dick Guthart
'77 Birchaven

>I've been told the best replacement for my dead convertor is the 75 amp unit from Todd engineering. Where
can I get one at a good price? Also, I've been told I have the wrong fan clutch, and need the heavy duty clutch.
Which one of those in the Parts Interchange Index is that? It lists a NAPA 271303 (I have the 455) and a "no
roar" Hayden 15-4298. The one I have now doesn't roar, is it the one that roars that's the heavy duty clutch? By
"roar" I assume they mean the roaring like that which accompanies a fan with a frozen clutch.
>Everyone has been great about giving me help. I appreciate any info on this you can offer.
>Darryl Kiehl

Date: Wed, 23 Sep 1998 08:54:07 -0700
From: "Heinz Wittenbecher" <>
Subject: Re: GMC: convertor, fan clutch

I've been using the Caspro chargers for many years. I have them mounted inside behind the gen/bat
compartment (but inside under my bed). Not a favorable place for cooling, but they seems to survive.

It has a gentle charge and rapid charge setting, controlled by adding a toggle switch. I use it mostly in gentle
and have only used max when charging with genset and wanted shortest charge time. (Max only recommended
for a 24hr stretch at a time).

I'm always plugged in at home, i.e charger is on line at all times.

It makes very little noise (if any), i.e. have to really listen for it with your ear pressed to the mattress (and it's
not just the mattress absorbing).

I ran a 110 circuit to the charger(s) and connected straight to the battery with a 50amp/12V (I think) circiut

No fans to distribute dust.
My 2cents

Date: Sun, 27 Sep 1998 22:54:59 -0500
From: "Stephen J. Galovic III" <>
Subject: Re: GMC: Battery Charger

Not to sound too simple, however, one of the first things we did to our coach was to relocate the radio and the
interior cab lights to the house wiring (battery) to avoid the problem you are currently experiencing. In the early
year models the battery boost switch on the dash could be left in the boost position, later years had a spring
return on this switch to the normal position. If put in the boost position when connected to shore power all
batteries will be receiving charge, when dry camping all batteries are being discharged (beware). In the normal
position the motor battery is isolated from the converter charging and house draining. We installed a fuse block
behind the glove box, sourced from the hose wiring, and fed through fuses to the radio, cockpit reading lights,
and anything else we might put in later such as ventilation fans etc.

Date: Sun, 27 Sep 1998 22:07:13 -0700
From: "Don W" <>
Subject: Re: GMC: Battery Charger

I too did the same modification on my '77 Palm Beach. I also hooked the cigarette lighter into the house battery
so my cell phone would not drain the engine battery. This stopped my problem of a dead engine battery after a
weekend outing.

Date: Mon, 28 Sep 1998 07:43:56 EDT
Subject: Re: GMC: Battery Charger

I had same problem, I ran a #10 wire directly from my radio to the terminal on the coach battery. Now I play
the radio all the time and never worry that I won't be able to start the coach.

Date: Mon, 28 Sep 1998 10:30:30, -0500
Subject: Re: GMC: Battery Charger

Yup me too.

I put the TV, CB, Radio, CD player -- all on a switch so I can select coach (ACC) or Coach battery. Mounted
the switch in the driver's side pouch. See article

Date: Mon, 28 Sep 1998 11:14:05, -0500
Subject: Re: GMC: Battery Charger

oops forgot to say

A lot of folks keep a clip-lead near their isolator and jumper across the two bat terminals so that the shore power
charger will charge engine bat while stopped. Problem is to remember to take it off. Not very satisfying , not
a good idea to charge bats in parallel, but good idea if your bat is dead and need to charge from the generator or
shore power.

Date: Mon, 28 Sep 1998 22:25:15 -0700
From: "mr.c" <>
Subject: Re: GMC: Battery Charger

Isn't it easier to jump the solenoid rather than using the jumper to jump the isolator. I just jump the solenoid,
and charge both batteries.

Al Chernoff wrote:

> Philip.........When you're parked, a heavy jumper wire between both heavy lugs on the battery solenoid will
solve that problem. Be sure and remove it when you get ready to drive away. I keep mine clipped on the wire
next to the solenoid so it's readily available. I also keep a tag on the steering wheel to remind me to remove it
before leaving. Senility, you know.........Jim Davis
 Phillip..........I found my jumper wire method once caused an isolator failure....My solution: Mounted a one and
a half amp battery charger below the isolator, on the firewall. Cost about $30 at Walmart...Ran the 110 Volt
wire back to the plugin under table behimd the passenger seat...The little charger is about four inches by 3
inches by one inch...Works well for me, I run both the radio and the front TV off the vehicle battery. I need all
the juice I can conserve for the house battery to run the old fridge and furnace.....This little charger, if anyone
interested, is called a Mity Mite I think.

  77 Eleg II Gil in Iowa

Date: Wed, 30 Sep 1998 07:46:09 -0400
From: Patrick Flowers <>
Subject: Re: GMC: Jumpering solenoid

Ritch Hwang wrote:
> I'm confused by all these references to jumpering either the isolator or boost solenoid to charge the starting
battery using the converter or genset. Wouldn't setting the solenoid to boost do the same thing? That is, tie the
house/generator batteries to the starting battery?

The "boost" switch is spring loaded in later models and will only stay there as long as you hold it.

Date: Wed, 30 Sep 1998 10:56:55 EDT
Subject: Re: GMC: Jumpering solenoid

  On my '75 (and I believe all newer units) the boost switch is a momentary type, so you'd have to hold it down
continuously to charge the batteries.
  Even on older coaches I don't recommend leaving it in "boost". The boost solenoid(s) (there are 2 on my
coach, the rear one bypassing the circuit breaker when "boosting") draw at least an amp or two each through
their windings when energized, so you'd be wasting current. Also, they are essentially starter solenoids, and so
are not really designed for continuous use. Just my .02.
Rick Staples

Date: Sun, 11 Oct 1998 15:47:59 EDT
Subject: GMC: Converter Problem?
When we heard the heater come on early in the morning, then listened to it getting slower and slower and
awakening to no lights, we realized we were running off the house battery and no 110 being converted to the
battery for charging. We thought it unusual that the meter for the house battery was showing low. Let me
backup by saying we may have fritzed the water heater and hat switch is in the same outlet the converter is
plugged into. Upon parking and getting things ready for a short weekend we realized we had not turned off the
hot water heater switch from before. We do not drain the tank but open both valves in back to empty fresh
water tank and pump, therefore we don't know how much water if any is left in the hot water tank. We plugged
the GMC in to 110 the evening before to get the fridge cold. The tank should have been hot unless we burned
up the element, should the tank empty past half then that is most certainly what happened. The question is why
did that affect the converter, if it did? Or are these two separate events?

Date: Tue, 13 Oct 1998 16:18:40 -0700
From: "Tipton, Eric" <>
Subject: GMC: House batteries

It is time once again to replace my house batteries. Last time I replaced to original equipment D4 size with a
bank of 3 size 24's. I am contemplating two large 6 volt Trojans run in series. Is anyone running a similar
configuration. Any and all input is appreciated.
Eric Tipton

Date: Tue, 13 Oct 1998 20:52:40 EDT
Subject: Re: GMC: House batteries

I am about to do the same. I too want to go to 2 big 6 volts for house bats. I also would like to hear about 2 big
6 volts for starting bats. With 4 big 6 volt bats on board I think I would have some real STAYING power.

Take Care

Date: Tue, 13 Oct 1998 21:09:31 -0400
From: Jack Ford <>
Subject: Re: GMC: House batteries

I have two six volt golf batteries I run in series, And it serves my coach very well.
Jack Ford

Date: Tue, 13 Oct 1998 21:33:18 EDT
Subject: Re: GMC: House batteries
How many amp hours? Do you boondock much? What kind of charger? Sorry for so many questions.
Take Care

Date: Tue, 13 Oct 1998 23:18:32, -0500
Subject: Re: GMC: House batteries

The recommendation is for two 6 volt golf cart batts for the coach, however it is recommended to use a large 12
volt for the starting batt. Now I will have to go find my notes to see why the 12 volt. It was something like the
12 volt has better starting characteristics and the golf cart batts have better long term drain characteristics. I will
get back.

Date: Wed, 14 Oct 1998 09:12:32 -0600
From: Gerald Schmitt <>
Subject: Re: GMC: House batteries

For house batteries use two six volt golf cart batteries in series. If you use two twelve volts in parallel, they will
try to charge each other and result in fewer available coulombs than if you go the six volt route.

Golf car batteries are an excellent choice as they are designed to be drawn down rather far then recharged.
Starting batteries are designed for lower internal resistance so they can provide high power density for short
periods of time.

On my coach I put an auxiliary battery holder on the driver's side and have the starting battery there and have
plenty of room for a pair of golf cart batteries on the other side.

Hope this helps, Jerry


I run 2 golf car batteries (Trojan 104s) in the rear battery compartment of our Palm Beach. The larger capacity
batteries are too tall to fit into the compartment without some modifications. I've gone to the
TrueCharge 40+ battery charger available from West Marine under their brand, or from Statpower (the
manufacturer) in British Columbia.

Using this setup I can go 2 days during the summer before I need to recharge. During the 2 days, our load is
primarily determined by the fridge. We still have the original fridge, so I don't have the option of propane. We
used 2 lights (originals) for 2-3 hours per day, ran the radio a bit (1-2 hours per day) and still had enough juice
left in the batteries to start the genset. Once I had to start the coach first in order to start the genset - after we'de
run 3 days without any recharge.

Things to do that will extend boondocking time:

1. get a propane fridge! Probably the biggest improvement.
2. when boondocking use the "middle 50%" of the battey bank capacity. This means discharging until about
30% capacity is left and then recharging to 80% using the genset. You can rechage the 50% in about
2 hours depending on the charger. Shore powered recharge to 100%.
3. consider halogen lights or florescents (best) for better efficiency
4. look at your DC systems that include dimmers or speed controls. If they use load resistors for controling
speed consider replacing with an electronic PWM controller, it's more energy efficient but more
5. switch to a charger like the TrueCharge that can recharge to an 80% level in a few hours ( I try to use only
about the middle 50% of the battery bank capacity since it recharges quickest)

You can also get a good feel for your own power consumption by installing an ammeter on the house battery
and watching your load. Alternatively, run a few specific tests like I did to determine how long your battery
banks last under what you think will be your typical usage. Lastly, make certain that your house and coach
batteries are isolated - that way when you make a mistake, you can still get everything started. Or, if you're
really paranoid like me, carry a portapak booster battery just to make sure.

Henry Davis

Date: Wed, 14 Oct 1998 12:22:24, -0500
Subject: Re: GMC: House batteries

See I knew someone knew the answer. There was a thread several months ago that recomended the best golf
cart batt. I remeber one suggestion was to go to the local company that repaired golf carts and ask them
what is the best battery.

Date: Wednesday, 14-Oct-98 11:18 AM
From: Gerald Schmidt
Subject: Re: GMC: House batteries

For house batteries use two six volt golf cart batteries in series. If you use two twelve volts in parallel they will
try to charge each other and result in fewer available coulombs than if you go the six volt route.

Golf car batteries are an excellent choice as they are designed to be drawn down rather far then recharged.
Starting batteries are designed for lower internal resistance so they can provide high power density for short
periods of time.

On my coach I put an auxiliary battery holder on the driver's side and have the starting battery there and have
plenty of room for a pair of golf cart batteries on the other side.

Hope this helps, Jerry

Date: Wed, 14 Oct 1998 09:38:14 -0700
From: "Tipton, Eric" <>
Subject: RE: GMC: House batteries
Jack - what is the size of the batteries, cost & brand?
Eric Tipton

Date: Wed, 14 Oct 1998 22:04:33 EDT
Subject: Re: GMC: House batteries

Could you tell me about the auxiliary battery holder on the drivers side? Where did you get it and where did you
put it? I have this problem of my 76 Glenbrook being a real half breed. It has the large air tank mounted on the
drivers side. Yet it has a second design hot water heater. Yes, mine has the old Power Level system. I have
second design windows-----with fixed windows in door and galley. I never know where things should be.
If you have a pic of your set up it would be great otherwise-----talk to me.

Take Care


Date: Thu, 15 Oct 1998 09:05:35 -0600
From: Gerald Schmitt <>
Subject: Re: GMC: House batteries
Hi Arch,
My air tank is on the passenger side so there was plenty of space behind the steering column. The holder was
one I had from JC Whitney is was sized to fit the largest conventional battery. I made the brackets.

