Cummins/Onan — Testing Exciter 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
- Disconnect main rotor field leads at F1+ and F2-.
- Disconnect lead wires from diodes CR1 through CR6.
- Test between exciter lead pairs T1-T2, T2-T3 and T1-T3; resistance at 77°F (25°C) should be 645 milliohms ± 10%.
- For grounds, apply test leads between any CR lead and rotor laminations with insulation resistance meter or Megger not more than 500 volts.
- Reading should be 100,000 ohms or higher. If not, rotor is questionable and may require oven drying and retest.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 645 milliohms ± 10% at 77°F (25°C)
- 100,000 ohms or higher
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.