Cummins/Onan — Generator Tests (Exciter and Alternator)
Testing & diagnosis
From a Cummins/Onan owner's manual covering: 150UK2XN1A, 150UK5XN1A, 150UK6XN1A. Check it applies to your exact model before use.
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Before you start
- Do not connect 480 volt current directly to the E1 and E2 exciter terminals.
- Limit test voltage application to one minute or less.
- Use extreme care not to overheat a rectifier if working on a soldered connection.
- Note carefully the direction of mounting of any rectifier removed; it must be remounted in its original direction.
Procedure
- Temporarily disconnect leads E1, E2, AF1, and AF2 from the terminal block. Connect a substitute ac power source (normal line voltage) of correct voltage per exciter wiring diagram. Limit test voltage
- Check that no component or terminal of the exciter shows a grounded circuit.
- If dc voltage is present at terminals AF1 and AF2 in step 1, check the alternator for grounds, opens, etc.
- Connect exciter leads. If ac voltage drops under load, check exciter rectifiers with a low voltage battery powered ohmmeter. Disconnect one lead from or remove each rectifier. Note direction of mounti
Tools required
- Multimeter type ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Source: Cummins/Onan owner's 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.