Generator Type power sources convert mechanical energy or mechanical power that is obtained from an inter-
nal combustion engine into electrical power suitable for arc welding and/or auxiliary electrical power. For
welding, two basic types of rotating power sources are used, the generator and the alternator. Both designs
have a rotating member, called a rotor. A system of magnetic field excitation is needed for both types.
There are three essentials for electrical power generation:
       1. Magnetic Lines of Force (Magnetic Field)
       2. Electrical Current Carrying Conductor
       3. Relative Motion Between the Magnetic Field and the Electrical Current Carrying Conductor.
In electrical power generation, there must be relative motion between a magnetic field and a current carrying
conductor. Whenever a wire moves through the lines of force of a magnetic field or whenever lines of force of
a magnetic field are moved through a wire, a voltage is induced in the wire. This induced voltage causes elec-
tric current to flow when the circuit is complete. Thus, the principle of any rotating power source is that elec-
trical current is produced in electrical conductors (coil of wire) when they are moved through a magnetic field.
Physically, it makes no difference whether the magnetic field moves or the conductor moves, just so that the
coil experiences a changing magnetic field intensity.

                                                    Page 1
The amount of voltage generated depends upon the number lines of force cut per second. Three ways of
increasing the voltage from a generator are (1) by increasing the motion (speed/velocity)of the magnetic field
(or the coil), (2) by using a stronger magnet (or magnetic field), and (3) by increasing the number of turns of
wire in the coil.
A direct current generator consists of a rotor and a stator. The stator or the stationary portion of the generator,
within which the rotor assembly turns, holds the electromagnetic field coils which conduct a small amount of
direct current to maintain the necessary continuous electromagnetic field excitation required for power genera-
tion. Direct current is used to create the electromagnetic field. The direct current for the field windings of the
generator is called the exciting current, and the generator that supplies the direct current is called the exciter.
This direct current amperage is normally no more than 10 to 15 ampere and very often is less. Electromagnets
provide stronger magnetic fields and control the amount of induced current. This control is important, for
when the amount of current flowing through the electromagnets is changed, the strength of the magnetic field
is changed.
The rotor assembly consists of (1) a through shaft, (2) two end bearings to support the rotor and shaft load, (3)
an armature which includes the laminated armature iron core and the current-carrying armature coils. It is in
the armature coils that the electrical welding power is generated. And (4) a commutator brush arrangement for
mechanically rectifying or changing alternating current to direct current welding power.

In actual practice, the armature turns within the stator and its electromagnetic field system, and welding cur-
rent is generated. The AC voltage produced by the armature coils moving through the magnetic field of the
stator is carried to the copper commutator bars through electrical conductors from the armature coils. The
commutator is located at one end of the armature. The commutator is a system of copper bars mounted on the
rotor shaft. The conductors are soft-soldered to individual commutator bars. The latter may be considered as
terminals, or "collector bars," for the alternating current generated from the armature. It is a group of conduct-
ing bars arranged parallel to the rotating shaft to make switching contact with a set of stationary carbon brush-
es (contact points). These bars are connected to the armature conductors. The whole arrangement is construct-
ed in proper synchronization with the magnetic field. As the armature rotates, the commutator performs the
function of mechanical rectification.
Each copper bar has a machined and polished top surface. Carbon contact brushes ride on that top surface to
pick up each half-cycle of the generated alternating current. The carbon contact brushes pick up each half-
                                                     Page 2
cycle of generated alternating current and direct it into a conductor as direct current. The purpose of the com
mutator is to carry both half-cycles of the generated AC sine wave, but on separate copper commutator bars.
Each of the copper commutator bars is insulated from all the other copper bars.

                                                                                                    2 POLE
                  VOLTAGE AT BRUSHES                                                              GENERATOR

                                                                            N          AC          S
           TIME                                                                       HERE
              INDUCED                                 (+)

                                                    DC HERE


         The magnetic field is contained in the stator assembly of a generator. It is in the armature coils
           that welding power is generated. The commutator-brush rectifies ac to dc welding power.

