Cummins/Onan QST30 — Testing the PMG
Testing & diagnosis
For the Cummins/Onan QST30, from the Cummins/Onan service manual.
Applies to: Cummins/Onan DFHA, Cummins/Onan DFHB, Cummins/Onan DFHC, Cummins/Onan DFHD, Cummins/Onan QST30, Cummins/Onan QST30 engine
Before you start
- HAZARDOUS VOLTAGE. Use insulated tools and dry insulating mat.
Procedure
- Disconnect plug J10 from voltage regulator output stage module.
- Start engine and let speed stabilize.
- Measure voltage across J10-1 & J10-4, J10-4 & J10-5, J10-5 & J10-1. Should be at least 150 VAC for 50 Hz, 180 VAC for 60 Hz.
- Stop set and measure resistance across same lead pairs. Should be 2.6 ±10% ohms for P7 and HC6.
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
- PMG voltage at least 150 VAC for 50 Hz sets
- PMG voltage at least 180 VAC for 60 Hz sets
- PMG resistance 2.6 ±10% ohms for P7 and HC6
Full service-parts list: Cummins/Onan DFHA →, Cummins/Onan DFHB →, Cummins/Onan DFHC →, Cummins/Onan DFHD →, Cummins/Onan QST30 →
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.