Date: Thu, 15 Oct 1998 14:18:55, -0500
Subject: Re: GMC: House batteries
 Expanded recipient data:
 To: Gcbr                    \ America On-Line: (gcbr)
Ragusa has cast Aluminum battery pans both single and dual for the GMC.
Addr is on the site.
gene --

Date: Sat, 17 Oct 1998 01:02:05 +0100
From: "Donald W. Miller" <>
Subject: Re: GMC: House batteries
I removed the bat back of the genset because too much weight, too far aft of the rear axle is detrimental to good
handling in most vehicles. More weight back there and the tail starts to do more of the steering. I appreciate
superior road manners so I'm trying to lighten my GMC's tail. OK, while on the subject, adding up the heavy
items behind the rear axle. Propane tank, water tank, spare tire, aft air conditioner, 8d battery, Onan and trailer
hitch were on mine. Did I miss anything? All are heavy items and enough weight to probably be detrimental to
good handling. Too much weight and the tail starts to do more of the steering...... sounds familiar does'nt it ?
Onan cranks fine with full batteries up front but hav'nt tried it yet with low batteries. Don't really care as I plan
to be rid of it too, if the big 12v alternator and inverter system prove to be adequate.
Don Miller
>Thanks for the info. This seems to be a different approach than I have heard of.
>Do you still have a bat back next to the gen set?
>Take Care

Date: Fri, 16 Oct 1998 17:10:35 -0700
From: "Tipton, Eric" <>
Subject: RE: GMC: House batteries
How large an alternator & inverter are you running?

Eric Tipton

               -----Original Message-----
               From: Donald W. Miller []
               Sent: Friday, October 16, 1998 5:02 PM
               Subject:       Re: GMC: House batteries

                  I removed the bat back of the genset because too much weight, too far aft o the rear axle is
detrimental to good handling in most vehicles.
                  More weight back there and the tail starts to do more of the steering. I appreciate superior road
manners so I'm trying to lighten my GMC's tail.
                  OK, while on the subject, adding up the heavy items behind the rear axle.
                  Propane tank, water tank, spare tire, aft air conditioner, 8d battery, Onan and trailer hitch were
on mine. Did I miss anything? All are heavy items and enough weight to probably be detrimental to good
                  Too much weight and the tail starts to do more of the steering...... sounds familiar does'nt it ?
                  Onan cranks fine with full batteries up front but hav'nt tried it yet with low batteries. Don't
really care as I plan to be rid of it too, if the big 12v alternator and inverter system prove to be adequate.
                  Don Miller

Date: Fri, 16 Oct 1998 19:24:06 -0500
From: Al Ross <>
Subject: GMC: Battery blowup
Just a note of my recent experience so may prevent some one from making same mistake. My house battery
had run down while coach in the shop. Don't know why but immaterial. Not enough juice to start the generator.
I used the Battery Boost switch to connect power from the coach battery with the engine running to recharge
house battery. I waited a few minutes and hit the gen start switch. BANG! What a loud noise. Turns out the
battery was giving off hydrogen (I know I should have remembered) and starting the generator added the
appropriate spark to the hydrogen-oxygen. The result was a topless battery and acid everywhere. Fortunately it
was contained within the battery area next to the generator. I installed a new battery after the clean-up.
Hope this story helps prevent someone else from doing the same.
78 Royale

Date: Sat, 17 Oct 1998 11:14:21 EDT
Subject: Re: GMC: Battery blowup
In a message dated 10/17/98 2:13:53 AM Central Daylight Time, writes:
<< .

   One other possibility is that your battery was internally shorted or had a bad cell connector. This would
account for its going dead, and might provide an internal ignition source. That is to say: If it blew up, and the
cell caps were tight, it was probably junk anyways. :-)
I agree with you-------but then last week something happened that I had never seen before. My son called from
Walmart and said his battery had just blown up. I looked under the hood and sure enough the entire
top of the battery was blown off. There was no sign of fire no melted plastic no scorched paint-----nothing. The
battery was very low on water with some crud on the plates. My son said he just got in his truck
hit the key to start it and wham it blew. I looked at everything---could not see or smell anything to give me a
clue. Walmart would not change the battery----they said there must be another problem with the truck.
I checked the starter and wiring with a voltmeter could not see anything.
Bought a new battery-----been in for over a week now and everything is fine. I still dont have a clue as to what
Take Care

Date: Sat, 17 Oct 1998 16:55:02 +0100
From: "Donald W. Miller" <>
Subject: Re: GMC: House batteries

eventually - all electric - no propane - no Onan - rebuild project is still in progress.
I'll use a 165 amp Leece Neville alternator I happen to have on hand driven with double "V" belts. Leece
alternators are available up to 200 amps. I buy units rebuilt by "Arrow" from a parts house. Leece are used in
the trucking industry so are available from trucking sources too. Electrodyne builds brushless 12 volt alternators
up to 450 amps. Top grade and top price.
Prestolite - Leece and Electrodyne both have web sites for further info.
I installed a Statpower ProSine 2500 watt pure sine wave inverter which includes a top notch 100 amp charger.
I have used it enough to think highly of it. One very nice feature is it senses the GMC's total shorepower load
and automatically reduces battery charging to prevent tripping shorepower breakers.
Also have an 8 year old Trace 1500 watt which has been heavily used, seen thousands of sea miles, and never
given any trouble. IMO Trace products are excellent too.
Lessons learned so far:
1. If I had been thinking clearly when planning this installation I would have converted to a 24 volt system.
2. 2/0 welding cables from house battery to a 2500 watt inverter are best kept under 4 foot long.
3. At 2500 watts you better have an alternator on line or two golf cart batteries won't last long.
Don Miller

Date: Tue, 20 Oct 1998 01:41:36 +0100
From: "Donald W. Miller" <>
Subject: Re: GMC: House batteries
Eric - Alternator not yet installed. Just finished putting in inverter, batteries and heavy cables.
Will make new brackets and mount alternator where present alternator is It is larger but should fit OK.
Bought a new 3" double groove alternator pulley from a Leece dealer in Norfolk, Va.

Plan to use a matched pair of belts on two grooves to drive water pump, power steering pump and alternator.
The short power steering / water pump belt will be replaced with a belt identical to the one beside it which now
drives the alternator. BTW, on the boat I use industrial rather than automotive belts as they seem a better quality
with higher hp ratings.
Should have over 100 amps (1300 watts) with engine idling in neutral.
I took some 35mm pictures of the inverter mounted behind the refrigerator but have not finished the roll yet.
Will try to get some pix of the alternator too.
Don Miller
75 Glenbrook in pieces
Shenandoah Valley of Virginia

Don....I have been through this on my houseboat. In researching the concept, I came across a "formula" that, in
essence, lays out the bank size / inverter size relationship. In other words, my 2000 watt inverter/charger
"required" a minimum of 880 (reserve) amps of bank capacity. Three years of operation has led me to believe
the 880 amps is truly a "minimum". I will try to dig this information up. In may have been in one of Nigel
Calder's books, articles, or even in an old RV site, don't remember, but I will locate it. I would say that
2500 watts of inverter/charger will soon kill your bank, requiring replacement of the batteries. Larry Nelson PB

Date: Wed, 21 Oct 1998 02:04:01 +0100
From: "Donald W. Miller" <>
Subject: Re: GMC: House batteries

How right you are Larry, it takes big big batteries unless you are willing to keep an engine running.
We too lived aboard for several years in the extended cruising mode. A continuing problem is our decadent,
energy intensive, lifestyle. Need lots of ice cubes on hot days and gotta play with our electronics and powered
goodies. Another way of attacking the, "too small house battery problem", is to keep a big alternator on line
during times of high energy useage. In our case, it will be our 455 idling when not on shorepower.
I think I have most of Nigel Calder's books. Knows his stuff, does'nt he?
Thanks and cheers,
Don Miller
75 Glennbrook in bits and pieces
Shenandoah Valley of Virginia

Date: Thu, 22 Oct 1998 11:21:43 -0400
Subject: Re: GMC: House Batteys

Rob, Think about installing a pair of golf cart batteries. Great prices at Sam's club and they probably will last
longer than any regular automotive battery. IMHO!
    Dave Greenberg

On Thu, 22 Oct 1998 09:33:19 -0400 "robteed" <>

>Im going to buy some Batterys for the MH. Is a ACDELCO Sealed 1000/975 good for this? And
> should they be Deep Cycle batterys? What size are You guys running?
> Rob Teed

Date: Thu, 22 Oct 1998 11:32:07 -0400
From: "robteed" <>
Subject: RE: GMC: House Batteys

 Two up front? Also Use these to start the Coach? I plan to put a regular car battery in the Gen
 compartment. How much should I expect to pay for Golf cart Batterys?
 Rob Teed

Date: Thu, 22 Oct 1998 18:04:04 -0400
Subject: Re: GMC: House Batteys

Rob, you could put your golf carts up front as probably on your erly model this is whee the house battery was
located. Seems to me I paid $40-45 each at Sam's Club.

I would keep a separate battery for starting purposes. Golf Cart batterys are deep discharge types not a good
choice for a starting battery. Keep them isolated electrically so you don't draw down both battery banks at one
     Dave Greenberg

Date: Thu, 22 Oct 1998 18:32:34 -0400
From: "robteed" <>
Subject: RE: GMC: House Batteys

Thanks Dave,
 Sounds good. I have an older friend who has a bus. He told Me what to get. 1000/900 delco batterys. But
 they quit making them. I guess I'll try the golf cart batteries.
 Rob Teed
 74' Painted Desert

Date: Wed, 28 Oct 1998 05:06:28 EST
Subject: GMC: New biz + My Plan

1.      Here's an idea for a new business. Have someone sew up EXACT seat covers for the original equipment
seating (veranda, gaucho, dinette). These could be shipped via UPS and installed by an idiot. Any takers?

2.       Here's my plan on 12v power management. I have already installed two new golf cart batteries under the
gaucho. I already have a 700 watt inverter / 30a charger combo. These batteries will only supply the inverter,
which will be used "on the road" to supply the TV, via the existing 120v. house breaker. This bank will also
handle my ham radios. At this time, I will not interconnect this bank with the house bank in the slide out tray
next to the still-running-rough genset. I am replacing the two existing house 12v batteries currently in parallel
with two golf cart 6v in series. (I couldn't figure out the "current leak" in house bank, about 1.5 a. measured
from one of those house batteries. There was nothing on inside the coach, and no current flowing at the bus.
Then I pulled the battery tray all the way out, and measured the current where the cable leaves the battery
compartment - nothing! The culprit was one of the 12v batteries was putting a load on the other. DUH!
) BTW, I used a 12v amprobe to measure the current, very handy to have. I have already ordered the new
STatpower 40+ from West Marine, so out goes a (probably) very good converter for the flea market. (If I
provide a connection between the two banks, one charger will fool the other, and nothing will get done. At least
that has been my experience in the past.) The new under gaucho bank resides in a marine battery box.

Date: Wed, 28 Oct 1998 08:04:22, -0500
Subject: GMC: batt management

Sounds like you are doing the right stuff. There are a lot of old systems out there on GMC that are paralleling
battery banks with out isolators or switches. I just had a SOB friend buy two large 12 volt batt and was not
happy when I told him he was headed for problems like you had. I think this list has helped owners under
stand these configuration problems.
Gene 76Palm Beach /Or/CA

GMC Technical Information

Date: Tue, 8 Dec 1998 14:18:22, -0500
Subject: GMC: Inverters / single function

- -- [ From: Eugene Fisher * EMC.Ver #2.5.3 ] --
I would like to suggest another plan for providing battery powered AC (inverter) to the GMC. The complicated
110 VAC switching and wiring are probably not worth the effort.

I suggest that it would be better to buy several low power inverters that have their own power switches, AC
connectors, and place them at the point of need. I buy these 300 watt simulated sinewave- inverters for $20
from Frys' electronics in CA.

Buy one simulated sinewave inverter of the 1000 watt size, for the heavy loads.

If needed, buy a low power pure-sinewave inverter for the noise sensitive stereo.

Laptop (LT) computers charge an internal battery and do not require a clean power. I have used my Desk top
(DT) computer on a simulated sinewave inverter with no problems. However if you are concerned about the
power to your computer it is a relatively small load that could run on your stereo inverter.

