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Troubleshooting
5. Isolate all main stator leads and measure resistance
across each winding and check each main stator
lead to ground. Compare readings to values in
Alternator Specifi cations table.
a. If winding resistance is out of specifi cation or a
resistance to ground is measured then replace
stator.
1. Use an insulation tester on main stator
windings and verify reading is 500K Ohm or
higher.
2. If insulation tester shows low resistance to
ground then replace alternator.
b. If stator tests pass, proceed to next step.
6. Cut wire on 1 side of each diode.
a. Use a meter set to diode test and check each
diode.
b. If a diode tests bad, replace diode. If diodes pass
test, proceed to next step.
1. Note polarity stripe of diode. Cut other wire of
diode and remove bad diode.
2. Solder in a new diode paying attention to
polarity stripe on diode.
7. Measure resistance value of rotor winding with rotor
leads disconnected from diodes.
a. Compare resistance reading to value in Alternator
Specifi cations table.
b. Check resistance from each rotor lead to rotor
shaft.
1. If resistance of winding is not in specifi cation
or measures resistance from either rotor lead
to rotor shaft, then replace alternator.
2. If rotor checks out fi ne, solder diode wires and
proceed to next step.
8. There is no way to check for a running short or open
circuit in rotor winding. If previous tests pass:
a. Replace capacitor.
b. If replacing capacitor doesn't restore voltage,
replace alternator.
High Output Voltage
1. Verify engine speed is not too high. Adjust no load
speed to 3600 RPM if needed. If speed is correct
proceed to next step.
2. Since there is no voltage sensing circuit on a
capacitor-excited generator:
a. Verify value of capacitor is correct according to
Alternator Specifi cations table.
b. If a larger capacitor is used, output voltage will be
higher than it is supposed to be. Install correct
value of capacitor if found to be wrong.
c. If capacitor is correct then proceed to next step.
3. Check:
a. Resistance values of all stator windings and rotor
winding.
b. Resistance from stator leads to ground.
c. Diodes are good.
1. Cut wire on 1 side of each diode from rotor.
8
2. Use a meter set to diode test and check each
diode.
d. Resistance from rotor leads to rotor shaft.
4. Replace:
a. Any component that does not meet specifi cations
in Alternator Specifi cations table.
b. If diodes are found to be open or shorted.
1. Note polarity stripe of diode. Cut other wire of
diode and remove bad diode.
2. Solder in a new diode paying attention to
polarity stripe on diode.
c. Any windings have resistance to ground.
5. If previous tests pass:
a. Solder diode wires that were cut.
b. Replace capacitor.
c. If replacing capacitor doesn't restore voltage,
replace alternator.
Alternator Can't Output Rated Power
1. Verify that engine speed at full load is at 3600 RPM.
a. At no load it should be at 3600 RPM. Adjust
engine speed if needed.
b. If engine speed drops below 3600 RPM before
full load is achieved, then troubleshoot engine for
lack of power.
c. If speed is correct proceed to next step.
2. Take a current reading of all loads and add together
and multiply by output voltage to confi rm that total
wattage of load being applied does not exceed rating
of generator.
a. Reduce load if exceeding rating of generator.
b. If loading is not an issue, proceed to next step.
3. Use a load bank and apply load, watch output
voltage of unit as load is increased.
If output voltage starts dropping and engine speed
has not dropped below 3600 RPM:
a. Check resistances of all stator and rotor windings.
If resistance readings do not meet specifi cation,
replace defective alternator.
b. Use an insulation tester on rotor and stator
windings and verify readings are 500K Ohm or
higher. Replace defective alternator.
c. If a diode tests bad, replace diode. If diodes pass
test, proceed to next step.
1. Note polarity stripe of diode. Cut other wire of
diode and remove bad diode.
2. Solder in a new diode paying attention to
polarity stripe on diode.
4. If previous tests pass:
a. Replace capacitor.
b. If replacing capacitor doesn't restore voltage,
replace diodes.
c. If replacing diodes doesn't restore voltage,
replace alternator.
KohlerPower.com
38 690 01 Rev. --
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