Cummins/Onan — Flywheel Alternator Output Test
Testing & diagnosis · Flywheel alternator charging system
From a Cummins/Onan service manual covering: P216, P218, P220, P248. Check it applies to your exact model before use.
Applies to: Cummins/Onan P216, Cummins/Onan P218, Cummins/Onan P220, Cummins/Onan P248
Before you start
- Reversing positive and negative battery connections or allowing the engine to run without being connected to the alternator will result in engine electrical system damage.
Procedure
- Check the battery voltage with the engine not running; charge the battery if not within Table 8-1 specifications.
- With the engine running, check battery terminal voltage (regulator output) using a DC voltmeter.
- If voltage is greater than specified, replace the regulator-rectifier assembly; if less than specified, proceed to Step 3.
- Examine all wires for loose, corroded, or broken connections and check fuses; repair as needed to assure complete circuits.
- Disconnect the plug from the regulator-rectifier and test AC voltage at the plug with the engine running.
- If AC voltage is as specified but DC voltage is low, replace the regulator-rectifier.
- Use the Rx1 scale on the ohmmeter to detect an open or ground in the stator (engine not running); the reading to ground should show no continuity.
- Connect one ohmmeter lead to each wire from the stator and check resistance; replace the stator if not as specified.
- If stator resistance is as specified and windings are not shorted or open, low AC voltage may be due to loss of magnetism; replace the blower wheel assembly.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 20-amp FridayParts $27.99 system: battery 12 to 13 VDC, regulator 13.6 to 14.7 VDC, stator 29 VAC @ 1800 rpm (approx) / 57 VAC @ 3600 rpm (approx), stator resistance 0.10 to 0.19 ohms
- 35-amp system: battery 12 to 13 VDC, regulator 13.6 to 14.7 VDC, stator 24 VAC @ 1800 rpm (approx) / 47 VAC @ 3600 rpm (approx), stator resistance 0.06 to 0.10 ohms
Full service-parts list: Cummins/Onan P216 →, Cummins/Onan P218 →, Cummins/Onan P220 →, Cummins/Onan P248 →
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.