                                                  DC Generator
Normally, the direct current generator is a three-phase electrical device. Three-phase welding systems normal-
ly provide the smoothest welding power of any of the electromechanical welding power sources.

               1. END VIEW OF THE ARMATURE AND                     2. END VIEW OF FOUR POLE ROTOR
                   FIELD COILS OF GENERATOR                           AND STATOR OF ALTERNATOR

                                                      Page 3
The entire line, of Miller Electric's engine driven power sources, uses a design concept called the "revolving
(electromagnetic) field design." This concept is commonly called an alternator design (often called an alternat-
ing current generator). This design in welding power sources is in direct contrast to how DC generator rotating
power sources are designed. There are distinct differences and advantages to using alternator design over the
DC generator design. It is very similar, except the alternator rotor assembly contains the electromagnetic field
coils instead of the stator coils as found in generators. The heavy current-carrying conductor windings are
wound into the stator. These machines are also called revolving or rotating field machines.
Slip rings are used to conduct low DC power into the rotating member to produce a rotating electromagnetic
field. An alternator usually has brushes and slip rings to provide the low direct current power to the field coils.
It is not usual practice in alternators to feed back part of the welding current to the field circuit. Rather the
alternator usually uses the brushes and slip rings to provide the low DC power to the field coils. The voltage
induced in the armature coil passes through a set of slip rings connected to the ends of the armature coil and
through a set of brushes making contact with the slip rings, to an external circuit. This configuration precludes
the necessity of the commutator and the brushes used with DC output generators.
The welding output is alternating current, which requires external rectification for direct current applications.
Rectification is usually done with a bridge rectifier using silicon diodes. Both single and three-phase alterna-
tors are available to supply AC to the necessary rectifier system. The DC welding characteristics are similar to
those of single and three-phase transformer-rectifier units.

                                                     Page 4
The alternator design presents several fundamental advantages. Some important facts are:
Miller Alternator Design                                Generator Design

1. Higher duty cycle - 100%                                  Lower duty cycle - 60%
   - Design permits 100% duty cycle rating.                  - To obtain higher duty cycle requires heavier
                                                               windings in the armature.
                                                             - Small units are usually 30-50% duty cycle rated.

2. Operates cooler                                           Harder to cool
   - Most heat is generated in the weld windings.            - Heat is generated in the armature. Must be cooled
     located on the outside of the unit.                       by air movement and conduction to the outside of
   - Easy to cool.                                             the unit.
   - Minimum cold to hot drift.                              - More heat build up, greater cold to hot drift. Output
                                                               will drop off when unit heats up.

3. Low currents in moving parts                              High current in moving parts
   - Rotating field coils carry less than 10 amps.           - Armature carries full welding current. Heat builds
                                                               up internally.

4. No brush-commutator assembly                              Brush assembly and commutator bars
   - Slip rings and brush carry less than 10 amps.           - Brushes must carry full welding current.
   - Minimum brush wear.                                     - Arcing occurs.
   - No chance of polarity changing.                         - Brushes wear, lowering efficiency, maintenance
                                                             - Welding polarity may change during welding when
                                                               brushes lift off the commutator.
                                                             - Commutator will require maintenance.

5. Rotor is lighter                                          Armature is a large mass of iron
   - Quicker to accelerate to speed.                         - Slower to respond.
   - Rotates easier, engine easily handles 300 amp           - Engine can only handle a 200 amp power source.
     power source.                                           - More torque required to rotate. Harder on bearings,
   - Less fuel consumption for same amperage                   etc.
     output.                                                 - During heavy usage such as arc gouging, stress
                                                               relieving, etc. heat buildup will cause solder to be
                                                               thrown from commutator area.

6. No "kits" required for paralleling                        Special kits required to parallel
   - Hook any number of units together for increased         - Adapter kits required to connect units together.
     output.                                                   Current feedback from one unit to another causes
   - No current feedback can occur since diodes                one to "drive" the other as a motor.
     block feedback.

