Cummins/Onan — Testing Generator Stator

Testing & diagnosis

From a Cummins/Onan service manual — check it applies to your exact model before use.

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Procedure

1. Before testing stator, disconnect control wires 4, 7, 8, 9, and 10 from TB21. Isolate from ground and each other.
2. Connect all stator output leads (T1-T12) together. Use ohmmeter set on R x 100 scale and measure insulation resistance between windings and stator frame.
3. A reading of less than one megohm indicates a ground. Field circuit breaker can be either open or closed for this test.
4. Testing for Shorts: Refer to electrical schematic to determine individual coil lead wires. Disconnect instrumentation leads and stator leads T4, T7, T8, T9, and T10.
5. Connect ohmmeter R x 100 scale to one lead of a stator winding, and other ohmmeter lead to all other stator leads connected together, leaving other end of coil winding being tested open.
6. A reading of less than infinity indicates a short. Repeat until all six coils have been tested.
7. Measure resistance of windings using a Kelvin Bridge meter. Refer to Figure 4-7 and Table 4-1.
8. If any windings are shorted, open, or grounded, replace the stator assembly. Before replacing, check leads for broken wires or damaged insulation.

Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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