Cummins/Onan PCC Control 3100 Series — Testing the PMG
Testing & diagnosis · Permanent Magnet Generator (PMG)
For the Cummins/Onan PCC Control 3100 Series, from the Cummins/Onan service manual.
Applies to: Cummins/Onan DFAA, Cummins/Onan DFAB, Cummins/Onan DFAC, Cummins/Onan DFBF, Cummins/Onan DFCB, Cummins/Onan DFCC, Cummins/Onan DFCE, Cummins/Onan DFE
Before you start
- HIGH VOLTAGE. Touching uninsulated high voltage parts inside the control and power output boxes will result in severe personal injury or death.
Procedure
- Disconnect plug J10 from the voltage regulator output stage module.
- Start the engine at the set and let the speed stabilize.
- Measure voltage across lead pairs J10-1 & J10-4, J10-4 & J10-5, and J10-5 & J10-1.
- Voltage should be at least 150 VAC for 50 Hz sets and at least 180 VAC for 60 Hz sets, approximately the same for each set of leads.
- If voltages are low or uneven, check all leads and connections between A37 and the PMG and repair as necessary.
- Stop the set and measure electrical resistance across lead pairs J10-1 & J10-4, J10-4 & J10-5, and J10-5 & J10-1 with a Wheatstone bridge or digital ohmmeter.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- PMG stator resistance: HC4 = 2/6 ohms; HC5/HC6/HC7 = 4.6 ohms
Full service-parts list: Cummins/Onan DFBF →, Cummins/Onan DFCC →, Cummins/Onan DFCE →, Cummins/Onan DFE →
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.