Cummins/Onan — Exciter Rotor
Testing & diagnosis
From a Cummins/Onan service manual covering: 300.0 DFT, 350.0 DFU, 350.0 WF, 400.0 DFV, 400.0 WK, 450.0 DFW, 500.0 DFY, 600.0 DWV. Check it applies to your exact model before use.
Applies to: Cummins/Onan YB series
Procedure
- Use a Kelvin bridge instrument for this test.
- Remove rotating diodes CR1, CR2, CR3 from heat sinks.
- Measure resistance of rotor windings. Should be within 0.1463- to 0.1788-ohms at 20°C (68°F).
- Replace rotating diodes on heat sinks. Hold body with wrench while torquing to 15 lb-in (1.7 N·m).
- Using ohmmeter on R x 10K, measure between any rotating diode lead and generator frame. Less than infinity indicates low insulation.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 0.1463- to 0.1788-ohms at 20°C (68°F)
- 15 lb-in (1.7 N·m)
Full service-parts list: Cummins/Onan YB series →
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.