Cummins/Onan — Field Winding Tests
Testing & diagnosis · Field (frame) windings
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MCCK
Before you start
- Attach and remove meter leads only when generator set is not operating.
Procedure
- Disconnect the field coil leads from their terminal points on the brush blocks.
- Disconnect the S1 terminal from the start solenoid.
- Ground test: touch one prod to each coil terminal and the other to a clean, paint-free part of the frame.
- If the lamp lights or ohmmeter shows continuity, replace the frame assembly.
- Open test: check the shunt winding resistance between S1 and F2.
- Measure the series winding resistances between S1 and S2, and S1 and S3.
- If resistance is high, an open circuit is likely and the frame assembly should be replaced.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- DC field voltage during no-load operation: 17 volts for LK; 27 to 33 volts for CCK, MCCK and NH
Full service-parts list: Cummins/Onan MCCK →
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.