Alternator: Testing and Inspection

GENERATOR

INSPECTION

1. INSPECT GENERATOR REGULATOR ASSEMBLY




a. Measure the resistance between the regulator terminals (F) and (B).

Standard resistance: Below 1 Ohm or more than 10 kOhms

HINT: When the ohmmeter's leads are initially touched to the regulator, one of the above values will be output. When the leads are reversed, the reading will change to the other value.

If the result is not as specified, replace the generator regulator.




b. Measure the resistance between the regulator terminals (F) and (E).

Standard resistance: Below 1 or more than 10 kOhms

HINT: When the ohmmeter's leads are initially touched to the regulator, one of the above values will be output. When the leads are reversed, the reading will change to the other value.

If the result is not as specified, replace the generator regulator.

2. INSPECT GENERATOR ROTOR ASSEMBLY




a. Check the rotor for an open circuit.
1. Measure the resistance between the slip rings.

Standard resistance: 2.1 to 2.5 at 20 degrees C (68 degrees F)

If the result is not as specified, replace the rotor assembly.




b. Check if the rotor is grounded.
1. Measure the resistance between the slip ring and rotor.

Standard resistance: 10 kOhms or higher

If the result is not as specified, replace the rotor assembly.

c. Check that the slip rings are not rough or scored.
If rough or scored, replace the rotor assembly.




d. Using a vernier caliper, measure the slip ring diameter.

Standard diameter: 14.2 to 14.4 mm (0.559 to 0.567 in.)
Minimum diameter: 12.8 mm (0.504 in.)

If the diameter is less than the minimum, replace the rotor assembly.

3. INSPECT GENERATOR HOLDER WITH RECTIFIER




a. Inspect the positive (+) rectifier.
1. Using an ohmmeter, connect one tester probe to the positive (+) terminal and the other to each rectifier terminal.
2. Reverse the polarity of the tester probes and repeat the step above.
3. Check that one shows a resistance of below 1 and the other shows a resistance of 10 kOhms or higher.
If the result is not as specified, replace the rectifier holder.




b. Inspect the negative (-) rectifier.
1. Using an ohmmeter, connect one tester probe to each negative (-) terminal and the other to each rectifier terminal.
2. Reverse the polarity of the tester probes and repeat the step above.
3. Check that one shows a resistance of below 1 and the other shows a resistance of 10 kOhms or higher.
If the result is not as specified, replace the rectifier holder.

4. INSPECT DRIVE END FRAME




a. Check the stator coil for an open circuit.
1. Measure the resistance between the coil leads.

Standard resistance: Below 1 Ohm

If the result is not as specified, replace the drive end frame.




b. Check the stator for ground.
1. Measure the resistance between the coil lead and drive end frame.

Standard resistance: 10 kOhms or higher

If the result is not as specified, replace the drive end frame.

c. Check that the bearing is not rough or worn.
If necessary, replace the generator assembly.




5. INSPECT GENERATOR BRUSH HOLDER ASSEMBLY
a. Using a vernier caliper, measure the exposed brush length.

Standard exposed length: 9.5 to 11.5 mm (0.374 to 0.453 in.)
Minimum exposed length: 4.5 mm (0.177 in.)

If the exposed length is less than the minimum, replace the brush holder assembly.