1100 SERIES DIESEL TRUCK ENGINE Electrical System Caterpillar

Electrical System

The electrical system is a combination of two separate electric circuits: The charging circuit and the starting circuit. Each circuit is dependent on some of the same components. The battery (batteries), on-off start switch, circuit breaker, ammeter, cables and wires from the battery are common in each of the circuits.


The ignition switch must be ON to allow the electrical system to function. Some charging circuit components will be damaged if the engine is operated with the ignition switch OFF.

The charging circuit is in operation when the diesel engine is operating. The electricity producing (charging) unit is an alternator. A regulator in the circuit senses the state of charge in the battery and regulates the alternator output to keep the batter fully charged.

The alternator has four main components: end frame assembly (brush end), rotor assembly, stator and shell assembly, and end frame assembly (drive end).

A separate regulator senses the charge condition of the battery as well as electrical system power demand and controls the alternator output accordingly by limiting the field current.



Never operate the alternator without the battery in the circuit. Making or breaking an alternator connection with a heavy load on the circuit will sometimes result in regulator damage.

The starting motor is a device used to rotate the flywheel of an engine fast enough to start the engine.



The starting motor includes a solenoid. The solenoid engages the pinion with the ring gear on the engine flywheel, when the solenoid is energized. The pinion always engages before the electric contacts in the solenoid causes the circuit between the battery and the starting motor to close. An overrunning clutch protects the starting motor from being overspeeded. Releasing the start-switch disengages the pinion and flywheel ring gear.

A solenoid is a magnetic switch that uses low current to close a high current circuit. The solenoid is an electro-magnet with a movable core. There are contacts on the end of the core. The contacts are held apart by a spring pushing the core away from the magnetic center of the coil. Low current energizes the coil and forms a magnetic field. The magnetic field pulls the core to the center of the coil, closing the contacts and completing the starting circuit.