Car Starters



The starting system consists of a high amperage electric motor, a starter solenoid or starter relay, battery, starter cables, and ignition switch. Engine starting is achieved by use of a high amperage electric motor. When the driver turns the key to the start position, current is supplied to the starter relay or starter solenoid. The relay or starter solenoid closes contacts that complete the circuit from the battery to the starter motor. The high amperage current flows through the starter and causes it to rotate the engine at sufficient speed to allow easy starting. The starter motor rotates the engine by means of a small gear attached to the end of the starter motor.

This gear is called the starter drive. When the starter is operated, the drive extends and contacts the teeth of flywheel gear. The gear ratio of the starter drive gear is about 15/1. That means that the starter motor will complete 15 revolutions while the engine completes one revolution. When the engine starts, the drive must be immediately withdrawn from the flywheel to prevent damage to the starter.

A starter consumes more current than any other electrical device used on a vehicle. In order to ensure an adequate supply of current to the starter, large cables are used to connect the starter to its power source. Voltage is supplied to the starter from the battery through either a remote relay or a starter mounted solenoid. The design of the starter power source depends on the type of drive used. Starters with a Bendix type of starter drive, will typically use a remote starter relay to actuate the starter. This is because the starter drive will extend automatically with the rotation of the starter. It uses centrifugal force to extend the drive and the drive is retracted by the spinning motion of the flywheel after the engine starts. Starters that use a mounted or integral solenoid use the solenoid to mechanically extend the starter drive and close the circuit that supplies current to the starter. The starter drive used on this system is an overrunning clutch type drive. This type of drive spins free in one direction and locks in the other. This action allows the starter drive to spin the flywheel, when engaged, and spin free when the engine starts. The starter drive is withdrawn when the ignition key is returned to the run position.