Cummins/Onan — Testing the Generator (Rotor and Stator)
Testing & diagnosis · Generator rotor and stator
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan Performer P224 engine
Before you start
- Many troubleshooting procedures present hazards that can result in severe personal injury or death. Only qualified service personnel should perform service.
Procedure
- Test field flash voltage at brush holder terminals with engine cranking; check for 12 VDC.
- If not present, disconnect F1 and F2 leads and check for 12 VDC while cranking engine.
- Test rotor grounds between each slip ring and rotor shaft (Megger at 500 VDC or more). Reading should be 100,000 ohms or greater.
- Test rotor for open/shorted windings between F1 and F2 leads. Resistance should be 25.47 ohms +/- 10%.
- Isolate stator windings and test for opens and grounds between T1-T2, T3-T4 and Q1-Q2.
- Resistance values: T1-T2 0.095 ohms, T3-T4 0.095 ohms, Q1-Q2 1.185 ohms (+/- 5%).
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
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.