                                                     ROTOR COMPARISONS

                   ROTATING MAGNETIC
                    FIELD COIL DESIGN
                   OF AN ALTERNATOR
                    100% DUTY CYCLE
                                                                           ROTATING ARMATURE
                                                                               DESIGN OF A
                                                                             60% DUTY CYCLE

                                                       Page 5
The blocking nature of the rectifiers makes direct current alternator units easy to operate in parallel for obtain-
ing increased welding current output by connecting two or more welding alternators (generators) in parallel.
Care should be taken to ensure that connections are the same polarity. All units paralleled must be set to deliv-
er equal welding (amperage & polarity) outputs. Parallel connection is not advised unless the manufacturer's
specific instructions are followed. Such a precaution is necessary because successful paralleling depends upon
matching the output-voltage, output amperage setting, and polarity of each machine.
In the case of self-excited generators, the problem may be further complicated by the necessity to equalize the
excitation between the generators.
Both the generator and alternator type power sources generally provide welding current adjustment in broad
steps called ranges. A rheostat or other control is usually placed in the electromagnetic field circuit to adjust
the internal magnetic field strength for fine adjustment of power output. The fine adjustment of welding power
output regulates the strength of the magnetic field, and will also change the open circuit voltage. When the
rheostat is adjusted near the bottom of the range with a low rheostat setting, the open circuit voltage will nor-
mally be substantially lower than at the high end of the range.

                                   Typical Engine Drive Amperage Control
With many alternator power supplies, broad ranges are obtained from taps on a reactor in the AC portion of
the circuit. As such, the basic machine does not often have the dynamic response required for shielded metal
arc welding. Thus, a suitable inductor is generally inserted in series connection in one leg of the DC output
from the rectifier. Welding generators do not normally require an inductor.
There is a limited range of overlap normally associated with rotating equipment where the desired welding
current can be obtained over a range of open circuit voltages. If welding is done in this area, welders have the
capability to fine tune or adjust the arc to the job. With a lower open circuit voltage, the slope of the voltam-
pere curve is less. This allows the welder to regulate the welding current to some degree by varying the arc
length. This can assist in weld-pool control, particularly for out-of-position welding.
A generator or an alternator unit produces a maximum or a finite amount of power that is measured in kilo-
watts. As the voltage increases the amperage will decrease proportionately. Conversely as the voltage decreas-
es the amperage will increase proportionately. In other words, if there is a relatively high open circuit voltage
at some particular setting on a power source, there must be a relatively limited amount of maximum short cir-
cuit current at the same time.

                                                     Page 6
                                                                                  The volt-ampere curves show the
                                                                                  minimum and maximum voltage
                                                                                  and amperage output capabilities of
                                                                                  the welding generator. Curves of all
                                                                                  other settings fall between the
                 100                                                              curves shown.
                 80                                              185–425
      DC VOLTS



                       0   100   200   300    400   500   600   700   800   900
                                             DC AMPERES

                                                      Volt-Amp Curves
Welding power sources are available that produce both constant current and constant voltage. These units are
used for field applications where both are needed at the job site when primary, utility power is not available.
Also, many new designs use electronic solid-state circuitry to obtain a variety of volt-ampere characteristics.
Saturable reactors and moving-core reactors may be used for output control of these machines. The normal
method is to provide a tapped reactor for broad control of current ranges, in combination with control of the
alternator magnetic field to produce fine control within these ranges.

MILLER welding generators are combination welding and power generators specifically designed for the
welding application. An auxiliary power winding is included in the generator to provide convenience power
incidental to the welding operation for accessory equipment. Most auxiliary power generators are singlephase
and may be either two-wire or three-wire design depending upon the model. There is no significant advantage
of the two-wire system versus the three-wire except that the three-wire design is capable of supplying two dif-
ferent voltages simultaneously (120/240 VAC).
These machines are designed to provide nominal 120 or 240 volts, 60 Hertz power, which are the common
small load voltages in the United States. Different voltages and frequencies are found in various parts of the
world and optional auxiliary power generator designs are available for these requirements. These generators
can be used to power portable tools, lights, heaters, compressors, pumps, etc., within the capabilities of the
unit. They are not designed to power voltage and/or frequency sensitive electronic equipment which may be
damaged by voltage or frequency changes normal to the operation.
An alternator or generator may be either self-excited or separately-excited, depending on the source of the
field power. Either unit may use a small auxiliary alternator or generator, with the rotor on the same shaft as
the main rotor, to provide exciting power. On many engine-driven units, a portion of exciter field power is
available to operate tools or lights necessary to the welding operation. In the case of a generator, this auxiliary
power is usually 115 volts of direct current. With alternator-type power source, 120 or 120/240 volts of alter-
nating current is usually available. Alternating Current Voltage frequency (hertz) depends upon the engine

