Detroit Diesel — Separate Excitation
Testing & diagnosis · Alternator
From a Detroit Diesel service manual — check it applies to your exact model before use.
Before you start
- Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.
Procedure
- Disconnect all leads from the voltage regulator.
- Disconnect the FP/FN connector.
- Disconnect exciter field winding leads; measure resistance with an ohmmeter.
- Connect separate excitation circuit; connect DC ammeter in series with FP and record reading.
- Move master switch to RUN to start the generator set.
- Check ammeter values; unstable reading indicates short or running open in exciter field.
- Check AC output across stator main windings and compare to Section 1 specifications.
- Move master switch to OFF/RESET to stop the generator set.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Exciter field current = battery voltage divided by specified cold exciter field winding resistance
Source: Detroit Diesel 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.