Cummins/Onan — Testing Generator Rotor [B]
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan HDKA, Cummins/Onan HDKAQ, Cummins/Onan HDKAR
Procedure
- Isolate the rotor windings by disconnecting the two leads to the brush holder.
- Testing for grounds: connect test leads between each ring and the rotor shaft in turn; meter should register 100,000 ohms or greater.
- If less than 100,000 ohms, thoroughly dry the rotor and retest; replace a grounded rotor with a new identical part.
- Testing for open/shorted windings: check resistance between F1 and F2 slip rings with an ohmmeter.
- Rotor resistance 60 Hz is 18.2 ohms; 50 Hz is 20.7 ohms (10% at 25 C).
- If there is a large difference, replace the defective rotor with a new, identical part.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Ground: 100,000 ohms or greater
- 60 Hz rotor 18.2 ohms
- 50 Hz rotor 20.7 ohms
Full service-parts list: Cummins/Onan HDKA →, Cummins/Onan HDKAQ →, Cummins/Onan HDKAR →
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.