Cummins/Onan — Servicing the PMG - Testing
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Hazardous voltage - touching uninsulated high voltage parts 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; release the Start switch as soon as the engine fires.
- Measure voltage across lead pairs P2-P3, P3-P4 and P4-P2; should be at least 150 VAC for 50 Hz sets and 180 VAC for 60 Hz sets.
- Stop the set and measure resistance across each lead pair; each winding should be approximately 4.4 ohms.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 150 VAC (50 Hz)
- 180 VAC (60 Hz)
- 4.4 ohms
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.