GM Service Manual Online
For 1990-2009 cars only

Generator

The generator features the following major components:

    • The delta stator
    • The rectifier bridge
    • The rotor with slip rings and brushes
    • A conventional pulley
    • Dual internal fans
    • The regulator

The pulley and the fan cool the slip ring and the frame.

The generator features permanently lubricated bearings. Service should only include tightening of mount components. Otherwise, replace the generator as a complete unit.

Regulator

The voltage regulator controls the rotor field current in order to limit the system voltage. When the field current is on, the regulator switches the current on and off at a rate of 400 cycles per second in order to perform the following functions:

    • Radio noise control
    • Obtain the correct average current needed for proper system voltage control

At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

Circuit Description

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

When the ignition is in the RUN position battery voltage is supplied through the Ignition 1 relay to the generator , turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator uses the voltage sense circuit from the underhood fuse block to varie the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. .

Charge Indicator

The charge indicator is a LED located in the I/P cluster. It receives battery voltage when the ignition is in the RUN position. The circuit is grounded through the L terminal of the generator.

The generator will ground the L terminal when the regulator detects one of the following conditions:

    • Sense voltage below 9.5 V
    • No AC voltage detected