                                                           Page 7
speed. The frequency of the output welding current is controlled by the rotation of the rotor assembly and by
the number of poles in the alternator design. A two-pole alternator must operate at 3600 rpm to produce
60 Hz alternating current, whereas a four-pole alternator design must operate at 1800 rpm to produce 60 Hz
alternating current.

                             N                         S

                                             AC HERE

                                           2 Pole Alternator With Tapped               STABILIZER
                                           Reactor For Coarse Current                  (INDUCTOR)
               FINE AMPERAGE               Control And Adjustable Magnetic
                ADJUSTMENT                                                      DC
                                           Field Amperage For Fine Current     HERE
                                           Output Control

      1. Two Pole Alternator
      2. Four Pole Alternator

                                                   Page 8
                                       Two Pole Alternator

                                       Four Pole Alternator

      1. Generator Sizing
      2. Load Analysis

Rated Output
Found on machine nameplate
E.G. Trailblazer 301:      9,500 Watts
                           120 Volts - 84 Amps
                           240 Volts - 42 Amps
                           kVA while welding is dependent on welding output

                                               Page 9
1. Generator Sizing: How Much Power Can Generator Supply?

                                           Limits of a Generator
MILLER welding generators are designed to operate at maximum load, but doing so allows very little reserve
engine horsepower to follow changes in load requirements. This makes itself known by noticeable voltage and
frequency changes (light bulbs flicker, etc.) Much improved voltage and frequency regulation can be realized
by not loading the generator to 100% of its capacity. For best performance and load handling, only use approx-
imately 90% of the available output. The 10% margin allows for more satisfactory engine governor response
to changing load situations. The rule becomes simple: Always know the total load requirements and the gener-
ator's capability. Select a generator to adequately meet load requirements, or limit load requirements to the
capabilities of the existing generator.
2. Load Analysis: How Much Power Does Equipment Require?

                                                  Page 10
Load analysis and generator sizing are essential for satisfactory generator and equipment operation. The avail-
able auxiliary power is limited by engine horsepower and is a small, finite power system as compared to the
large, seemingly-infinite electric utility system. Any single load may represent usage of a large portion of the
total power available. It is necessary to carefully determine the total load that will be applied by adding up all
the individual loads. Some tools are rated in watts, others in amperes. Lights and heaters are rated in watts.
Most equipment will specify on its nameplate what its specific requirements will be.
For example, a drill requires 4.5 amperes at 115 volts. Watts equals volts times amperes. Therefore, this drill
requires approximately 520 watts. Add three 200 watt flood lamps, and requirements increase by 600 watts for
a total of 1120 watts. Continue in this fashion until all loads have been added. Be sure to add all motor run-
ning requirements to the total (motor starting requirements will be discussed later). Consider also that a load is
not always constant. To be sure, lights and resistance heaters are constant, but portable power tools are not.
One rarely grinds or drills with a constant, even pressure. Thus, the load requirements change greater than
anticipated. Induction motors normally power loads that require variable amounts of power from the generator
and will be discussed later.

                                                    VOLTS x AMPERES = WATTS

         This equation provides an actual power requirement for resistive loads, or an approximate running requirement for non-
         resistive loads.

         EXAMPLE 1: If a drill requires 4.5 amperes at 115 volts, calculate its running power requirement in watts.

                                                             115 V x 4.5 A = 520 W
                                         Therefore, the individual load applied by the drill is 520 watts.