                      SIM     SINE

Blender                 300   X
Can opener              100   X
Coffee Maker          1000    X
Drill 3/8"              500   X
Frying Pan             1000   X
Food mixer              300   X
Hair dryer             1000   X
Iron                   1000   X
Microwave              1000   X
Reading lamp            100   X
Television              700   X
Toaster               1500    X
Toaster over          1500    X
Vacuum cleaner        1000    X
VCR                      50   X
Stereo                  500   X
Computer (LT)           100   X
Computer (DT)           300   X
Soldering Iron        1000    X
Impact wrench         1000    X

From this list you can see you do not need to buy a $1500 sinewave inverter to run your $100 microwave. Most
of the AC loads in the Motor Home do not require pure sinewave power. The simulated sinewave inverters are
more than adequate for most of the loads and if they create RFI (radio frequency interference) noise turn the
invertors off when not in use. The 1000 watt inverters are typically on sale for $300 to $500.
Gene 76Palm Beach /Or/CA

Also, anyone have recommendations on the use (or avoidance) of sealed gel batteries on the inverter battery
bank? And lastly, my installer recommends the eventual upgrade of my alternator from the current 105 amp to
a rebuilt ambulance alternator.... 200 amp. Not sure if I want to go this far! Ideas?
I've been reading "Living on 12v". Not sure if this is the same as "Managing 12v".... Good stuff regardless...
Thanks all,
Greg Weber

Date: Wed, 09 Dec 1998 00:11:51 -0600

From: "mr.c" <>
Subject: Re: GMC: Inverters / single function

It was easy for me to put in my inverter and to run a line to the power control box and to find the two outlets I
needed to have with 120 v. The rest were left as original. I think it has worked for me without having lots of
inverters to connect up.

my .02c
Al Chernoff

>Also, anyone have recommendations on the use (or avoidance) of sealed gel batteries on the inverter battery

Providing that you have a charger that will handle them, they should work OK. I decided to use Golf Car
batteries because they have more history behind them as a bank of deep cycle batteries. And, they cost less per
standby AH.

And lastly, my installer recommends
>the eventual upgrade of my alternator from the current 105 amp to a rebuilt
>ambulance alternator.... 200 amp. Not sure if i want to go this far! Ideas?
>I've been reading "Living on 12v". Not sure if this is the same as "Managing
>12v".... Good stuff regardless...

Well, providing there's no other 12V loads, your 100 amp alternator will charge a 400 AH bank just fine if you
switch to a multi-stage regulator. So, I don't see that replacing the alternator really helps. With our existing 2
battery house bank, one hour of engine time will restore 50% of the charge quite well - with a different
regulator. If you are not going to replace the exiting regulator you definitely have no reason to switch
alternators. BTW, you want to make certain f you do switch to 200 amp alternator that it is rated for 200 amps
continuous duty. Many alternators are only rated for a fraction
of the quoted current load on a continuous basis.
Henry Davis Consulting, Inc / new product consulting

Date: Wed, 16 Dec 1998 17:46:30 -0800
Subject: GMC: Wal-Mart!

        The previous owner of My 73 Glacier was using 2 batteries wired parallel for spinning the 455 and a
single battery on the Onan. I don't like 2 batteries wired together without some manner of checking them
independently without having to disconnect the wiring. I also don't believe two should be required for cranking
if everythings working correctly.
        The idea I'm toying with is having 3 batteries available with solenoids controlled by dash toggles to shift
different batteries to different functions and TEMPORARILY parallel 2 (or even 3?) for short periods.
        Just an idea. No action yet.

73 Glacier
Pensacola, FL.

Date: Mon, 14 Dec 1998 20:07:18 -0800
From: Phil Swanson <>
Subject: Re: GMC: Inverters / single function

Gene, Does Fry's carry an inverter any higher that 300 watts? Can inverters be somehow wired in parellel to
provide more capacity at one point instead of having boxes all over your GMC?
                                 Phil Swanson

Date: Mon, 14 Dec 1998 23:19:22 EST
Subject: Re: GMC: Inverters / single function


Take a look at <A HREF="">Statpower Index Page</A>

Take Care

Date: Tue, 15 Dec 1998 08:44:21 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Inverters / single function

There is a good article in the Motorhome 1999 guide "Dingy towing Special' about the stat power 40+ and they
speak glowingly of it. I am in the process of looking for one this morning. The article convinced me.

Date: Tue, 15 Dec 1998 21:07:51 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: GMC: Statpower truecharger 40 smart charger

I am going to replace my 12 volt house charger in the coach and am coordinating with the Statpower people on
a price for a refurbished model 40. They have it down to $178 US so far and I think I can get lower prices
for multiple buys. the led remote readout is US $38 more.

Anyone interested in one if the price is right?

Tom & Marg Warner
Vernon Center NY

1976 palmbeach

From: Phil Swanson <>
Date: Tue, 15 Dec 1998 19:11:23 -0800
Subject: Re: GMC: Statpower truecharger 40 smart charger

Tom: You might check out their combination package if you are interested in an inverter along with the
Truecharge 40. For me, that's a better deal than just the charger. I do think that the 40+ isn't necessary for the
price difference unless you have 3 banks of batteries which the majority of us do not.
                                             Phil Swanson

Date: Tue, 15 Dec 1998 22:17:02, -0500
Subject: Re: GMC: Inverters / single function

No you cannot parallel the inverters. They would never be at the same phase and I think there would be lots of
arcing and sparking.

If you want just one, Al Chernoff makes the point that almost all of the AC circuits come to the AC breaker box
in the GMC and it is relatively easy to make a switching circuit. In this case would be best to buy a
large sinewave inverter. There are some great posts on my webpage that talk about how much battery power
you would need,.

My point was that most of my dry camping AC requirements are small and remote from each other. I have one
converter in the rear to charge batteries, One small one at the TV/drink stand for the TV and the computer, and
soon a 1000 watt under the rear bed to feed the Microwave. I think that is all I need when I don't use the Onan.
I am one of those that will always carry the 500 pound onan to run the air cond if we need to.

I like the multi inverters since they have their own switches and AC sockets , no new wires required.

So set your own requirements, the state of the art is good now and not that expensive.

good luck gene

Date: Tue, 15 Dec 1998 22:55:16 -0500
From: John Wright <>
Subject: Re: GMC: Statpower truecharger 40 smart charger

You would need the 40+ version which can three seperate batterys, the 40 can only charge a 2 battery system.

Date: Tue, 15 Dec 1998 23:58:39 -0600 (CST)

Subject: Re: GMC: Statpower truecharger 40 smart charger

I'm using the 40+ so that we have the three separate circuits. WE're a bit on the power hungry side right now.
When we change over to a 3-way fridge it hould get better. But then we'll be adding the PC and the budget
goes up.

Date: Wed, 16 Dec 1998 10:36:09 -0500
From: "Bartz, Paul" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger


What is the benefit of adding the battery charger, besides the obvious technology in today's units? Now you
have an another piece of equipment to deal with, in addition to your inverter.

Have you considered the Todd Power Source converter-charger ($260), an all in one unit sold by GMC owner
Byron Maxwell ( <> . He says it's the lowest cost of the three
"switching power supply" converters he knows of. Doesn't it make more sense to update your inverter-charger
with current state of the art equipment? Most original one's hum a lot.

 Paul Bartz

Date: Wed, 16 Dec 1998 13:31:41 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger

Go to the Statpower site at and look at the models. I like the statpower products and have
looked at both the statpower truecharge 40+ (written up in 1999 Motorhome) and the model 40 its predecessor.
In my estimation the truecharge 40 is an excellent charger without a couple of the bells and whistles of the 40+.
It will do everything we need for a big big reduction in price. the 40+ costs $460. I have negotiated the price
for the statpower truecharge 40 directly with Statpower and they are willing to give us a sizable discount if we
buy 9 units. the cost will be US $158 each plus approximately $12 for brokerage and shipping fees. the units
weigh about 8 3/4# each. We would have to add a UPS charge from my house to yours of about $9.00
depending on where you are located.

If anyone wants these units for that price I need a firm committment.

Date: Wed, 16 Dec 1998 14:12:19 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger

I have rethought the bulk buy of the statpower truecharge 40 models and now think that we would be making a
lot of work for ourselves by saving less than $10.each. We can buy the units direct from Statpower for CDN
269.95 which equals $175 US. In a bulk buy they want me to pay direct at an exchange rate that would equal
approx $158 each. when adding the various UPS rates from my house to yours it would bring it up to about
$168. for $7. each I think it is to much trouble. How would everyone feel about ordering the units direct from
Statpower at

Date: Wed, 16 Dec 1998 17:29:34 -0500
From: "Bartz, Paul" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger


Are you saying then that it is the battery charger portion of our original inverter that hums??? If not, then I
don't understand, because I thought two functions (i. e. inverter and charger) are in the original unit, but
handled electrically?????. Otherwise, if you just disconnect the battery charging capability from the original
inverter and substitute a new charger, you're still left with electrical hum.

As I understand the Statpower unit you're proposing, is solely a battery charger, right????

Am I missing something????


Date: Wed, 16 Dec 1998 15:59:46 -0700
From: (Dave Lowry)
Subject: GMC: Statpower truecharger 40 smart charger


I have 1 battery in back that is isolated for the generator, 1 up front to start the engine, and a pair of 6 volt golf
cart batteries (also up front) for the coach, and want to replace my OEM converter/charger. I'm pretty
sure I need the 40, rather than the 40+, but need to do a little more research to know for sure. Assuming I need
the 40, I'd be interested in a unit with the led monitor.
Dave Lowry, '76 Royale, Santa Barbara

Date: Wed, 16 Dec 1998 19:16:32 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Statpower truecharger 40 smart charger

Heinz that would probably be a better way to go as you are in a far better postion than I am being so close to the
company. They do have the other products you mentioned. I have been talking to Christine Berka,

<>, at 1-800-670-0707, extension 2177. I didn't realize until after I sent the e-mail to
everyone that it was more complicated than just ordering them and having them shipped to me. thought
NAFTA eliminated all of that.

UPS from washington state would definetly be the way to go.

The truecharger 40 comes in units of 3 to a case. Price for 3units, CDN 809.85, for 6 CDN 1538.72, for 9, CDN
2186.60. Remote LED panels are US $39.95 each.

would not be offended in the least if you would like to negotiate and finalize the deal.

I think the Statpower Truecharge 40 is an excellent replacement for the old ferroresonant charger in our
coaches. it has the advantage of smart charging our house battery to maximum charge and prevents sulfating of
Tom & Marg Warner
Vernon Center NY
1976 palmbeach

Date: Wed, 16 Dec 1998 19:18:04 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Statpower truecharger 40 smart charger

considering that the 40+ is now being quoted at $460 american I think it is a fantastic deal at about $158
Tom & Marg Warner
Vernon Center NY
1976 palmbeach

Date: Wed, 16 Dec 1998 19:18:57 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Fw: Statpower truecharger 40 smart charger

Most of it is hold overs from what Christine told me. New products that have scratches etc. They now only sell
the 40+

Tom & Marg Warner
Vernon Center NY
1976 palmbeach

Date: Wed, 16 Dec 1998 19:24:18 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger

No the original GMc had a 120 volt to 12 volt converter and battery charger. Its output is strictly 12 volts. The
statpower unit would replace it entirely

Tom & Marg Warner
Vernon Center NY
1976 palmbeach

Date: Wed, 16 Dec 1998 19:43:23 -0600 (CST)
Subject: GMC: Statpower truecharger 40 smart charger vs 40 plus

The TC 40 charges gel or flooded, deep-cycle lead acid batteries from 200-400 ampere-hrs. Includes
microprocessor control, 3 step charging, a battery chemistry selector switch, and 2 bank output.

The plus adds
1. battery type selections for sealed (gel), conventional flooded (wet), and Absorbed Glass Mat (AGM)
2. Additional control over the charging process: select 3-step (bulk/absorption/float) or 2-step
(bulk/absorption/off) depending on battery. Select 13.5 volt fixed to use as a pure DC power supply
3. optional automatic temperature compensation
4. equalization mode to help reduce sulfation
5. a 21 day cycle when connected to shore power to recharge batteries (top up) automatically
6. 3 banks instead of 2

1. The plus version is preferred if you are going to use AGM batteries. I chose wet batteries and could live
without the plus if I wanted to. There's no advantage there.
2. The additional control over the chraging process is nice but not required. I happen to like it since we use our
batteries very heavily.
3. OK. THis saves me from opening the electrical compartment door and flipping a switch.
4. This should extend the life of my batteries due to the deep discharge/charge cycles I use.
5. Well, I don't leave the coach sitting for this long. So, it's of little value
6. Split house, engine and a second (as yet not installed) house battery. The real reason I bought the 40+, but I
could have rigged mechanical switches. I wanted the convenience.

For the added cost you can afford to buy two sets of golf car batteries more than what the plus would require.

