Alternator & Regulator: Description

Bosch conventional 3-phase, self-rectifying type alternators use 3 exciter diodes connected to stator windings. These diodes turn off alternator indicator light and supply power to voltage regulator while engine is running. Bosch regulators are transistorized and integral with alternator.

An unloader relay is used on the 525i and 535i series. With ignition on and engine off, the relay receives battery voltage (B+) through fuse No. 28 and is grounded through terminal D+ of the alternator. The relay energizes and switches ground to some accessories. When the engine is running and the alternator begins to charge, battery positive voltage is also applied to terminal D+ to switch off the relay.