         EXAMPLE 2: If a flood lamp is rated at 200 watts, the individual load applied by the lamp is 200 watts. If three 200 watt flood
         lamps are used with the drill from Example 1, add the individual loads to calculate total load.

                                                (200 W + 200 W + 200 W) + 520 W = 1120 W

                                Therefore, the total load applied by the three flood lamps and drill is 1120 watts.

                                     Calculating Power Required To Run Equipment

                                                                   Page 11
Starting Motors
Different types of loads require different types of output from the generator. When a nonmotor load is applied,
generator output goes to the ampere requirement of the equipment, but voltage remains near rated. The non-
motor load does not cause the voltage to drop significantly below its nominal rating. When a motor load is
applied, the generator will attempt to supply motor starting current causing output voltage to drop to nearly
zero volts because the starting current is many times the running current. For this reason, it is necessary to
determine the starting amperage required by the motor and verify the the generator can supply that amount of
amperage. This can be done using the formula shown below, or by using the charts shown on the following

                                     4                                                           1   Motor Start Code
                                                      AC MOTOR                        2          2   Running Amperage
                                     1          VOLTS 230   AMPS 2.5
                                                                                                 3   Motor HP
                                     3          CODE M      Hz    60
                                                                                                 4   Motor Voltage
                                                HP    1/4   PHASE 1
                                                                                                 To find starting amperage:
                                                                                                 Step 1: Find code and use table to
                                                                                                 find kVA/HP. If code is not listed,
                                                                                                 multiply running amperage by six to
                                                                                                 find starting amperage.
                                                                                                 Step 2: Find Motor HP and Volts.
                                                                                                 Step 3: Determine starting amper-
                                                                                                 age (see example).
                                                                                                 Welding generator amperage out-
                                                                                                 put must be at least twice the
                      Single-Phase Induction Motor Starting Requirements                         motor’s running amperage.

            Motor Start
              Code            G         H        J       K       L      M       N          P

             KVA/HP          6.3     7.1        8.0     9.0    10.0    11.2    12.5       14.0

                          kVA/HP x HP x 1000
                                                     = STARTING AMPERAGE
                EXAMPLE: Calculate the starting amperage required for a 230 V, 1/4
                HP motor with a motor start code of M.
               Volts = 230   HP = 1/4       Using Table, Code M results in kVA/HP = 11.2

              11.2 x 1/4 x 1000
                                = 12.2 A Starting the motor requires 12.2 amperes.
                     230                                                                                                      S-0624

                                         Caculating Motor Starting Requirements

                                                                Page 12
Approximate Power Requirements for Industrail Motors
                   Industrial Motors       Rating        Starting Watts   Running Watts
   Split Phase                             1/8 HP             800               300
                                           1/6 HP            1225               500
                                           1/4 HP            1600               600
                                           1/3 HP            2100               700
                                           1/2 HP            3175               875
   Capacitor Start-Induction Run           1/3 HP            2020               720
                                           1/2 HP            3075               975
                                           3/4 HP            4500             1400
                                            1 HP             6100             1600
                                          1-1/2 HP           8200             2200
                                            2 HP             10550            2850
                                            3 HP             15900            3900
                                            5 HP             23300            6800
   Capacitor Start-Capacitor Run          1-1/2 HP           8100             2000
                                            5 HP             23300            6000
                                          7-1/2 HP           35000            8000
                                           10 HP             46700            10700
   Fan Duty                                1/8 HP            1000               400
                                           1/6 HP            1400               550
                                           1/4 HP            1850               650
                                           1/3 HP            2400               800
                                           1/2 HP            3500              1100

