WARNING: To avoid a battery explosion, ensure carbon pile tester is off before connecting it to battery.

Mount generator on test stand. Ensure ground polarity of generator and battery are the same. Connect generator to a fully charged 12-volt battery. Connect voltmeter, ammeter, carbon pile (in OFF position) and 30-500 ohm resistor between battery and generator terminal "L". See Fig 1 .
Slowly increase generator speed and observe voltmeter reading. If voltage is less than 16 volts, go to next step. If voltage is uncontrolled and increases to more than 16 volts, rotor field is shorted and/or voltage regulator is defective. A shorted rotor field can cause voltage regulator to become defective. Repair as required.
If voltage is less than 16 volts, increase generator speed and adjust carbon pile to obtain maximum current output. Maintain voltage at 13 volts. If maximum current output is within 15 amps of generator rated output, generator is okay. See GENERATOR SPECIFICATIONS table. If maximum current output is not within 15 amps of rated output, repair or replace generator.

Fig 1: Testing Generator Output Using Carbon Pile Tester

Courtesy of ISUZU MOTOR CO.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Generator Output Test