Rotor Field Winding Test
- Check rotor for grounds or an open circuit, using a 110-volt test lamp or an ohmmeter. See Fig 1. To check for grounds, connect ohmmeter leads to shaft and slip ring (each ring in turn). No continuity should exist.
- To test for open field, connect ohmmeter leads to each slip ring. Continuity should be indicated.
- To test for shorts, connect a 12-volt battery and ammeter in series with both slip rings. Current draw is used for this test.
- Resistance should be 2.5-3.0 ohms. Excessive amperage draw or low resistance indicates shorted windings. If rotor tests okay, but alternator output is low, continue with tests.