Approximate Power Requirements for Farm/Home Equipment
                 Farm/Home Equipment      Rating         Starting Watts   Running Watts
   Stock Tank De-Icer                                        1000            1000
   Grain Cleaner                          1/4 HP             1650              650
   Portable Conveyor                      1/2 HP             3400            1000
   Grain Elevator                         3/4 HP             4400            1400
   Milk Cooler                                               2900             1100
   Milker (Vacuum Pump)                     2 HP             10500           2800
   FARM DUTY MOTORS                        1/3 HP            1720              720
   Std. (e.g. Conveyors,                   1/2 HP            2575              975
   Feed Augers, Air                        3/4 HP            4500            1400
   Compressors)                             1 HP             6100            1600
                                          1-1/2 HP           8200            2200
                                            2 HP             10550           2850
                                            3 HP             15900           3900
                                            5 HP             23300           6800
   High Torque (e.g. Barn                 1-1/2 HP           8100            2000
   Cleaners, Silo Unloaders,                5 HP             23300           6000
   Silo Hoists, Bunk Feeders)             7-1/2 HP           35000           8000
                                           10 HP             46700           10700
   3-1/2 cu. ft. Mixer                     1/2 HP            3300            1000
   High Pressure 1.8 Gal/Min              500 PSI            3150              950
   Washer 2 gal/min                       550 PSI            4500            1400
          2 gal/min                       700 PSI            6100            1600
   Refrigerator or Freezer                                   3100              800
   Shallow Well Pump                      1/3 HP             2150              750
                                          1/2 HP             3100            1000
   Sump Pump                              1/3 HP             2100              800
                                          1/2 HP             3200            1050

                                            Page 13
Approximate Power Requirements for Contractor equipment
                       Contractor         Rating          Starting Watts   Running Watts
  Hand Drill                                1/4 in              350             350
                                            3/8 in              400             400
                                            1/2 in              600             600
  Circular Saw                             6-1/2 in             500             500
                                           7-1/4 in             900             900
                                           8-1/4 in           1400             1400
  Table Saw                                  9 in             4500             1500
                                            10 in             6300             1800
  Band Saw                                  14 in             2500             1100
  Bench Grinder                              6 in             1720              720
                                             8 in             3900             1400
                                            10 in             5200             1600
  Air Compressor                           1/2 HP             3000             1000
                                            1 HP              6000             1500
                                          1-1/2 HP            8200             2200
                                            2 HP              10500            2800
  Electric Chain Saw                   1-1/2 HP, 12 in         1100            1100
                                         2 HP, 14 in           1100            1100
  Electric Trimmer                      Standard 9 in           350             350
                                      Heavy Duty 12 in          500             500
  Electric Cultivator                      1/3 HP             2100              700
  Elec. Hedge Trimmer                       18 in               400             400
  Flood Lights                               HID                125             100
                                        Metal Halide            313             250
                                          Mercury             1000
                                           Sodium             1400
                                            Vapor             1250             1000
  Submersible Pump                        400 gph               600            200
  Centrifugal Pump                        900 gph               900            500
  Floor Polisher                        3/4 HP, 16 in         4500             1400
                                         1 HP, 20 in          6100             1600
  High Pressure Washer                     1/2 HP             3150             950
                                           3/4 HP             4500             1400
                                            1 HP              6100             1600
  55 gal Drum Mixer                        1/4 HP             1900             700
  Wet & Dry Vac                            1.7 HP               900            900
                                          2-1/2 HP            1300             1300

                                             Page 14
Auxiliary Power While Welding

     Weld Current           Total Power            120 V Receptacle                240 V Receptacle
     in Amperes             in Watts               Amperes                         Amperes
     0                      10,000                 84*                             42*
     90                     8000                   66*                             33
     125                    5200                   43*                             21
     180                    3500                   29*                             14
     250                    2200                   18                              9
                                       Bobcat 250 Power While Welding

                                                             120 V               240 V
                  Weld Current           Total Power         Receptacle          Receptacle
                  In Amperes             in Watts            Amperes             Amperes
                  300                    1000                10                  5
                  250                    3500                31                  15
                  200                    5200                46                  23
                  150                    6700                60                  30
                  100                    8000                70                  35
                  0                      10000               84                  42
                                    Trailblazer 301 Power While Welding

