When a self-excited alternator's field has lost its residual magnetism due to a prolonged idle period, it will fail to produce a voltage. Flashing the field is the procedure used to restore the residual magnetism. Using a 12 volt storage battery, how is this performed?
⢠Residual magnetism must be restored in the alternatorâs magnetic field, not in the armature/stator windings ⢠Difference between field leads (F+ / F-) and stator or sensing leads (S+ / S-) in a selfâexcited alternator ⢠Importance of correct polarity when using a DC battery to establish residual magnetism
⢠Ask yourself: Which winding actually creates the magnetic field that needs its magnetism restoredâthe field winding or the stator? Which letter designation in the choices (F or S) corresponds to that? ⢠Think about what happens if you reverse the polarity when you first magnetize iron with a DC source. Would that help or oppose the normal operating polarity of the alternatorâs field? ⢠In normal operation, the regulator applies DC to which terminals, and with what polarity? Flashing should imitate that condition briefly.
⢠Verify you are applying the 12âvolt battery across the field winding (F+ / F-), not across the stator/sensing leads ⢠Check that the battery positive is connected to the lead that is normally positive for the field, and battery negative to the normally negative lead ⢠Ensure the procedure is a brief application of DC to the correct field terminals, just enough to re-establish residual magnetism, not a continuous connection.
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