What Are the Parts of a Starter Solenoid?


Quick Answer

A starter solenoid consists of a small switch, an electromagnet and an iron rod attached to a spring. The switch turns on an electromagnet very quickly, attracting the iron rod that completes an electric circuit, starting the ignition process.

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Full Answer

The starter solenoid is designed to provide just enough electrical power to start a vehicle's engine without producing dangerous sparks. Since the vehicle starter needs a heavy electric current to operate, the solenoid operates where a hand-operated switch works if such a heavy load is not needed.

Upon turning the key in the ignition switch, current travels to the solenoid. The ignition process begins with the current feeding an electromagnet that attracts an iron rod, completing an electric circuit that delivers power to the rest of the starter assembly and then quickly draws back the iron rod by a spring. This short contact is what protects the assembly from overloading and creating dangerous conditions that can lead to fire.

Even if safeguards against fire are put into place, the starting process uses a great deal of electricity and runs the vehicle's battery down quickly if the contact is any longer than strictly necessary. Typically, the solenoid's pinion has a one-way clutch incorporated, preventing the engine from transferring power to the solenoid and attempting to drive the starter motor at high RPM.

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