Kohler — Separate Excitation Procedure
Testing & diagnosis · Rotor/alternator
From a Kohler service manual covering: 12RES, 8.5/12 RES, 8.5RES. Check it applies to your exact model before use.
Applies to: Kohler 12RES, Kohler 8.5RES, Kohler CH20 engine, Kohler CH 740 engine
Before you start
- Hazardous voltage. Open the main circuit breakers of all power sources before servicing the equipment.
Procedure
- Disconnect the black FN and FP leads from the alternator at the SCR module (+) and (--) terminals.
- Connect a DC ammeter, 20-amp fuse, and a 12-volt automotive battery to the FP and FN brush leads.
- Note and record the ammeter reading (should be battery voltage divided by specified rotor resistance).
- Start the engine and check that the ammeter reading remains stable.
- An increasing reading indicates a shorted rotor; a reading decreasing to zero or unstable suggests a running open.
- Check for AC output across the stator leads and compare to specifications.
- If rotor and stator are good, check the wiring and fuses and check the SCR module.
- Check the controller settings and connections.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Example rotor current: 12 volts / 4 ohms = 3 amps
Full service-parts list: Kohler 12RES →, Kohler 8.5RES →
Source: Kohler 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.