Do you need the additional features? I don't think so, unless you're a very heavy user of the house batteries.
Even then you can use the non-plus version just fine. Using an equalizer has its own set of issues that you have
to decide to handle. For example, halogen lights don't like the substantially higher voltage. Some electronics
may be damaged by the equalization charge. But it can extend the useful life of your batteries.

Without my particular set of requirements, I would have been more than happy with the straight 40.


Date: Wed, 16 Dec 1998 20:48:18 -0500
From: John Wright <>

Subject: Re: GMC: Statpower truecharger 40 smart charger
To do a 3 battery system you need the 40+, the 40 is for a 2 a battery system.

Date: Wed, 16 Dec 1998 23:29:46 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: Statpower truecharger 40 smart charger
         I believe that since the Onan has an alternator to charge its own isolated battery, the 2 bank charger
should be enough. The charger only has to charge the starting and house banks. The 3rd bank for the Onan
would not be connected to the charger at all and would rely on the Onan to charge it itself. This would also
avoid the problem that someone on the list reported about the Onan alternator kicking the Statpower out of
charge mode without having to modify the Onan.

Date: Wed, 16 Dec 1998 23:54:16, -0500
Subject: Re: GMC: Statpower truecharger 40 smart charger

You can read the post on my web page about how bad the Onan is as a charger, but it also shows you can do
away with the Onan bat and use the house bat to start it.

Date: Wed, 16 Dec 1998 21:26:24 -0700
From: Darren Paget <>
Subject: Re: GMC: Statpower truecharger 40 smart charger

By replacing the converter/charger with a charger only will make your entire 12v system run solely off the
battery. The stock system used your converter to change 110v to 12v thus bypassing your battery. The charger
system will keep your battery charged while it is plugged into shore power. Darren

Date: Thu, 17 Dec 1998 18:53:23 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Statpower truecharger 40 smart charger vs 40 plus

Dave, there seems to be some confusion relative to how 120 volt AC and 12 volts DC is used by the coach.
There was no 120 Volt AC INVERTER to change 12 volts DC to 120 volts AC on the coach as original
equipment. In addition there is no provision for you to "manually switch from shore power to generator when
maintaining my batteries from shore power instead of the engine's alternator" unless you are talking about
unplugging the external power cord from shore power and plugging it into the motor generator receptacle to

switch to generator power. I can't understand what you are doing here "if I've had the Onan running to provide
power to the A/C (the only thing I use the Onan for), I need to flip a couple of breakers before shore power will
charge the two 6v. coach batteries." There is no provision to do this in the original wiring for the coach.
I guess I am confused relative to how many batteries everyone has. I know that I only have 2, the auxiliary
battery next to the Onan, and the main battery. As a note, two golf batteries connected in series acting as the
auxiliary battery are considered one battery by the charger.

1. The coach can only get 120 volts AC from one source at a time either:

a. Shore power (the external power cord is unplugged from the motor generator receptacle and plugged into
shore power) or

b. The Onan generator(if the external power cord is left plugged into the motor generator receptacle)

2. You cannot get 120 volts AC from both sources at the same time.

3. Either 120 volt AC source (shore power or generator) supplies 120 volts AC to the air conditioner, water
heater and AC receptacles in the coach and also the 120 volt AC to 12 volt DC CONVERTER that supplies all
of the internal lights, furnace etc. This CONVERTER in turn also charges the auxiliary (living area) batter BUT
NOT THE MAIN (automotive) BATTERY. The isolation diodes on the engine firewall prevents that.

Now lets talk about the automotive battery. The alternator has a built in temperature sensitive charger to
independently charge both the house battery and the engine battery. It is able to do this because the output of
the alternator is split by the isolation diodes so that two independent outputs are provided to charge each one

The original converter does a poor job of charging the auxilary battery since it never puts our a high enough
voltage to get the battery up to a full charge (the alternator has to be running to do that) and has no
provision for a float charge. contrary to what several have said the statpower 40 will provide 12 volts DC
to the coach without drawing from the auxiliary battery if the load does not exceed 40 amps.

The optional remote LED panel indicates the charger status (float or charging), output in increasing amp
increments, and battery voltage in .3 volt increment. it costs $39.95

In my opinion the Statpower Truecharge 40 is a perfect replacement for our old technology ferroresonant
converter. In addition it has features that cost many hundreds of dollars more than the nearest competitor. It is
a steal in refurbished form for about $175. My coach only has two batteries and the 40+ would be of no
additional use to me.

Hope this clears up the misconceptions.

At 11:35 AM 12/17/98 -0700, you wrote:
>Thanks J. R.

>OK folks, let's see if I've got this straight; If I want the converter/charger to separately maintain all three
batteries (considering the 2 6v. batts. as one), I'll need the 40+. But if I only want it to maintain the coach and
starting batteries, I can get by with the 40 (not 40+). Here's my logic for possibly excluding the Onan's battery:
>1) The battery back at the generator is now charged by the Onan when it's running and/or the engine's
alternator when we're under way. If the Onan's battery should ever be run down the point it would not start the
Onan, I could always start the engine, and then start the Onan off the alternator.
>2) The Statpower could be wired to maintain both the house and starting batteries as well as provide clean 12
volt power whenever we're plugged into shore power.
>Here's my current situation: I live in Santa Barbara (no freezing). My coach run up to full operating
temperature at least once every 6 weeks. I am plugged in to shore power whenever the coach is at home.
>I understand that the Statpower 40 will do a better job of maintaining my house and engine batteries. But will
it also automatically switch between shore power and generator power as the source of power to the converter
and A/C, instead of our having to do it manually? I've checked the Statpower internet page, but can't find details
on the 40 (not 40+).
>Hope I've clearly stated my questions.
>Dave Lowry, '76 Royale, Santa Barbara
Tom & Marg Warner
Vernon Center NY
1976 palmbeach

Date: Thu, 17 Dec 1998 18:31:32 -0800
From: "Heinz Wittenbecher" <>
Subject: Re: GMC: Statpower 40 / Shore/genset switchover


Jim sells a switchover relay that has a built-in time delay, i.e. it gives enough time for the genset to come up to
speed and then switches the coach from shore to genset.

Easy to wire up. Basically the relay selects input for the main fuse box.

Get the 30 amp one. (There is also a 50 amp but it's big)

I have that setup in my Transmode but the delay went out so I used the delay circuit board from the setup I got
from Jim. Of course shortly afterwards the genset gave up altogether but that's another (unrelated) story.

With ref to a new GenSet I'm still hoping that Jim is making progress on an upgrade kit for the newer Onan.
**** Jim, you listening ??? *** :-)

'76 Transmode

Date: Fri, 18 Dec 1998 12:29:35 -0500
From: "Bartz, Paul" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger


What you said was what I was trying to point out and the fallacy that I see with replacing the original converter
by installing a charger. I know that today's units offer clean 12 v power whether from either 12 v (battery) or a
120 v converter systems.

However, beyond that, what advantage(s) are there to going with a charger type unit vs. a modern converter that
efficiently charges and is also capable of producing "clean" 12 v power?

  Paul Bartz

From: Darren Paget []
Sent: Wednesday, December 16, 1998 11:26 PM
Subject:     Re: GMC: Statpower truecharger 40 smart charger

By replacing the converter/charger with a charger only will make your entire 12v system run solely off the
battery. The stock system used your converter to change 110v to 12v thus bypassing your battery. The charger
system will keep your battery charged while it is plugged into shore power. Darren

From: Thomas G. Warner []
Sent: Wednesday, December 16, 1998 11:58 AM
Subject:        RE: GMC: Statpower truecharger 40 smart charger
This one replaces the one that hums and has the latest technology.
 At 10:36 AM 12/16/98 -0500, you wrote:
What is the benefit of adding the battery charger, besides the obvious technology in today's units? Now you
have an another piece of equipment to deal with, in addition to your inverter. Have you considered the Todd
Power Source converter-charger ($260), an all in one unit sold by GMC owner Byron Maxwell
( <> ) He says it's the lowest cost of the three
"switching power supply" converters he knows of. Doesn't it make more sense to update your inverter-charger
with current state of the art equipment? Most original one's hum a lot.
  Paul Bartz

Date: Fri, 18 Dec 1998 13:44:05 EST
Subject: Re: GMC: inverter cable size

Just bought a Statpower ProSine 1800 inverter, which looks like a nice quality piece. One problem however.
My electronically-inclined friend who advised and assisted me on the install bought 4-gauge cable for the (2)
10-foot runs from the battery: one positive, one negative. Whenever i power-on my 110v stereo amplifier,
which is rated for 220 watts, the start-up surge is putting the inverter into reset mode. The inverter is rated for
surges up to 2900 watts. Statpower tech support is saying that the 4 gauge cable is the problem, since the
recommended cable for a 10-foot run would be #0/4!! To every electronically-inclined person i speak to, this
sounds like overkill, since the voltage loss due to using 4 gauge cable is pretty minor on a 10 foot run, and
certainly not enough to make the 12 volts die down to 10.5v, which would trigger a reset on this inverter, but
perhaps this inverter is even more sensitive than the manufacture cares to admit (?). #0/4 cable thickness seems
ridiculous, and not very easy to run thru the living compartment, and then thru the firewall.
Anybody using inverters of this size have any recommendations on what might be a happy-medium cable size
to use, between #4 and #0/4?
Of course tech support knows what's "best" for their products, but often the overkill factor just seems a bit
Any suggestions appreciated.
Greg Weber
'78 Eleganza II

Date: Fri, 18 Dec 1998 13:53:46 -0500
From: Patrick Flowers <>
Subject: Re: GMC: inverter cable size


Might not be the answer your looking for, but I understand you're much better off to mount the inverter near the
batteries and use short DC cable runs. This might make your AC wiring more complicated, but it's the best way
to go. That's why most people put golf cart batteries in the generator compartment and the inverter next to the
AC breaker panel.

As far as your electronics expert, keep in mind that handling large amounts of DC current is a different animal.
Go with the manufacturer's rec's.


Date: Fri, 18 Dec 1998 16:36:00 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger

Maybe I did not explain it clearly. the statpower Truecharge 40 is a converter. it not only charges the batteries
but produces 12V DC for the coach. It totally replaces the old converter and retains all of the original functions
plus more.

Tom & Marg Warner
Vernon Center NY
1976 palmbeach

Date: Fri, 18 Dec 1998 17:32:42 EST
Subject: GMC: Whether you think you can or think you can't-- you're right! Go-OFART

Hi Gmc!

   I went out and bought stock in Statpower today. I thought if I bought stock, I might be able to understand
what was being talked about. I made another web page last night of my GMC. Lots of pictures, someday I'll
get good at it and make the thumbnails work! Any how to's would be appreciated. <A
HREF="">GMC PHOTOS 12/16/98 </A>


Date: Fri, 18 Dec 1998 19:30:48 -0700
From: Darren Paget <>
Subject: Re: GMC: Statpower truecharger 40 smart charger

My understanding is, and I may be wrong, that by using a good quality stand alone charger is the best way to
keep your coach batteries in top shape. Most charger/converters will "gas your batteries". Meaning that there is
no staged charge. The charger/converter will keep charging at an accelerated rate with no "float charge". Most
c/c will give a constant charge of 16v which over a long period of time, i.e.. boondocking, will evaporate the
water out of your battery, (gassing). By having, only, a charger this will give your battery a three stage charge.
Bulk charge @ 14.5v. Absorption charge @ 13.75v. Float charge @ 13.4v. The other nice thing about most
inverter/chargers is that they are programmable to your specific battery or configuration. This info. refers
specifically to TRACE INVERTERS but is applicable to others. Darren

Date: Fri, 18 Dec 1998 23:17:27 EST
Subject: Re: GMC: Statpower truecharger 40 smart charger


The problem here is that the Stat unit is good for 40 amps. It will put it where it is needed. If you are using 10
amps in the coach it will only charge 30 amps. On almost all converters they only have a 3 amp charger and
supply 30 to 50 amps to the coach. If you want to charge your house battery while you are boondocking it

will take for ever. With the Stat unit turn off everything in the coach and you will be charging your batteries
with 40 amps not 3. You can bring back a 2 golf cart house battery system in about 2 hours. Not the all day run
with the 3 amp charger or running the 455 engine for 1 to 1 1/2 hours. I hope this clears up some of the
problems we seem to be having here. If not holler I will try harder.
Take Care

Date: Fri, 18 Dec 1998 23:20:53 -0500
From: "Mark Grady" <>
Subject: GMC: inverter cable size (reply)

> I think you will only be drawing 18 amps. 1800 watts / 110 volts
> = < 18 amps
> Darren

Assuming 100% efficiency of the inverter. Can't happen. 80-85% maybe.

Check the mfgs specs for current draw at rated voltage, and then remember,
voltage goes down, amps go up.

