GM Service Manual Online
For 1990-2009 cars only

Charging Circuit Operation

The generator provides voltage to operate the electrical system and to charge the battery. A magnetic field is created when current flows through the rotor windings. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is then converted to a DC voltage by a rectifier bridge. This DC voltage is then supplied through circuit  1 to the electrical system at the battery terminal.

The amount of output voltage is controlled by the current supplied to the rotor. The solid state regulator in the generator controls the current supplied to the rotor. The rotor current is a series of electrical pulses supplied by the regulator. When the ignition switch is first placed in the RUN position, the pulse width is very narrow. This causes the rotor to produce a weak magnetic field. This will produce a lower output voltage to the vehicle's electrical system. Once the engine is running, the regulator monitors the output voltage through an internal wire and changes the pulse width accordingly.