Cars Simplified


A vital part of any vehicle's electrical system, the alternator generates electricity for both the engine's ignition system and the vehicle's entire electrical system. Some of the engine's power is used to turn a set of electromagnets in the alternator, which, when passed by the wires inside the alternator, generates electricity. The amount of electricity made depends on the engine's speed and the size of both pulleys involved (the crankshaft pulley and alternator pulley).

Prior to the 1960s, automobiles used direct current generators with commutators. When diodes that were durable enough for underhood conditions became priced reasonably enough to use, automotive manufacturers switched to using alternators. Chrysler was the first to mass-produce a vehicle with an alternator (the 1960 Chrysler Valiant), and the Ford Model T was the first car to experiment with the use of an alternator.

A used GM/AC Delco Alternator

Parts of an Alternator

Although the alternator itself is considered a part, there are many parts within an alternator.

Outer Shell

The outer shell of an alternator is usually made up of two aluminum housing pieces with vent openings to allow cooling. The two pieces are called the drive-end shield and collector ring end shield. Many alternators have an additional protective cap for the electronic components outside the metal casings.


The engine sends its rotational energy to the alternator via a belt to the alternator's pulley. The diameter of the pulley affects the speed that the alternator rotor spins, relative to engine speed; a smaller pulley allows the rotor to spin faster than a large pulley would.


The stator is a solid piece which stays stationary within the alternator. It has copper windings which direct the flow of electricity.


The rotor spins within the alternator, interfering with magnetic fields in order to produce alternating current. The rotor is attached directly to the pulley, and rides on at least two roller bearings.

Alternator Rotor


The rectifier contains the diodes and any other electronic components the manufacturer chooses to add. Most rectifiers are contained within a plastic cap outside of the metal shell, and have a heat sink to cool off the heat-producing electronic components.