Mark Grady

Date: Fri, 18 Dec 1998 23:34:19 EST
Subject: Re: GMC: Wal-Mart!
One good battery will crank the 455 if it and the starter are okay. IF you have the right starter-a high torque

Date: Fri, 18 Dec 1998 23:37:11 EST
Subject: Re: GMC: inverter cable size
Herein lies the problem!!! You are quite correct in your formula. The problem is it is the wrong formula. 1800
watts / 100 volts= 18. The problem is to get 18 amps of 120 volts you must do this. Watts = amps x volts.
To get 18 amps of 120 volts from 12 volts you must multiply by 10. With this formula you need 180 amps of 12
volts. I would say that with the loss of the inverter this is probably closer than my pure formula earlier. Again
aint no 4 gauge wire going to handle that. Thats what I figure.

Take Care

Date: Fri, 18 Dec 1998 23:23:57 -0600
From: "William D. Minor" <>
Subject: GMC: Statpower TRUECharge 40 Smart Charger

Just a short note:

I am replacing my 40 amp inverter (which only had a 3 amp charging rate) with the 40 amp Statpower as we
speak. The initial test went very well. The Truecharger supplied 40 amps to the Coach and generator batteries
for about 10 minutes, and then went into the absorbsion mode. My coach hasn't been on shorepower for about a
month (electric refrigerator was turned off, so I had no loads). The 40 amp inverter wouldn't charge the
batteries quickly enough while dry-camping, and would overcharge the batteries if left on (voltage reading
above 15 volts). The Truecharger kept a constant 14.2 volts even with all lights on and using the recirc tiolet.
BUT it is not as quiet as we have been led to believe, at least not when charging at the higher rates (20 amps
and up) because of the cooling fan. The fan does, however, shutdown in the lower ranges.

I'm going to install the remote monitoring panel ($30 @ West Marine) tomorrow, and will let You know how it
goes, but so far this is a BIG improvement over the OEM converter, and only 1/2 the price (even with
shipping) of the 40+.

Bill Minor
'73 GMC 230 Sequoia
Waukegan, Illinois

Date: Sat, 19 Dec 1998 11:21:37 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: inverter cable size (reply)

the weak point in the converter Mark is the DC side not the AC as you noted. We can all pull up to 50 amps AC
thru our external power cord, or using the generator. However when you are working with a converter that
converts 120volts AC to 12 volts DC problems quickly appear because of the resistance in the toal DC circuit.

The relationship between voltage and amperage is not exactly like you described. The proper relationship is:
Current = voltage/resistance, and power = current squared X resistance. Using these relationships we can see
that it is the total resistance in the circuit that determines the current draw. The voltage out of the battery is
determind for the most part by the internal resistance of the cells.

Since the resistance of the circuit is the critical factor and since we cannot change the internal resistance of the
battery (short of replacing the battery) and the internal resistance of the converter(it is determined by
the manufacturer), we can see that the resistance between the battery terminals and the input to the converter is
the critical factor.

Most designers I believe say that there should be no more than a 1/2 volt drop between the battery and the input
to the converter.

The resistance of this cable link than is determined by two things, material and length. copper has a lower
resistance per cross sectional area than aluminum so we should use copper, and use stranded copper not solid.

If one remembers that our engine starters draw between 65-90 amps no load, than one can quickly see that we
are asking a lot from our converters when running 100 amps (1200Watts) from our house batteries. They just
were not designed to do that for long.

Look at your cable running from the house battery to the front of the coach (0#) and use one like it for the cable
between the battery and the converter. a 4 gauge wire will not work unless you want to melt it.

Frank I took it for granted that everyone knew that since I was replacing
the old charger.inverter, the Truecharge 40 accomplished the same function.

Date: Tue, 22 Dec 1998 15:48:48 -0500
From: "Bartz, Paul" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger

I went back and read Wes Coughlin's article on the Truecharge 40+ in the Sep 98/Issue 17, GMC Motorhome
News (Cinnabar) newsletter and see where that model is needed if you want to maintain more than two coach
batteries (I have three in my 78 Royale).

There are times when a coach is not used for weeks or months at a time. Keeping batteries, including the engine
battery, at their optimal state of charge is important to their longevity. This is where the new generation of
chargers, such as the Statpower Truecharge 40/Truecharge 40+ series, shine with their 21-day maintenance
cycle, according to Wes's article. All one needs to do to take advantage of the cycle, is be plugged into shore
power. The battery "boiling" phenomena resulting from being plugged in is no longer a concern with unit's such
as Statpower's.

IMO, it would be beneficial to use a unit that is configured to connect to ALL of the coach batteries.

In my case, although the price for the former refurbished unit is attractive from Statpower, it only supports a
maximum of two batteries, and therefore I need their later unit.

Don't know if anyone thought of it or not, but it seems to me that there is an economic savings (not to mention
the convenience of always having charged batteries), to stretching out the life cycle of our batteries by replacing
our original ferroresonant converter - charger with a modern day "charger". Doing so also eliminates the humm
associated with the original units, as well as the audio interference associated with using a 12 v powered TV or
stereo equipment. All of these benefits are not available when using individual inverter units.

Incidentally, in my research I noted from Statpower's web site that Foretravel has recently changed over to the
Statpower PROsine 2.5 inverter exclusively for their coaches. I talked to Foretravel's electrical engineer
the other day and he tells me the reliability of Statpower's units is superior to what they previously utilized.

 Paul Bartz.

From: Thomas G. Warner []
Sent: Friday, December 18, 1998 8:32 AM
Subject:      Re: GMC: Statpower truecharger 40 smart charger

I would use the 40 in this situration. You do not have to charge the engine battery with this set up so the two
banks of the 40 would service your generator battery and the 2 golf batteries

Date: Tue, 22 Dec 1998 16:20:19 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger

Paul there seems to be some confusion relative to what the Truecharge 40 will do. It will replace the old
ferroresonant unit(original equipment). It will support two battery BANKS(not batteries) simultaneously. That
means it will service 2 golf batteries connected in series, or one large 12V battery (1 bank) for the house battery,
and one other battery bank. The majority of GMC coaches have just 2 battery banks. The house
battery(installed near the generator) and the engine battery (installed on the passenger side front of
the coach). All we really need is a charger for one battery bank since the alternator services the engine battery.
Hope that this clarifies the issue.

I can't really see where we need the 40+ unit. It is overkill for our use, unless we just want to spend money on
the latest technology.

Date: Tue, 22 Dec 1998 16:42:50 -0500
From: "Bartz, Paul" <>
Subject: RE: GMC: Statpower truecharger 40 smart charger


I agree that the alternator will charge the engine battery, but only when the engine is running, and don't deny
that a number of coaches may have only two batteries. However, in my case, as I mentioned, I have three
batteries, one of which is the engine battery.

I'm not advocating that everyone needs the Truecharge 40+, but I feel I do because of having three batteries.

My original point was that there are frequently times when a coach is not used for weeks or months and the
engine battery still needs to be or should be "maintained" for greatest longevity. Therefore, I don't agree that
the maximum benefits are obtained if the engine battery isn't hooked up to a Truecharge type unit. On the other
hand, it's up to each individual to determine their own configuration.

I was merely trying to point out the benefits, as I see them, of connecting "ALL" coach batteries to a modern
day "charger".


Date: Tue, 22 Dec 1998 17:38:08 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: How many batteries in your coaches?

I have never seen a GMC motorhome with more than 2 battery banks, although I am aware that it is possible.
What you say is may be true, however it would depend on how your batteries are used, what type they are, and
where they are mounted?

There is a big difference between the two kinds of batteries. The house battery is a deep cycle battery and is
capable of giving smaller amounts of current for a long period of time, and it does not function well as a
starting battery, or when drawing large amounts of current . The engine battery on the other hand is selected for
drawing large amounts of current for a short period of time, ie; starting the engine.

Bottom line is that if you have more than 2 battery banks you need the 40+.

How many people that monitor this net have more than 2 batteries in their coaches?

Date: Tue, 22 Dec 1998 17:57:51 -0500
From: Zachary Zehnacker <>
Subject: RE: GMC: How many batteries in your coaches?
We have only 2 banks, but we have 3 batteries in the house bank and 1 in the starting bank. They are all 12 volt
deep cycle/starting, and the house batteries are all in parallel. Apparently many people have the Onan battery as
a separate bank to ensure that the Onan will always have a good battery. Our generator (Honda) draws off the
house bank (though the starting battery probably would be better). We would prefer a higher amp capability,
but we are seriously considering the 40 because of its good features and low price.

I was wondering if the 40 has the 21 day cycle like the 40+. This seems like a feature that would be nice to
have for the winter months when the GMC rarely gets used, although probably not worth the >$200 difference
between the 40 and 40+.

Date: Tue, 22 Dec 1998 18:42:11 EST
Subject: Re: GMC: RE: engine battery charge maintenance

About a year ago I bought a small trickle charge unit from Campers World which keeps the battery topped off
and will not boil or overcharge the battery. It was approx. $39.00. I ran the wire from the power unit (about the
size of a calculator transformer) through the right (passenger side) into the passenger compartment side of the
door beneath the windshield, put one wire to the stud that goes to the engine battery and grounded the other.
When I store the motorhome I plug the unit into the 110v outlet by the dinette. I had a parasitic current draw
before that would drain the battery within about 2 or 3 weeks (probably the radio). Now the battery stays up.
This is a lot cheaper alternative to going from a Statpower 40 to the 40+ just to maintain the engine battery.

Emery Stora
77 Kingsley
Santa Fe, NM

Date: Tue, 22 Dec 1998 18:50:33 EST
Subject: Re: GMC: RE: How many batteries in your coaches?

I hope that the three house batteries that you say are in parallel are separated by battery isolators because you
should never put batteries in parallel by just connecting their terminals. First, they will only charge up
to the capacity of the weakest battery; secondly, if you get a shorted cell in one battery it will most likely ruin
the other batteries.

The typical GMC has two banks with either a single 12v or two 6 v in series for the house bank and one 12 v.
for the engine battery. The two banks are isolated so as to allow the engine alternator to charge both to the full
capacity of both banks, but not to allow the engine or the house bank to drain the other (unless the booster
switch is pushed).

Emery Stora
77 Kingsley
Santa Fe, NM

Date: Tue, 22 Dec 1998 20:34:25 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: How many batteries in your coaches?
The batteries are not isolated. We know it is not the ideal situation, but we seem to get pretty good life out of
the batteries anyway. We like the extra capacity. It would cost enough extra to get the two big 6V batteries
needed for the same capacity, that we can change the cheaper and easier to get 12V batteries much more often.
We also replace all the batteries at the same time and get all of the same type. This way, any differences
between the best and worst battery capacities should be small. Since we would probably change both 6V
batteries at the same time as well if any problems developed, it really doesn't matter if one 12V battery kills the
other 12V batteries. They would all get changed whether they needed it or not anyway.

Date: Tue, 22 Dec 1998 22:49:48 -0600
From: "William D. Minor" <>
Subject: Re: GMC: Battery Banks

I have 3 battery banks in my '73 Sequoia. My Generator battery used to be in parallel with my house battery,
but I isolated the generator battery by using the old alternator isolator when I replaced it with a
higher amperage unit. This way my generator always has a good battery for starting, and the engine can do a
pretty good job of charging the generator battery as well as the coach and house batteries. My TRUEcharger 40

charges the Generator and House batteries. I don't believe I need the TRUEcharger connected to the coach
battery, but if i ever do I'll probably connect it through the aforementioned isolator.
Bill Minor
'73 GMC 230 Sequoia
Waukegan, Illinois

Date: Wed, 23 Dec 1998 21:30:01 EST
Subject: Re: GMC: How many batteries in your coaches?
Thermal Oil Batteries are a lead-acid battery with a some kind of oil on top of the water.They say they don`t
vent and don`t cause corrosion. What sold me was they recover after being discharged without being charged.I
had heard about them about 10 years ago but I never bought any.I found them in the yellow pages under
batteries (Thermal Oil Battery) I have size 27 deep cycle,they are heavier than the size 27 deep cycle batteries
that I replaced.I paid $73.00 each.
  At thanksgiving we dry camped at Dillon Beach, Ca. over Thanksgiving for 7 days and we used the heater
some the mornings and they did ok, time will tell.In the 11 years I have owned the GMC we have camped with
hookups about 12-15 times.
   Mike P.
   Central Ca.
   74 Canyon Lands

Date: Wed, 23 Dec 1998 09:12:16 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: RE: GMC: How many batteries in your coaches?

