Alternator & Regulator: Operation

The voltage regulator controls field current with a Pulse Width Modulated (PWM) signal, measured in percent of duty cycle. The PWM signal continuously cycles on and off. Pulse width can vary within each cycle.

When ignition switch is turned to RUN position, before engine is started, BCM applies voltage to regulator. Regulator is now in field strobe function and applies a small percentage of duty cycle to field winding, which produces a magnetic field. As alternator RPM increases, field strobe function is disabled and normal regulation occurs.

The regulator switches field current on and off at a fixed frequency of about 400 cycles per second. By varying pulse width, correct average field current for system voltage control is achieved. At high speeds, time on may be 10 percent. At low speeds with a heavy electrical load, time on may be as much as 90 percent.

The BCM monitors the regulator from the alternator field terminal. If the PWM duty cycle falls below 7 percent, the BCM senses a fault, and indicates a problem by lighting the warning lamp on the IPC.