For the most part, alternators are relatively small and lightweight. Roughly the size of a coconut, the alternators found in most passenger cars and light trucks are constructed using an aluminum outer housing, as the lightweight metal does not magnetize. This is important since aluminum dissipates the tremendous heat generated by producing the electrical power and since the rotor assembly produces a magnetic field.

If you closely inspect an alternator, you'll find it has vents on both the front and back side. Again, this aids in heat dissipation. A drive pulley is attached to the rotor shaft on the front of the alternator. When the engine is running, the crankshaft turns the drive belt, which in turn spins the pulley on the rotor shaft. In essence, the alternator transfers the mechanical energy from the engine into electrical power for the car's accessories.

Alternators are used in automobiles to charge the battery and to power all the car's electric systems when its engine is running. Alternators have the great advantage over direct-current generators of not using a commutator, which makes them simpler, lighter, and more rugged than a dc generator. The stronger construction of alternators allows them to turn at higher speed, allowing an automotive alternator to turn at twice engine speed, improving output when the engine is idling. The availability of low-cost solid-state diodes from about 1960 allowed auto manufacturers to substitute alternators for generators. Automotive alternators use a set of rectifiers (diode bridge) to convert ac to dc. To provide direct current with low ripple, automotive alternators have a three-phase winding.

Modern car alternators also have a voltage regulator built into them. Typical car alternators generate the field using a dc current through slip rings. The field current is much smaller than the output current taken from the fixed stator windings, and so heavy duty slip rings are not required. For example, in an alternator rated to produce 70 amperes of dc, the field current will be less than 2 amperes. The voltage regulator operates by modulating the small field current in order to produce a constant voltage at the stator output.

Basic components of alternator

* a stationary winding assembly, called the stator.

* a rotating electro-magnet, the rotor.

* a slip-ring and brush assembly.

* a rectifier assembly.

* 2 end-frames.

* and a cooling fan.