Zak the 40 has the 21 day feature. As far as I can tell from talking to Statpower the only real difference is that
the 40+ will act as a 12 volt DC power supply without being hooked up to a battery. Since ours will replace
the original converter and be permanently attached to the house battery seems like no advantage to me.

I am interested in how your house batteries are connected? 2 six volt batteries in series and one 12volt in
parallel with them?

Date: Wed, 23 Dec 1998 15:06:21 -0700
From: "Richard Guthart" <>
Subject: Re: GMC: How many batteries in your coaches?
Yup, exactly. Most of the places we like to go for weekends in the Rocky Mountains do not have shore power,
and it's disruptive to neighbors to run the generator. There's room for two batteries up front under the
passenger's toes and one on the driver's side, just behind the steering gear. Besides, I figured I could use the
added up-front weight for traction.

Date: Thu, 24 Dec 1998 12:30:38 -0700
From: (Dave Lowry)
Subject: GMC: Batteries

We also have 3 battery banks. Up front on the right side are a 12 automotive battery to start the engine, and
behind it are two 6v. deep cycle golf cart batteries, wired in series to make 12v., to supply the "house". At the
back is a 12 automotive battery to start the generator. The alternator charges all of them when we're under way,
and each bank is isolated from the other so that we can only drain one bank at a time.

TRY THIS: Run the dash stereo and the CB off the house batteries so you can run them while camped without
draining the starting battery, and to reduce electrical interference while under way.

Also, I ordered the reconditioned StatPower 40 and the remote panel yesterday. I'll have it wired up to charge
the "house" and "starter" battery banks. The generator can charge its own battery, and if it's low, we need only
fire up the 455 and then start the generator. We rarely dry camp for more than 2 nights in a row, but when we
do, we'll just start up the trusty Onan (one way or another) for a couple of hours and be set for another day or

Happy holidays to all you terrific GMCnetters and your familys.
Dave Lowry, '76 Royale, Santa Barbara

Date: Thu, 24 Dec 1998 16:57:02 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Batteries
I got my remote power panel for the statpower today. very nice display. Shows voltage for each bank and the
charging current being used.

Date: Sat, 26 Dec 1998 07:47:20 -0700
From: "Richard Guthart" <>
Subject: GMC: Statpower

Hey guys, I just discovered something about the Statpower. It charges when connected to shorepower but not
when I run the Onan genset.

This is because the genset starter, in my coach at least, is wired to the house battery bank and the Onan's little
10-amp alternator charges that battery bank whenever the Onan is running. The Statpower is smart enough to
sense that, and sits in stand-by mode.

Now I am wondering, can I disconnect the Onan alternator output wire without hurting anything on the Onan?
According to the wiring diagram it connects to the "bat" terminal on the Onan starter solenoid. Also, there are
several wires to that terminal, 3 I think. Which one to disconnect?

Date: Sun, 27 Dec 1998 01:52:18 EST
From: (duane m simmons)
Subject: Re: GMC: GMC Motorhome Digest V2 #171

Richard Guthart/Frank SW Indiana
I did post a reply pertaining to the smart chargers being fooled by the Onan Voltage Regulator (VR) output.
Most Onan VR don't work anyway, not required & become a problem by loading down the Flywheel Alternator
to the point that it will not achieve it's primary signal to identify that the Onan is running.
Best to remove the wires from the VR & tape them up (maintain the common connected wires as common). All
Onans are not wired identical, however, most have 3 wires attached to the VR. One is by itself & 2 are
common on 1 VR terminal. After removing the wires, tape up the single wire by itself & keep the two wires
together & tape them up if so configured. The only time the Onan VR is required is for some of the early
coaches that had a small dedicated battery for the Onan start battery. The only was to charge that dedicated
battery was via the Onan VR. At best the VR output is 2 amperes maximum. Cannot be the 10 amperes as
advertized (charges thru a 5 ampere fuse). Most early coaches have been upgraded to a common house & Onan
battery in the rear. Two 6 volt Golf Cart batteries makes one 12v battery pack via wire connection (series
connection...the + & - leads are connected together).
Hope this helps !!!

Happy GMCing
Duane Simmons

Date: Sun, 27 Dec 1998 00:02:56 -0500
From: "Edgar T. Kremer" <>
Subject: Re: GMC: Batteries
Power for the above can be tapped off the BATTERY BOOST switch. If the house battery voltage does not
connect to the battery boost switch, it is a simple mod. This will also allow you to tie house & engine batteries
together (boost) regardless of which one is dead.

Date: Wed, 10 Jun 1998 09:56:35 -0700
From: "Heinz Wittenbecher" <>
Subject: Power Inverters
As the recent topic(s) have included onboard computing power, clean power is essential.
I've been using (abusing) a 1200watt HeartInterface inverter for over 10 years. It's on constantly as I have added
powerbars, etc that I run the computers with, i.e. built-in circuits that are inverted 110V.
If you'r thinking inverter, I would recommend DO NOT get an inverter/charger combination unless there is a
manual switch-over mode. If it switches on sensing AC you will not be on inverter when GenSet is running or
shorepower in use... and that's when you want it most of all :-) To keep the coach battery charged I use 2
30amp solid state chargers purchased moons ago from Caspro. These chargers replace the trickle
charger/converter that is part of the coach. I simply unplugged it.
A note re powerbars. If you're using a powerbar downstream of the inverter use a PLAIN powerbar, i.e. no built
in surge suppression.
Throwin' it out there for what it's worth :-)
Heinz '76 Transmode

Date: Sun, 13 Dec 1998 21:01:52, -0500
Subject: Re: GMC: Inverters / single function

It looks like some of the format was lost on the table I tried to send. The only two loads that might require a
pure sinewave inverter were the Desktop computer and the Stereo system. Al Chernoff has shown me that his
batt/AC television actually works better on the simulated sinewave inverter than it does on DC. He says the
VCR has more motor power and works faster. The Color is excellent and does not have noise from the

I have used my Desktop computer on the simulated sinewave inverter and it also works well.

I do not have a great stereo in my GMC yet so I guess I will wait to get a sine wave inverter.

Thanks for asking

- -------- REPLY, Original message follows --------

Date: Saturday, 12-Dec-98 11:07 PM

From: Phil Swanson           \ Internet: (
To: gmclist             \ Internet: (gmcmotorhome@mailinglists

Attachment: mimemsg.doc Code: 028OFBC \ Created: Unknown [3 Kb]

Subject: Re: GMC: Inverters / single function

   Gene, Isn't your statement about the microwave in direct conflict with your list? Looks to me like you have
the sinewave as a requirement for the microwave? Also, what happens if you run a color TV on a simulated
sine wave type? Is there allot of picture interference or??

                            Phil Swanson

Date: Wed, 30 Dec 1998 10:04:11 -0800
From: "Tipton, Eric" <>
Subject: RE: GMC: How many batteries in your coaches?

I have the same configuration with three 12 volt size 24 deep cycle house batteries in the gen compartment. I
know that most large bus type rigs run multiple house batteries in parallel. I have been toying with the idea of
going to two six volt golf cart batteries because I have been told that a parallel bank is not a good idea. The

theory or reality is that if one cell in the bank is weak then it will drain all of the others. I would appreciate you
Eric Tipton

Date: Wed, 30 Dec 1998 12:57:25, -0500
Subject: RE: GMC: How many batteries in your coaches?

There is a little more than that, the Golf batts have a better discharge curve for house type applications. You
can read about this on the web page.

Subject: RE: GMC: How many batteries in your coaches?
I have the same configuration with three 12 volt size 24 deep cycle house batteries in the gen compartment. I
know that most large bus type rigs run multiple house batteries in parallel. I have been toying with the idea of
going to two six volt golf cart batteries because I have been told that a parallel bank is not a good idea. The
theory or reality is that if one cell in the bank is weak then it will drain all of the others. I would appreciate you
thoughts. Thanks
  Eric Tipton

Date: Thu, 31 Dec 1998 23:13:54 EST
Subject: GMC: Batteries - care and feeding

Since there have been many questions on batteries lately you might want to check out this on the WWW.
More than you probably want to know about batteries.
Emery Stora
77 Kingsley
Santa Fe, NM

  I keep a cheap little voltage monitor (cigarette lighter plug with colored LEDs) plugged in up front when
camping/travelling. This "displays" the engine battery voltage, which can then be compared with the house
batteries' voltage at the monitor panel. When camping, the house bateries should go down, but not the engine
  Works for me. (Did I mention it's cheap????)

Rick Staples
'75 Eleganza
Louisville, CO

Date: Mon, 18 Jan 1999 16:41:17 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Statpower (follow up question)

I ordered the 40 since it will do everything that I want and more. You can use the remote temp sensor but I
concluded that it is not necessay. The statpower 40 has a 3 way switch on the unit to set the temp range, cold,
warm, hot I believe.

I have one large battery but the statpower will do the same job if you have 2 6volt batteries in series.

Date: Wed, 20 Jan 1999 11:29:01 -0500
From: "Ralph D. Edelbach" <edelbach@TCNJ.EDU>
Subject: GMC: Battery specs

Here is some info that I thought was interesting and might prove useful at some time. It was in a brochure that I
picked up from the Interstate Batteries booth at the Atlantic City Power Boat Show.

Volts         Specific        %
             Gravity       Charge
- ------------------------------------
12.66         1.265        100 %

12.45        1.225          75 %

12.25        1.190          50 %

12.05        1.145          25 %

11.90        1.100            0%

Ralph Edelbach, '74 Glacier

Date: Thu, 21 Jan 1999 00:16:49, -0500
Subject: GMC: Replace the battery diode isolator

The number of holes indicated my diode isolator has been replaced 3 times. So here is a new approach.

The Battery Combiner (BC) replaces the Diode Isolator provided with the GMC.
When either the alternator or the battery charger is detected (13.1 volts), the Combiner connects the Starter
battery and the House battery in parallel . When the battery voltage drops to 12.8 volts (off the charger) the
Combiner releases.

The features are:
     1 No one half volt drop in the charging voltages-- allows full charge.
     2 Automatically senses the charger, shore power or alternator
     3 Disconnects when the chargers stop
     4 Only draws .1 ma when the chargers are in operation
     5 Maintains both batteries charge.

The circuit is up on the web page
- --
Gene 76 Palm Beach /Or/CA

Date: Thu, 21 Jan 1999 20:23:12 -0800
From: Phil Stewart <>
Subject: Re: GMC: Replace the battery diode isolator
I often wondered why the RV industry never embraced the battery combiners over the diode isolators because
as you point out there appear to be several factors in their favor:

The marine industry uses the combiners I believe because major suppliers like West Marine sell several models
and extoll their virtues. So, can anyone share what the disadvantages of combiners are when compared to the
stock diode isolators we have in our GMCs?
Phil Stewart
'76 Transmode, TN

Date: Thu, 21 Jan 1999 23:31:37 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: Replace the battery diode isolator
High amp solenoid relays were not that reliable for many years unless they were very expensive. I would have
to think that reliability and cost are probably among the major reasons that these battery combiners have not
been more popular in the RV industry. A diode isolator has no mechanical parts and should last forever if
operated below its rated capabilities. A battery combiner (of the relay type at least) has mechanical parts which
are probably more likely to fail. They are also often rated for lower currents than the isolators. We have a high
amp alternator which can put out more amps than the continuous rating of the battery combiner mentioned here.

A cheap isolator, on the other hand, is rated for the high amps and has worked for several years with no

Another thought is the idea of 12V batteries in parallel. That seems to be basically what the battery combiner
does. It is only when a charge is being applied, but if one battery dies suddenly, the other would probably be
affected as well. The isolator seems to keep the two banks more separated, so maybe it would not be such a
problem. Anyone have any thoughts on this?

Current draw might be another consideration. If solenoid relays are used, there would be some current draw.
The very small (30-40 amp rated though) automotive type relays we have used draw at least 1 mA. Assuming
that a solenoid like the one used in the GMC battery booster switch is used in these battery combiners, I would
think that the current draw would be quite a bit higher (.1 A or so). The stats listed below indicate a current
draw of only .1 mA though. Do they use something other than a solenoid relay to connect the batteries, or
should it have been .1 A. Even .1 A would be better than the voltage drop the isolator causes though, so this
idea is probably not very valid.

