SPRING 7W5081 - Caterpillar

Illustration 1 g00669869
21-SI AlternatorThe alternator is an electronic component that is belt driven. The alternator is used to charge the storage battery during engine operation. The alternators that are covered by this manual are cooled by air that is drawn through the alternator by the external fan. Air is drawn through baffles that are located in the rear cover. The air then exits from the drive end frame behind the fan.The alternator converts a combination of mechanical energy and magnetic energy to alternating current and voltage. This is done by rotating a direct current electromagnetic field on the inside of the three-phase stator. The alternating current and voltage are generated by the stator. The current and the voltage are changed to direct current by the three-phase full wave rectifier. The rectifier uses six silicon rectifier diodes. The alternator also has a diode assembly which rectifies field current. The field current is necessary for alternator output.Voltage regulation is accomplished by the regulator that is located in the back of the alternator. The regulator controls current flow to the field coil on the rotor. The current passes from the regulator to the field coil through two brushes that contact two slip rings. The two slip rings that are located on the rotor shaft are electrically connected to the field coil.The capacitor that is located in the back of the alternator protects the rectifier and diode assembly from high voltages. The capacitor also suppresses electrical noise.An "I" terminal is located on the end of the following alternators.
117-1379 Alternator Gp
132-2156 Alternator Gp The "I" terminal is connected internally to the field circuit. An indicator light that is connected in series with the terminal will glow when there is a difference between the terminal voltage and the battery voltage. When the system is charging properly, the light is off.