An alternator is part of the charging system of your car that produces electricity for many devices. A type of generator, the alternator transforms mechanical energy into electrical energy. Although your car's battery supplies some electricity, most of the electrical mechanisms within the vehicle, require the alternator's steady stream of power.

Alternating current (rather than direct current) gives the alternator its name, because this is the type of electricity it creates. It's mainly a mechanical device, concealing a pulley, wheels, brushes and wires, which hooks to the crankshaft and runs to the battery. This way, the gasoline powers the engine to turn the crankshaft, which in turn connects to the alternator. The alternator converts that motion into current whenever the car is running. The resulting electricity operates the cooling fan, headlights, windshield wipers, radio, defogger, and air conditioning.

To be more specific, an alternator is very efficient at producing a constant, high voltage, even when the car is idle, because of how it works. The belt (from the crankshaft) connects to a pulley system, called the rotor, such that when the belt is turning, it moves magnets across a special surface, called a conductor. Moving magnets, in the stator, generate an electrostatic field, otherwise known as electricity. This alternating current is controlled by a voltage regulator to keep the voltage steady. Another part, called the diodes, convert alternating current into direct current that flows on to the battery and other components.

Even if your alternator dies or malfunctions, your car will run for a while directly off of the battery, until all the battery's power is sapped. Therefore, it is hard to tell when your alternator has problems. Sometimes a harsh noise, or intermittent headlights, will give it away. Check to make sure the belts on the alternator are not cracked, or improperly tightened, before you replace the entire thing. A rebuilt alternator can be a reliable, but less expensive, option if you need it repaired.