Test 8 - Resistance Check Of Rotor Circuit; Test 9 - Check Brushes And Slip Rings - Generac Power Systems 7 kW NG Repair Manual

Section 2.4
Diagnostic Tests
Note: Stator winding resistance values are very low
and some VOM's will not read such a low resistance,
and will simply indicate CONTINUITY. The manufacture
recommends a high quality digital type meter capable of
reading a very low resistance.
Results
1. Resistance Test: If the VOM indicated a very high resistance
or INFINITY, the windings are open or partially open.
2. Grounded Condition: Any resistance value other than
INFINITY indicates a grounded winding.
3. Shor ted Condition: Any resistance value other than
INFINITY indicates a shorted winding.
Note: Read Section 1.5, "Testing, Cleaning and Drying"
carefully. If the winding tests good, perform the insulation
resistance test. If the winding fails the insulation
resistance test (using a meg-ohm-meter), clean and dry
the stator as outlined in Section 1.5. Then, repeat the
insulation resistance test. If the winding fails the second
resistance test (after cleaning and drying), replace the
stator assembly.
TEST 8 – RESISTANCE CHECK OF ROTOR
CIRCUIT
Discussion
During the rotor amp draw test in Test 4, if the amp draw was
zero, then an OPEN circuit should be present on Wires 4 and
0. This test will verify if the readings were accurate and verify
the field boost circuit.
Identify C1 Connector wiring configuration. Refer to Figure 54.
Configuration A: follow Steps 1-11
Configuration B: follow Steps 1-6
Procedure
1. Remove the 7.5 amp fuse from the control panel.
2. Remove the cover and controller to expose the lower
harness connections.
3. Disconnect the J5 connector from the controller
4. Set the Volt-Ohm-Milliammeter (VOM) to measure
resistance.
5. Connect one-meter test to lead to J5 Pin 13 (Wire 4) and
connect the other meter test lead to J5 Pin 12 (Wire 0),
measure and record the resistance.
6. Connect one-meter test to lead to J5 Pin 13 (Wire 4) and
connect the other meter test lead to a clean frame ground,
measure and record the resistance.
a. If the meter indicated the correct Rotor resistance
values as stated in the front of the manual, proceed to
Step 9.
b. If the meter indicated INFINITY, proceed to Step 7.
Page 54
PART 2
7. If testing C1 Configuration A, locate and disconnect the
bulkhead C1 connector. If testing C1 Configuration B,
stop test and refer to Test 8 Results.
8. Connect one-meter test lead to C1 Pin 5 (Wire 4) and
connect the other meter test lead to C1 Pin 6 (Wire 0),
measure and record the resistance. If the VOM indicated
INFINITY, stop testing and refer back to flow chart (Rotor
Circuit Failure).
9. Locate the starter contactor relay (SCR) and disconnect
Wire 56 (blue wire).
10. Disconnect the J4 connector from the controller.
11. Connect one meter test lead to the disconnected Wire 56
and connect the other meter test lead to J5 Pin 13 (Wire 4).
Measure and record the resistance.
Results
Refer to the front of this manual for correct Rotor resistance
values.
1. If the VOM indicated the correct resistance values in Steps
5, 6, 8, and 11, refer back to flowchart (Good).
2. If the VOM indicated INFINITY in Step 8, refer back to
flowchart (Rotor Circuit Failure).
3. If the VOM indicated the correct resistance in Step 8 and
indicated INFINITY in Step 5, repair or replace Wires 4 and
0 between the C1 and the J5 connector.
4. If the VOM indicated the correct resistance in Step 8 and
indicated INFINITY in Step 5, but indicated the correct
resistance in Step 6, repair or replace Wire 0 between the
J5 connector and the ground connection.
5. If the VOM indicated the correct resistance in Step 5 and
indicated INFINITY in Step 11, replace the harness (Field
Boost Circuit Failure).
TEST 9 – 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.
Refer to Figure 54 to identify the C1 Connector wiring
configuration of the unit being tested.
Configuration A or Configuration B accordingly.
AC GENERATORS
Follow steps for