Cummins/Onan 3100 series — Servicing the PMG - Testing
Testing & diagnosis · Permanent Magnet Generator (PMG)
For the Cummins/Onan 3100 series, from the Cummins/Onan service manual.
Applies to: Cummins/Onan DGBB, Cummins/Onan DGBC, Cummins/Onan DGCA, Cummins/Onan DGCB, Cummins/Onan DGCC, Cummins/Onan DGDA, Cummins/Onan DGDB, Cummins/Onan DGDK, Cummins/Onan DGEA, Cummins/Onan DGFA, Cummins/Onan DGFC
Before you start
- HAZARDOUS VOLTAGE. Touching uninsulated high voltage parts inside the control and power output boxes can result in severe personal injury or death.
Procedure
- Disconnect leads P2, P3 and P4 from the voltage regulator.
- Start the engine at the set and let the speed stabilize.
- Measure voltage across lead pairs P2-P3, P3-P4 and P4-P2 (at least 150 VAC for 50 Hz, at least 180 VAC for 60 Hz).
- If voltages are low or uneven, check all leads and connections before disassembling the PMG.
- Stop the set and measure electrical resistance across P2-P3, P3-P4 and P4-P2 (approximately 4.4 ohms each winding).
Tools required
- Wheatstone bridge or digital ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- At least 150 VAC for 50 Hz sets
- At least 180 VAC for 60 Hz sets
- Each winding approximately 4.4 ohms
Full service-parts list: Cummins/Onan DGBB →, Cummins/Onan DGBC →, Cummins/Onan DGCA →, Cummins/Onan DGCB →, Cummins/Onan DGCC →, Cummins/Onan DGDA →, Cummins/Onan DGDB →, Cummins/Onan DGEA →, Cummins/Onan DGFA →, Cummins/Onan DGFC →
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.