Voltage Drop Charging System

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Voltage Drop Charging System Powered By Docstoc
					    Charging System tests
    & Voltage information

Checking the charging system with just a volt meter
                  First Step
Always check the battery first.   A bad battery can
affect the charging test.

Battery Voltage should be 12.6 volts when car is
off. If not we need to find out Why? If over it is
probably because the car has been running and
was just shut off. If under it is bad or not being
charged. Battery state of Charge if below 12.45
charge before testing.

Charging system must supply enough energy to
run the demands of the car and charge the
Turn off everything run at 2000-2500
for 2 minutes and check charging
system voltage. The results should
be some where around the following

Sealed Maintenance free battery
above 15.5V overcharging
14.5V -15.4V normal
13.2V - 14.4V may be to low
12.6V - 13.1V too low
12.6V or less not charging
Low Maintenance battery
above 14.8V overcharging
13.2V - 14.7V normal
12.6V - 13.1V too low
12.6V or less not charging

                      New cars at 80 degrees
                      Ford 14.4V- 14.8V
                      Gm 14.5V - 15.1V
                      Chrysler 13.3V - 13.9V
            Generic Quick Specs

   Battery Voltage should be 12.6 volts when car
    is off.
   Voltage should be with car running at 2000
    RPM about 13.8-14.8 Volts
   Voltage should never fall below 13.2 Volts
         Things to Remember

   Temperature changes charging voltage
   Higher in cold weather

   Age of battery changes charging voltage
   Older batteries have less charge
    acceptance, will elevate voltage faster
         Things to Remember

   State of charge, changes charging
   Low battery voltage, charging voltage
    will be lower

   Impurities, If you have added tap water
    charging voltage will be lower
          Check for Overcharge

   1. Engine off - Write down voltage of
   2. Turn all accessories off
   3. Run at idle - Write down voltage
   4. Run up to 2000 RPM - Write down
   Voltage should not go up 2.5 volts over
    battery voltage from step # 1
           Check for undercharge

   1. Engine off - Write down voltage of
   2. Run for 2 minutes at 2000 RPM
   3. Turn on all accessories
   4. Take voltage reading, Should go up
    at least .5 volts Minimum voltage is 13.2
    But if charging system is working right
    you should see between 13.7-14.4
                Tech Tips
If voltage does not go up full field the
Charging system. Put battery voltage
into the coil windings to check the
Alternator. (Cannot be done on some
cars with internal voltage Regulators
or cars that the regulation is
controlled by the computer.)

If diode trio burns out on GM
products idiot light will be on but it
will still charge. (might be dim)
               Voltage drop

   You always want to perform a voltage drop
    test when checking out a charging
    problem. Also can be called a circuit
    resistance test.
   You need to check the ground side and the
    insulated side vehicle must be running and
    a load must be applied. You can add a
    load by just turning on the lights, heater
    and other accessories.
           Voltage drop Insulated

   Hook up Positive
    lead to the output of
    the alternator

   Hook up Negative
    lead to the Positive
    terminal of the
           Voltage drop Insulated

   The reading should be less then .5 Volts This
    one is at .154 volts.

    should be
    in the DC
    volt scale
       Voltage drop ground side

   Hook up Positive
    lead to the
    Negative side of
    the battery.

   Hook up the
    negative lead to
    the frame of the
       Voltage drop ground side

   The reading should be less then .2 Volts
    This one is at .036 volts.
          The End for Now

Get into the habit of checking the
charging voltage on every car that comes
into the shop. Not just when you have a
problem. Then when a car comes into
your shop you should know what the
voltage is or should be before you even
hook up a meter.
Check for Understanding:
1.   What is another name for a voltage drop
2.   As a rule, what should the voltage be on
     a low maintenance battery that is
     running at 2000 rpm?
3.   Write out how you can check for
     maximum alternator output using a
4.   What must you do to accurately check
     the ground side?
5.   A properly functioning charging system
     should show a range of how many volts?