Typical Connections To Supply Standby Power
Generators may be used to provide emergency power to systems normally supplied by other sources of elec-
tricity, but extreme caution must be exercised to properly install the generator. The specific rules for installa-
tion and use of auxiliary generators are established by the National Electrical Code, state, local, and in some
cases OSHA codes. These codes were developed to assure personnel safety - vitally important for any user. It
is the responsibility of the installer to be familiar with and meet all installation requirements. Major require-
ments of the National Electrical Code (1990 edition) for auxiliary power plant installations are (1) overcurrent
protection as required for the generator, (2) proper grounding of the generator, and (3) isolation of the genera-
tor from other sources of power. Additional requirements may be established by state and local codes.
Overcurrent protection is required if a generator is supplying a permanent installation. Fuses or circuit break-
ers are adequate for small auxiliary power plants. Overcurrent protection is generally not required for genera-
tors supplying portable, cord-connected equipment through receptacles mounted on the generator.

                                                    Page 15
Customer-supplied equipment is required if generator is to supply standby power during emergencies or power
outages. Locate the power company service meter (Item 1), and main and branch overcurrent protection (Item
2), and install equipment as shown below.

                                                                                              Y Have only qualified persons
                                                                                                perform these connections
                                                                                                according to all applicable
                                                                                                codes and safety practices.
                                                                                              1    Power Company Service
                                                                                              2    Main and Branch Overcurrent
                . Customer-supplied equipment is required if                                       Protection
                   generator is to supply standby power during                                3    Double-Pole, Double-Throw
                   emergencies or power outages.                                                   Transfer Switch
                                                                                              Obtain and install correct switch.
                              1                                                               Switch rating must be same as or
                                             240 V                                            greater than the branch overcurrent
         120/240 Volt                                                                         4    Circuit Breakers or Fused
            60 Hz                                            120 V                                 Disconnect Switch
         Three-Wire                                                                           Obtain and install correct switch.
                                                     120 V
                                                                                              5    Extension Cord
                                                                  Neutral                     Select as shown in Section 13-11.
                          2                                                                   6    Generator Connections
                                                                                              Connect terminals or plug of ade-
                                          240 V                                               quate amperage capacity to cord.
                                                                                              Follow all applicable codes and
                                                                                              safety practices.
                                                          120 V                               Turn off or unplug all equipment
         Load                                                                                 connected to generator before
                                                  120 V                                       starting or stopping engine. When
                                                                                              starting or stopping, the engine has
                                                                                              low speed which causes low volt-
                                                                                  4           age and frequency.
                    7                                                                         7    Load Connections

                                                                                      Item 4 is not necessary if circuit
                                                                            or        protection is already present in
                                                                                      welding generator auxiliary
                                                                             F1       power output circuit.

                               6                                                  5

                                          240 V

                   120/240 Volt                            120 V
                   Three-Wire                      120 V
                 Generator Output
                   Connection                                     Ground

                                    Standby Power Equipment And Connections

                                                                  Page 16
Selecting Extension Cords
Use the tables below to select extension cords. Use shortest cords possible because long cords may reduce out-
put or cause unit overload.

    Cord Lengths for 120 Volt Loads
    Y If unit does not have GFCI receptacles, use GFCI-protected extension cord.

                                                           Maximum Allowable Cord Length in ft (m) for Conductor Size (AWG)*

                           Load (Watts)            4                6              8             10             12               14

            5                  600                                             350 (106)       225 (68)      137 (42)          100 (30)

            7                  840                               400 (122)      250 (76)       150 (46)      100 (30)          62 (19)

            10                 1200            400 (122)         275 (84)       175 (53)       112 (34)       62 (19)          50 (15)

            15                 1800            300 (91)          175 (53)       112 (34)       75 (23)        37 (11)           30 (9)

            20                 2400            225 (68)          137 (42)        87 (26)       50 (15)        30 (9)

            25                 3000            175 (53)          112 (34)        62 (19)       37 (11)

            30                 3600            150 (46)           87 (26)        50 (15)       37 (11)

            35                 4200            125 (38)           75 (23)        50 (15)

            40                 4800            112 (34)           62 (19)        37 (11)

            45                 5400            100 (30)           62 (19)

            50                 6000             87 (26)           50 (15)

   *Conductor size is based on maximum 2% voltage drop

    Cord Lengths for 240 Volt Loads
    Y If unit does not have GFCI receptacles, use GFCI-protected extension cord.

