G3B, K3A and L3A Denso Alternators Caterpillar

As the alternator begins operating, the IC regulator detects battery voltage that is applied to the ignition terminal. The initial exciting current then flows through the rotor coil. When the ignition switch is turned ON the regulator turns on and off. This occurs intermittently in order to reduce battery discharge. Current is kept to a minimum of approximately 0.17 amperes.

During this time, the generator is not running and no electricity is generated. Voltage at the "P" terminal is zero. After the engine is started and rpm rises, the excitation circuit is turned on all the time, and generated voltage rises rapidly. When the voltage at the "B" terminal exceeds the battery voltage current flows into the battery.

The voltage regulator turns ON the field current and the voltage regulator turns OFF the current many times in one second in order to keep the voltage at a preset level.