BOLT 8T4971 - Caterpillar

The electrical system has an insulated return system. The charging circuit operates when the engine is running. The alternator in the charging circuit produces direct current for the electrical system.Starting Motor
Illustration 1 g01216877
Typical example12 Volt or 24 Volt Starting Motor (1) Terminal for connection of the ground cable (2) Terminal 30 for connection of the battery cable (3) Terminal 50 for connection of the ignition switchThe starting motor turns the engine via a gear on the engine flywheel. The starting motor speed must be high enough in order to initiate a sustained operation of the fuel ignition in the cylinders.The starting motor has a solenoid. When the ignition switch is activated, voltage from the electrical system will cause the solenoid to move the pinion toward the flywheel ring gear of the engine. The electrical contacts in the solenoid close the circuit between the battery and the starting motor just before the pinion engages the ring gear. This causes the starting motor to rotate. This type of activation is called a positive shift.When the engine begins to run, the overrunning clutch of the pinion drive prevents damage to the armature. Damage to the armature is caused by excessive speeds. The clutch prevents damage by stopping the mechanical connection. However, the pinion will stay meshed with the ring gear until the ignition switch is released. A spring in the overrunning clutch returns the clutch to the rest position.Air Starting Motor
Illustration 2 g01675493
Typical exampleThe air starting motor is a nonserviceable component. The correct air supply must be provided to the air starting motor. Refer to Specifications, "Air Starting Motor" for more information.Alternator
The electrical outputs of the alternator have the following characteristics:
Three-phase
Full-wave
RectifiedThe alternator is an electro-mechanical component. The alternator is driven by a belt from the crankshaft pulley. The alternator charges the storage battery during the engine operation.The alternator is cooled by an external fan which is mounted behind the pulley. The fan may be mounted internally. The fan forces air through the holes in the front of the alternator. The air exits through the holes in the back of the alternator.The alternator converts the mechanical energy and the magnetic field into alternating current and voltage. This conversion is done by rotating a direct current electromagnetic field on the inside of a three-phase stator. The electromagnetic field is generated by electrical current flowing through a rotor. The stator generates alternating current and voltage.The alternating current is changed to direct current by a three-phase, full-wave rectifier. Direct current flows to the output terminal of the alternator. The direct current is used for the charging process.A regulator is installed on the rear end of the alternator. Two brushes conduct current through two slip rings. The current then flows to the rotor field. A capacitor protects the rectifier from high voltages.The alternator is connected to the battery through the ignition switch. Therefore, alternator excitation occurs when the switch is in the ON position.