                                                           Maximum Allowable Cord Length in ft (m) for Conductor Size (AWG)*

                           Load (Watts)            4                6              8             10             12               14

            5                  1200                                            700 (213)      450 (137)      225 (84)          200 (61)

            7                  1680                              800 (244)     500 (152)       300 (91)      200 (61)          125 (38)

            10                 2400            800 (244)         550 (168)     350 (107)       225 (69)      125 (38)          100 (31)

            15                 3600            600 (183)         350 (107)      225 (69)       150 (46)       75 (23)          60 (18)

            20                 4800            450 (137)         275 (84)       175 (53)       100 (31)       60 (18)

            25                 6000            350 (107)         225 (69)       125 (38)       75 (23)

            30                 7000            300 (91)          175 (53)       100 (31)       75 (23)

            35                 8400            250 (76)          150 (46)       100 (31)

            40                 9600            225 (69)          125 (38)        75 (23)

            45                10,800           200 (61)          125 (38)

            50                12,000           175 (53)          100 (31)

   *Conductor size is based on maximum 2% voltage drop

                                                                 Page 17
Engine and Fuel Choices
Rotating type power supplies are used for field erection and fabrication work when no electric power is avail-
able. For this use, a wide variety of internal combustion engines are available. Both liquid-cooled and air-
cooled engines are used. Gasoline is the most popular fuel because of price and availability. Diesel fuel is pop-
ular because of its high flash point. Also, some regulations will permit only diesel fuel for engines used in spe-
cific applications. A good example is the use of diesel engines for welding power sources on offshore drilling
rigs and marine applications. Propane and natural gas are used in some applications because it is cleaner burn-
ing than gasoline. However, they require a special carburetion system. An example of the need for these clean-
er burning fuels is "in plant" maintenance welding.
Engine driven power sources are often equipped with idling devices to save fuel. These devices are automatic
in that the engine will run at a set idle speed until the electrode is touched to the work or a load is sensed on
the auxiliary power outlet. Under idling conditions, the open circuit voltage of the alternator/generator is low.
Touching the electrode to the work energizes a sensing circuit that automatically accelerates the engine to the
operating speed. When the arc is broken, the engine will return to its idle speed after a set time.

                                                                                   The curve shows typical fuel use
                                                                                   under weld or power loads.

                                   1800 RPM


                              0    50    100 150 200 250 300 350 400 450 500
                                    DC WELD AMPERES AT 100% DUTY CYCLE

                                                                                                              193 093

                                               Fuel Consumption
Engine driven power sources are available with many auxiliary features. Units may be equipped with a remote
output control attachment. It may be either fingertip, hand, or foot control operated so that the operator may
take the power source adjustment (contactor, voltage and/or amperage) to the work area while welding.
Other auxiliary features that can be obtained on the engine driven welding machines are: polarity switches (to
easily change from DCEN to DCEP), running hour meters, fuel gauges, battery chargers, high-frequency arc
starters, and volt/ampere meters. Some larger units are equipped with an air compressor for carbon arc air cut-
ting and gouging, plasma arc cutting and gouging, and operating pneumatic hand tools.

                                                    Page 18
Why Buy A Diesel Engine Powered Welder?
- It uses approximately half as much fuel as a similar sized gasoline engine.
- It has no points, plugs, condenser or carburetor, which means no downtime from costly tune-ups and
- It doesn't have carburetor icing problems in severe cold climates or fuel and vapor lock problems in severe
  warm climates.
- It is less apt to be pilfered for personal use than gasoline due to lack of diesel fueled automobiles, and it's a
  more common fuel for the large construction machinery.
- It will be running long after a gasoline engine has had to be overhauled.
- It is safer fuel to use than gasoline, which is very important on construction job sites, on offshore rigs and in
  the oil fields.

                                                     Page 19

To top