Find out what's inside a car alternator and just how it works!

The alternator on a car is responsible for taking mechanical energy from the engine and turning it into electrical energy to replenish the battery. It is powered by the crank shaft, through the serpentine belt.

Inside, the pulley rotates a rotor, which is an electromagnet. When powered, the electromagnet spins relative to stationary coils on the housing, called the stator.

Through the right hand rule of physics, we know that as a magnet passes a coil, a current is induced. In this case, there are three separate stator windings, phased 120 degrees apart.

The rotor's electromagnet is often a Salient pole electromagnet, in that each finger alternates pole, from north, to south, to north, etc. When the changing field passes the stator coils, it generates an alternating current.

The three-phase, 120 degree, alternating current produced in the stator coils cannot charge the battery. It is then sent through a rectifier to be converted to direct current, through the use of a bridge rectifier (diodes) and a capacitor as a filter.

Since the engine's RPM varies, so will the alternator's output. However the battery needs a constant 14V to keep charged. The voltage output is controlled through the voltage regulator. It is a solid state device that will sense how charged the battery is, and then send more or less current to the rotor windings. Less current to the electromagnet rotor means less current generated in the stator, and the battery won't get overcharged.

In this video, an alternator is removed and completely disassembled from a 2001 Toyota Corolla.

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