Cummins/Onan — Testing Generator Rotor
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDKAD, Cummins/Onan MDKAE, Cummins/Onan MDKAF
Procedure
- Remove rotor leads F1+ and F2- from rotating rectifier assemblies.
- For grounds, connect test leads between F1+ and rotor shaft, then F2- and rotor shaft. Meter should register 100,000 ohms or greater.
- If less than 100,000 ohms, rotor is questionable; oven dry and retest.
- For open or shorted windings, use digital ohmmeter to check resistance between F1 and F2 leads.
- For 12/15 kW genset, resistance at 77°F (25°C) is 2.35 ohms ± 10%.
- For 16/20 kW genset, resistance at 77°F (25°C) is 2.55 ohms ± 10%.
- Replace defective rotor with new identical part.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 100,000 ohms or greater
- 2.35 ohms ± 10% at 77°F (25°C) for 12/15 kW
- 2.55 ohms ± 10% at 77°F (25°C) for 16/20 kW
Full service-parts list: Cummins/Onan MDKAD →, Cummins/Onan MDKAE →, Cummins/Onan MDKAF →
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.