Overall, IMO cost is probably the biggest factor. Looking at all the high dollar stuff in the West Marine catalog
and stores, I think that average boaters might spend even more on their boats than average RVers spend on their
RVs (yes even GMCers :). This may help explain the difference in popularity of the more expensive battery
combiner when RVers and boaters are compared. For an example, just take a look at which catalog has the
$400 Statpower converter/charger. West Marine carries it, and ,IIRC, even has a version with their name on it.
I assume that they have carried this type of converter/charger for many years, while the RV industry seems to be
switching over only recently. Most of the RV catalogs still only offer old style convertors or possibly cheap
new style ones. I don't expect a "Camping World" version of any $400 convertor/chargers any time soon :).
Each market carries what they think they can sell. This is why we have to look around at many different
stores/markets if we want to find the best products for our GMCs. We always look through all our racing,
industrial supply, marine, RV, etc catalogs when we are looking for upgrade parts for our GMC so that we
know all the options available.

Date: Fri, 22 Jan 1999 08:57:21 -0600
From: "Travis Martin" <>
Subject: Re: GMC: Replace the battery diode isolator

May I offer a suggestion?
The diode isolator would be the best of both worlds if configured correctly. Since I don't (yet) own a GMC, I
can't say how the original is done, but... Modern diodes can be had fairly cheaply that will handle all the current
that your alternator will supply. And the voltage drop across the diode is of no consequence at all if the voltage
regulator sense line is connected to the battery and not to the "upstream" side of the diode; it actually should be
anyway to compensate for the voltage drop in the wire, which can be significant at times. The sense line is the
light gauge red wire coming from the two-conductor plug on the Delco alternator. Quite often on automotive
applications this sense lead is just connected directly to the alternator output stud a couple of inches away. In
this manner, the alternator output is regulated but the voltage at the battery is ASSUMED to be the same; not so
if there is a diode in the line.

If the sense line were instead connected to the battery positive terminal or at least on the battery side of the
diode, the voltage drop of the diode isolator would be a non-issue. And you don't have the reliability and coil
current issues of a relay or contactor.

As they say, just my .02
Travis...soon to be GMC'er

Date: Fri, 22 Jan 1999 14:13:18 EST
From: duane m simmons <>
Subject: Re: GMC: GMC Motorhome Digest V2 #209
Adding to Zak & Travis comments, which I agree with, is the following. The Diode Voltage Drop (approx. 0.8
v) is of no concern in charging batteries because the Vltage Sense Line to the Alternator is connected to the
output of the Isolator & is therefore compensated for in the Alternator's output voltage. It would be crime, in
my mind, to revert bach to an unreliable Electro Mechanical device in lieu of the solid state Isolator. Like going
back to vacuum tube TVs...low reliability & high cost.

Date: Fri, 22 Jan 1999 11:59:27 -0800
From: Henry Davis <>
Subject: Re: GMC: GMC isolator diodes

You are generally right about the isolator. However, there are conditions under which the 0.8 volt drop is
important. For one, the isolator dissipates heat proportional to the current flow. At full alternator current flow
the isolator diodes dissipate at most 80 watts or about 5 amps. For most MH uses you are right that the loss is a
"don't care." But, for those folks who rely on the alternator's full capacity, the lowered loss through a relay is

Most automotive type regulators do not provide the multistage high current charge profile of smart chargers.
Conversely, many marine applications include the smart regulator so that the engine can be used to recharge the
batteries in significantly less time.

My view on the GMC isolator is that the diode circuit is preferred unless you replace the regulator with a smart
multi-stage regulator - in which case you can really use all of the available current.

Date: Sat, 23 Jan 1999 11:49:22, -0500
Subject: Re: GMC: Replace the battery diode isolator

Great comments from some of my favorite folks. I did some research before jumping into this abyss. Here are
my references:

                                                                                                                   65 (pathmaker)
West Marine application note

I like the features and the easy install of the Combiner. Reliability is the issue so I will report back. Stay tunned
to this channel.


SOLENOID IS AN ELECTO-MECHANICAL DEVICE This was my strongest concern.
There are industry applications that still use these devices over solid-state devices( brakers over fuses, GFI
protectors,) The applications are usually high voltage, high current, and high overload situations. The boating
folks use switches and relays for reliability since it is real hard to get a jump in the middle of the ocean when
you suffer component failures. I have had to replace every diode isolator I have ever owned ( three different
rigs) and my GMC has had three isolators installed that I can indentify. So I am going to risk trying this

THE SOLENOID DRAWS POWER . The solenoid ONLY draws power when the chargers are in operation.
The 0.1 amp is about 0.1% of the alternator output. There is one combiner that uses a bi-stable solenoid that
requires no power in either position (ref #2). This power drain is not a problem and some of the units are made
to allow 600 amp overloads..

COMBINERS COST MORE. Yep, about two times the cost of an isolator. But I was going to buy an isolator
that was two times larger hoping it would last. So would have cost about the same.

DIODE DROP IS NOT IMPORTANT--- As Duane points out, the GMC is normally wired so that the
alternator compensates for the voltage drop of the diode to the engine battery. This does not adjust for the
voltage of the coach battery which should be the same unless you are running your 1000 watt inverter (or refer,
etc) and dropping more voltage across the
coach-diode in the isolator.

1) The combiner will allow the smart house charger to also charge the engine battery in the smart fashion
without adding any new wires. My engine battery now gets bulk, soak and float charging on shore power. You
have to wire around the diode isolator to use the smart multi-bank house charger. ( see the wiring diagram on
the web page)

2) The failure mode of a relay is normally open unless you ARC the contacts closed. This open circuit will
leave your batteries isolated and connected to their own chargers. The diode isolators failure mode is shorted
diodes which will connect the batteries together and allow them to discharge together. This is what left me

3) There is no heat generated in the combiner so little power is wasted and no heatsink is required. There are
internal overload sensors which protect the combiner. With the diode isolators the heat generated and high
transient loads might be causing the failures.

4) My dash battery voltmeter now tells me the voltage of the House battery, since they are connected together
during driving.

5) I get all of these features without any rewiring. Smart alternators and multi-bank house chargers require
rewiring adding current sensors, etc. The really good smart chargers use temperature compensation and do a
better job of charging. I just did not want to go that far.

- -------- REPLY, Original message follows --------

Date: Saturday, 23-Jan-99 09:30 AM

From: Philip L. Stewart       \ Internet: (
To: gmclist             \ Internet: (gmcmotorhome@mailinglists

Attachment: mimemsg.doc Code: 01S1N93 \ Created: Unknown [2 Kb]

Subject: Re: GMC: Replace the battery diode isolator

Zachary Zehnacker wrote:
> Phil,
> High amp solenoid relays were not that reliable for many years unless they were very expensive. I would
have to think that reliability and cost are probably among the major reasons that these battery combiners have
not been more popular in the RV industry..........


Thanks for your thoughtful and detailed reply to my question on battery isolators. It's just this sharing of
information, opinions, etc. that makes this forum so valuable to us GMC owners. Now I've got more insight
into the possible pros and cons of yet another upgrade option before spending the money and time on it.

Phil Stewart
'76 Transmode, TN

Date: Wed, 10 Feb 1999 02:34:33 EST
Subject: Re: GMC: Break downs / Alternator comments

In a message dated 2/9/99 9:10:19 PM MST, writes:

> An alternator failure has never seen me stranded, even without a spare. If it's daylight you can go a long ways,
>or at least far enough (usually) to get to a parts store and/or rest area/campground. You can go forever if your
>GenSet 12V is tied in ( and GenSet running ). It's not as many volts as the engine driven alternator puts out
>but enough to run everything including headlights.

   Good point. Actually, my stock buzz-box converter puts out around 40 amps when powered by the Onan,
enough to drive cross-country if you're judicious about power use. I carry a heavy (8 gauge X 12") jumper wire
which allows me to bypass the isolator diodes so the converter can charge the engine battery. (Came in handy
when my isolator failed a couple years ago. Allowed me to wait until I got home and could order a replacement
from J.C.Whitney.) As for the alternator itself, mine got a bit cranky last year when I added 12V element to
my refrigerator, wired direct to the alternator. Seems the additional 30 amps load, together with run-down
bateries, was too much, and it blew an output diode. Red light came on dimly, but a voltage check showed I
was still getting some output (although greatly reduced). So I drove it a few weeks until I could pull and
overhaul the alternator. A local rebuilder sold me a heavy-duty diode pack, and alll is well now. Strongly
recommend carrying some kind of voltmeter, so you can find out what's going on in case of alternator/battery
   BTW, this is another factor in favor of staying with mechanical fuel pump and belt-driven cooling fan. In an
emergency, if you turn everything else off (and pull the blower fan and compressor fuses), a fully-charged
battery could power the ignition system unaided and uncharged for many hundreds of miles. Maybe a thousand
if you jumper in the house batteries. Nice to have that capability just in case.

Rick Staples
'75 Eleganza
Louisville, CO

Date: Sat, 13 Feb 1999 11:31:28 -0500
From: Zachary Zehnacker <>
Subject: GMC: Statpower TC40 Information

Just wanted to let everyone here know that we got and installed our TC40 yesterday. I have put some of my
thoughts about it on the website <>. I also scanned the manual for it and put that
on the site as well.
Frame Off Pics
Honda EV6010 Info
Statpower TC40 Info
Race Team Info
.Home Page>

Date: Sat, 13 Feb 1999 17:17:40 PST
From: "Frank Folkmann" <>

Subject: GMC: TrueCharge 40
Need help.

  I am installing my True Charge 40. The original wires are 4 gauge. Do they need to be this heavy? To wire the
engine battery to the 2nd DC+.terminal will I require to run a lead to the battery. If yes what gauge?

Date: Sat, 13 Feb 1999 21:04:36 EST
Subject: Re: GMC: TrueCharge 40 + Onan Vasectomy

Having NOT installed my Trusecharge yet, (but I have used it to charge some golf cart batts elsewhere)....I was
wondering about the wire sizes existing in our coaches, but here is what I think (sorry, Arch). The #4
conductors run a short distance from the converter (or the charger which we are installing in it's place) to the
fuse block. The other cable runs to ground at the chassis.

We are capable of feeding the entire 12 volt house load at the fuse block, PLUS send 40 amps down the pike to
the coach battery via a #10 conductor.

According to my charts, a #10 will carry 30 amps a total of 10' total run, (there and back DC circuit), and that is
with a 3% voltage drop. I guess I am more concerned that the wire from the fuse block to the battery should be
replaced with a #8, which will carry 40 amps 10' total. It is the recharging capability that we all desire here, and
what is the point if the wire to the batts isn't big enough to haul the freight? Am I wrong here? I am glad this
was brought up, since I have not installed mine, but have been concerned with the weinie wire to the batteries.

I was not paying attention in class the day the teacher told us how to disable the small charger inherent within
the Onan. Need to do it. This is essential to the operation of any "smart" charger like the Statpower. Won't make
a diff when on shore power, but I am a boondocker. Can someone enlighten me on this operation? Thanks,
Larry Nelson, Springfield, MO PB 75

Date: Sat, 13 Feb 1999 21:18:35 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: TrueCharge 40

        Pages 17 and 18 of the TC40 manual give Statpower's recommendations for the wire gauge depending
on the wire length.
feet AWG
10    8
15    6
20    6
25    4
30    4
35->50 2

55->60 0
Unfortunately, the TC40 seems like it will accept 8 gauge max. They say to cut off enough strands of any
larger wire so that it will fit in the connector. I had to do that to get the 6 gauge that our original converter
used to fit.

Hope this helps,

Date: Sat, 13 Feb 1999 21:33:49 EST
Subject: Re: GMC: TrueCharge 40 + Onan Vasectomy
Please believe me when I say I am not being picky because you mangled my quote.<g> You have a total of 40
amps available to you. You have to subtract the house load from the 40 amps and that is what you will be
sending down the pike to the batteries. I am with you I dont like warm wires. Go a little bigger. The load
rates you quote are under perfect conditions. They wont exist in five years. Someone jump in here but since
mine did not come with a converter I have not studied them much. Most only charge about 3 or 4 amps. Thats
what the charging wire was designed for. I have not run the numbers yet because I am not there yet.
Off the top of my head I would not go less than #4 and I bet after I run the numbers and add in my own personal
pucker factor I will be a lot closer to #2 wire. Now thats what I think.
Take Care

Date: Sat, 13 Feb 1999 19:12:38 PST
From: "Frank Folkmann" <>
Subject: Re: GMC: TrueCharge 40
Mine has #4. It looks as some one had replaced the wiring. Inside the convertor the wire had been spliced and
taped. What size for the lead to the front? If we use the chart is it a #2. If so will not fit in connector...........Frank

Date: Sat, 13 Feb 1999 22:40:47 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: TrueCharge 40
We didn't run a wire up to the front. We might put one in later on, but we have never really needed it before.
Nothing runs off our start battery when parked, so it stays up. Now with a "smart" charger, we might be more
likely to add the extra wire.

