Cummins/Onan — Testing Generator Windings
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDKB, Cummins/Onan MDKBH
Before you start
- Disconnect the negative battery cable before removing a panel or access door.
Procedure
- Disconnect T1, T2, T3 and T4 from the terminals in the output box.
- Disconnect B1 and B2 from charging regulator AVR1.
- Disconnect Q1 and Q2 from controller A1 by pulling green connector P3 (Pins 4 and 5).
- Measure resistance across each winding lead pair and replace the stator if any winding is open (zero ohms).
- Use a meter with 0.001 ohm precision to compare each winding resistance to Table 8-1.
- For the rotor field, disconnect field leads F1 and F2 by pulling green connector P3 and measure resistance across pins 7 and 8.
- Using a megger, measure resistance between the rotor and either slip ring; replace if less than one megohm.
- Measure resistance between the stator stack and each stator lead; replace if less than one megohm.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
Full service-parts list: Cummins/Onan MDKB →, Cummins/Onan MDKBH →
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.