Cummins/Onan — Alternator Output Test
Testing & diagnosis · Flywheel alternator / regulator-rectifier
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan Performer P224 engine
Before you start
- Do not reverse battery leads. Do not allow engine to run without being connected to the alternator.
Procedure
- Check battery voltage with unit not running. If not within 12 to 13 VDC, charge battery.
- With engine running, check battery terminal voltage (regulator output). Should be 13.6 to 14.7 VDC.
- If greater than specified, replace regulator-rectifier assembly; if less, check wires, connections and fuses.
- Disconnect both AC stator leads and test AC voltage at stator leads with engine running. Should be 57 VAC.
- Use the Rx1 scale to check stator for open or ground. Stator winding resistance should be 0.01 to 0.19 Ohms.
Tools required
- Volt-ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Battery terminal voltage 13.6 to 14.7 VDC
- Stator AC voltage 57 VAC
- Stator winding resistance 0.01 to 0.19 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.