From what the statpower manual says, "Strip 7/16 inch (instead of the 5/16 inch they normally want) insulation
from these wires and remove only enough strands of the conductor (wire) so that it fits into the charger
terminals." I did this to get our wire (also spliced and taped inside the old convertor like yours) to fit in the
Statpower terminal. I just started cutting off strands of the wire one by one until I could get what was left
to fit in the connector. I guess their feeling is that the wire will only be small diameter for the 1/2" that it is in

the connector. After that, the wire has the large gauge capacity needed for the long run. I would have preferred
a larger connector on the Statpower unit itself, but that probably would have made the unit more bulky and
expensive I guess. I might look into some kind of right angle adapter to attach the wires to and then attach that
to the statpower connectors. It was a tight fit to mount it vertically as they suggest, so the wires come out the
bottom and have to make a 90 degree turn almost as soon as they get out of the statpower connectors. It seems
ok though.

Date: Sat, 13 Feb 1999 22:47:54 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: TrueCharge 40

Get a solder on, solid copper connector for the wire that reduces to a size that will fit the connector. Thats what
I am going to do, have a thousand other things that come first however.

Date: Sat, 13 Feb 1999 21:20:18 -0700
From: "Richard Guthart" <>
Subject: Re: GMC: TrueCharge 40 + Onan Vasectomy
I had to perform this operation and I'm pleased to report that the patient survived the scalpel. Just disconnect the
wires from all terminals on the Onan's regulator and tape them off.*

As I recall there were 3 wires. Two of them went to the same pigtail so I left them joined together after pulling
them from the regulator.

This was the advice I received from contributors to this list and it was right on the mark.

I might add that if you ever have the flywheel off and want to make the operation irreversible, just remove the
stator. It's just dead weight now that you have disconnected it from the regulator.

*(The regulator is the solid state device with cast finned housing, and is shown on page 28-52 of the GMC Parts

Date: Sun, 14 Feb 1999 02:57:28 PST
From: "Frank Folkmann" <>
Subject: Re: GMC: TrueCharge 40

 The right angle connector sounds like a good idea. Will check that our after church this morning.

Date: Sun, 14 Feb 1999 17:15:05 EST
From: duane m simmons <>
Subject: Re: GMC: GMC Motorhome Digest V2 #255

Larry Nelson
While installing your TrueCharger 40+, it's not the current carrying capacity of the wire that is of concern, it's
the amount of voltage drop (resistance) under full charge that is of concern. The voltage drop is a function of
current & resistance (Voltage Drop = current x resistance). The voltage drop adversely effects the amount of
charge that is supplied to the battery. Best to use the #4 gauge wire for short runs (less than 5 ft) & # 2 gauge or
larger for the longer runs to optimize charger performance. This is applicable to the negative (ground/return) as
well. For the return wire, attach it to the battery cable at the chassis tie point. as well as the existing tie point.
To eliminate the Onan Voltage Regulator (Onan Power problem), remove the wires attached to the Onan
Voltage Regulator (VR) & tape them up while maintaining the connection of wires attached to each other at the
VR. Typically there is one pair of wires attached to the same terminal at the VR that must be maintained
attached to each other. A side benefit of removing these wires from the VR is that when the VR fails, it loads
down the input AC voltage that can be a problem with the interface at the ONAN Control Board. Terminal 8 to
11 should be 26 to 30 volts AC while the Onan is running. A faulty VR can load down this signal to less than
20 volts AC. BTW this VR is not needed for operation when the Onan shares a Battery for house power, only
when the Onan has a dedicated battery for the Onan power. Most, if not all coaches have been built at the
factory with a common House & Onan battery or they have had a field retrofit (early 73 & 74 Coaches).
Harry GMCing

Date: Sun, 14 Feb 1999 18:13:52 -0500 (EST)
From: "Thomas G. Warner" <>
Subject: Re: GMC: Power Switch

Why not Zak? He could duplicate our circuitry and eliminate the transfer switch. Replace it with the receptacle
and plug like we have. than he could install the statpower 40.

Date: Sun, 14 Feb 1999 19:12:38 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: Power Switch


I didn't mean to imply that the TC40 wouldn't benefit him as much as I expect it to benefit us. I just felt that the
TC40 is a separate upgrade which I felt had nothing to do with the problem he asked. He seemed to ask if the
TC40 would act like a transfer switch. It will not. For his problem (at least the way I understood it anyway),
his 120V AC -> 12V DC device (ie OEM converter or TC40) is irrelevant.

You are correct that he could duplicate our wiring to solve his problem, but I think an automatic transfer switch
would probably be the better way to go. I don't think it would be any harder to install. It could even be easier

to install depending on where the generator wires are located. With the transfer switch, he wouldn't have to
unplug/plug in the generator every time he wanted to switch between shore power and generator power like we
do. He would simply plug in the shore power and it would work. When he started his generator, the transfer
switch would wait until the generator was supplying good voltage (ie after it has started to run a little) before
switching over to the generator power. It would also shut down the power before the generator voltage dropped
too much. This keeps things from trying to run off the low voltage that the generator provides when it is
starting/stopping. This, IMO, is a better situation than what we have and is an upgrade in itself.

Just my opinions,

Date: Sun, 14 Feb 1999 16:56:21 -0800
From: "Heinz Wittenbecher" <>
Subject: Re: GMC: Power Switch / TS30 relay


I got a TS-30 and TS-50 from Jim Bounds last year. I actually only used the time delay module as my
Transmode has a switch-over relay similar to what's used in the TS's already installed. ( The rest is now 'spare

The TS-50 is large physically. Unless you have 2 AC's I would guess that you'd never draw 50 amps when
running on the GenSet.

The TS-30 may be ample for normal needs and is much easier to install.

The scheme of it is that by default, i.e. relay de-energized, the contacts are closed to shore power. When GenSet
is started the output is sensed by the time delay and after a short time the relay is energized and coach switches
to GenSet power. The time delay is sufficient for the GenSet to be stable before relay is energized.

It would be a simple retrofit as it's all in it's own enclosure. If you need some measurements on the enclose, let
me know.

Date: Sun, 14 Feb 1999 20:33:28 -0500
From: Zachary Zehnacker <>
Subject: Re: GMC: Power Switch / TS30 relay


The capacity might not be as important as how it handles the circuits. The GMC wiring is set up so that it gets
two feeds from the 6K Onan. It gets one 30 amp feed and one 20 amp feed. The 20 amp feed is mostly for the
A/C and some small appliances, while the 30 amp feed is mostly for everything else. These circuits are kept

totally separate. Even though our 23' came with the 4K Onan which only provided the 30 amp service, it was
still wired for the separate circuits which made installing the 6K Honda much nicer.

I believe that the 50 amp transfer switch would keep them separate, but the 30 amp one would combine them. I
suspect this is why the 50 amp one is so much bigger. Do you know if this is true? I don't know if it would be
good to combine the two outputs of the Onan or not. I suspect, serious problems could arise if you
inadvertently got close to the 50 amp draw with it set up like this. It might be easier to exceed 30 amps than
you think. With the A/C and Microwave on we would trip our 20 amp breaker. If you add the converter's 7 amp
draw or so, we were definitely higher than 30 amps total. We have now moved everything over to the 30 amp
service except for the A/C and have not had any further problems.

As a side note, one of the adapters used only when plugging it into shore power does combine the two circuits
together so they both get power when hooked to a normal 15-20 amp outlet. In this case, however, the shore
power's breaker is expected to limit the current to acceptable levels.


Date: Sun, 14 Feb 1999 20:38:28 -0500
From: Richard Waters <>
Subject: Re: GMC: Power Switch / TS30 relay

Thanks for the info.

I see that Campers Choice has 2 generator switches. A 30 AMP ($49.95) and a 50 AMP ($84.95). Are those
the same units? I only have 1 AC unit, however our power at home has been going out a lot lately. I utilized
the generator of the coach to run the house a few times this Winter, but was limited to 2 20 AMP circuits. I
thought that if I had all 50 AMPS available to my house, I would be better off. That's another design for me to
ponder, but that would cause me to consider the 50 AMP unit.

Richard Waters
'76 Palm Beach

Date: Sun, 14 Feb 1999 23:13:16 EST
Subject: Re: GMC: Power Switch

  I've flogged this issue to death in <rec.outdoors.rv-travel> , with my copy of the National Electric Code in
hand. But let me try once again: There are apparentlty some SOBs that were wired for "50 amp" shore power
as an afterthought. These half-baked, cobbled-up coaches DO put most of the coach on one 30-amp/120 volt
breaker, and the second AC unit all by itself on a separate 20-amp/120V circuit. They can draw a MAXIMUM
of approx. 6,000 watts total from shore power or generator. (20 X 120 = 2400) + (30 X 120 = 3600) = 6,000.

  OTOH, a proper 50-amp campground hookup (according to code!) can supply 2 separate 50-amp circuits.
These may either be (2) 120V/50A circuits (as our GMCs were set up), or (1) 240V/50A 3-wire circuit (4 wires
incl. ground). In either case, the hookup works out to 12,000 watts. (Doesn't matter whether the campground
hookup is 2 X 120V or 1 X 240V, we can safely plug into it.) But wait, it's even more dramatic than that.
According to the NEC, a 30 + 20 campground hookup is considered to be either 20 OR 30 amps, and so is
nominally required to supply ~ 3,600 watts total, whereas a 50 amp hookup is required to supply a nominal
9,600 watts. All this is further complicated by various de-rating calculations, but the bottom line is that a 50-
amp hookup delivers MORE than twice as much power than a 30 + 20.

  Our GMCs are an early offshoot of the 50-amp service, with a pair of 40-amp breakers as the main
disconnect. They still will draw up to the nominal 9,600 watts of the hookup on shore power. For lots of gory
details, I'm referring to Article 551, "Recreational Vehicles, Parks" of the 1993 National Electrical Code.

  My main point is to discourage anyone from buying or installing a 30 + 20 amp entrance or transfer, which
would be a real downgrade of our "ahead of their time" GMCs. More and more RV parks are providing 50-amp
hookups, so it's nice to be able to use them.

My .02.
Rick Staples
'75 Eleganza
Louisville, CO

Date: Mon, 15 Feb 1999 11:16:57 -0700
From: D & D Lowry <>
Subject: GMC: Power Switch

Well, I recently installed a Statpower 40 in my '76 Royale and its not working. Mine is wired so that we need to
manually flip a breaker when changing from the Onan to shore power, and the Statpower was wired in exactly
the way the old "hummer" was. When it was first installed, it's fan came on and the lights indicated it was
charging. But when we checked a week later, the house batteries were dead and there was no 12V power,
despite being plugged into shore power. (the AC receptacles were hot.)

Were taking the ol' boy up to the bay area this Friday, so I made an appointment for tomorrow (Tues.) a.m. to
have the $65/hr tech look at it. But first, I thought I'd check here to see if my problem might be something
"simple" (thus saving the bucks for other needed upgrades).

If any of you "experts" have any suggestions, please e-mail me directly so that I can act on them quickly (I
might not get "digest" comments in time).

When we get back, I'll be looking to install a power switch to eliminate the need to switch between Onan and
shore power.
Dave (& Dege), Santa Barbara, '76 Royale 26'

Date: Mon, 15 Feb 1999 15:09:15 -0500
From: Ritch Hwang <>
Subject: GMC: Power Switch / TS30 relay


Todd Engineering web site:

Date: Mon, 15 Feb 1999 13:07:59 -0700
From: "Richard Guthart" <>
Subject: Re: GMC: Power Switch

By any chance is your Statpower's AC cord plugged into the circuit protected by a GFI circuit breaker?

Mine was, and it would frequently trip the breaker. I wired a duplex receptacle into one of the other circuits for
it, and now it works just fine.

I think I saw something on Statpower's web site about using their smart chargers on GFI-protected circuits.

Hope this helps.

Date: Mon, 15 Feb 1999 20:52:31 -0600
From: "Travis Martin" <>
Subject: GMC: Fw: WTS 4KVA Sine wave inverter.

- -----Original Message-----
Date: Monday, February 15, 1999 6:27 AM
Subject: WTS 4KVA Sine wave inverter.

>Have an unused 4KVA Sine wave inverter. This inverter takes 48VDC input (from your battery bank) and
>provided 115VAC (60Hz) at 34Amps, continous, sine wave, output. Output is very clean as these are
>designed to be used as backup for telephone equipment and as power for instrumentation such as oilfield
>wireline stuff.
>Made by Abacus Controls in NJ.
Sell $1500.00 (over $6000 if you want to buy from manufacturer)
>Includes automatic change over relay for use as backup power source.


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