Cummins/Onan — Testing Main Stator Windings
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Some generators have ground connections to the frame. Check wiring diagram.
Procedure
- Testing For Open or Shorted Windings: Use a Wheatstone bridge or ohmmeter having at least 0.001 ohm precision.
- Measure electrical resistance across each pair of stator leads. Proper resistance values are in Table 5-1. All resistances should be ±10% of value shown at 68°F (20°C).
- If a winding is shorted, open or grounded, replace stator assembly. Before replacing, check leads for broken wires or insulation.
- Testing For Grounds: Use a Megger or insulation resistance meter that applies 500 VDC or more.
- Disconnect all stator leads and winding taps from terminals. Measure electrical resistance between any stator lead and stator laminations. Replace stator if insulation resistance is less than 1 megohm
Tools required
- Wheatstone bridge Amazon
- ohmmeter with at least 0.001 ohm precision Amazon
- Megger or insulation resistance meter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Resistance values in Table 5-1
- at 68°F (20°C), ±10%
- 1 megohm
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.