Generac Power Systems CorePower 6/7 kW 60 Hz Diagnostic Repair Manual page 37

AC GENERATORS
TEST 6 – RESISTANCE CHECK OF ROTOR
AND ROTOR CIRCUIT
Procedure A
1. Locate and disconnect the Red (Wire 4) and White (Wire
1) [Red and Black on CorePower] wires from the voltage
regulator.
2. Set a Volt-Ohm-Meter (VOM) to measure resistance.
3. Connect meter test leads across the Red (Wire 4) and White
(Wire 1) [Red and Black on CorePower] wires leading to the
brush assembly disconnected in Step 1. Measure and record
the resistance.
Results
1. If the VOM indicated a resistance of approximately 50 ohms
±20 ohms (40 ohms ± 20 ohms on CorePower), refer back
to flow chart.
2. If the VOM did not indicate the proper resistance, go to Step
4.
Procedure B
1. Locate and remove the brush assembly. Refer to Section 5.1
"Major Disassembly."
2. Set a Volt-Ohm-Meter (VOM) to measure resistance.
3. Connect meter test leads across the two exposed slip rings.
Measure and record the resistance.
Results
1. If the VOM indicated a resistance of approximately 50 ohms
±20 ohms (40 ohms ± 20 ohms on CorePower), verify rotor
amp draw.
2. If the VOM did not indicate the proper resistance, refer back
to flow chart.
TEST 7 – CHECK BRUSHES AND SLIP RINGS
Discussion
The brushes and slip rings function to provide an electrical
connection for excitation current from the stationary components
to the rotating rotor. Made of a special long lasting material,
brushes seldom wear out or fail. However, slip rings can develop
a tarnish or film that can inhibit or offer a resistance to the flow of
current. Such a non-conducting film usually develops during non-
operating periods. Broken or disconnected wiring can also cause
loss of excitation current to the rotor.
Procedure
1. Disassemble the Generator until the brushes and slip rings
are exposed. Refer to Section 5.1 "Major Disassembly."
2. Inspect the brush wires and verify they are secured and
properly connected.
3. Inspect the brush assembly for excessive wear, or damage.
PART 2
4. Inspect the rotor slip rings. If their appearance is dull or
tarnished, polish with a fine grade abrasive material.
Do not use metallic grit to polish slip rings. This may

cause irreversible damage to the rotor.
5. The Red and White (Red and Black on CorePower) wires,
located on the brush terminals, provide an electrical
connection to the voltage regulator. To test these wires for
an OPEN condition, remove the Red and White (Red and
Black on CorePower) wires from the brush assembly and
disconnect the connector containing Wires 2, 6, S1 and S2
from the voltage regulator.
6. Set Volt-Ohm-Meter (VOM) to measure resistance.
7. Connect one meter test lead to the White (Wire 1) wire at the
brush assembly and connect the other meter test lead to the
White (Wire 1) wire disconnected at the voltage regulator.
Measure and record the Resistance.
8. Connect one meter test lead to the Red (Wire 4) wire
disconnected at the brushes and the other meter test lead to
the Red (Wire 4) wire disconnected at the voltage regulator.
Measure and record the Resistance.
Results
1. Repair or replace any damaged wires as necessary.
2. Replace damaged brush holder if necessary.
3. Clean and polish slip rings as required.
4. Reconnect all wires.
TEST 9 – TEST THE STATOR
Discussion
This test will use a Volt-Ohm-Meter (VOM) to test the stator
windings for the following faults:
• An OPEN circuit condition
• A "short-to-ground" condition
• A short circuit between windings
Tables 10 and 11 are provided to record the results of the following
procedure. These results may be required when requesting factory
support.
Additional copies of Tables 10 and 11 can be found in Appendix A
"Supplemental Worksheets" at the back of this manual.
Note: It is the recommendation of the factory to perform this
test procedure using appropriate probe adapters on the wire
side of the connector. Testing inside the connector itself
(front-probing) can cause damage resulting in poor or loose
connections.
Section 2.4
Diagnostic Tests
Page 35