The alternator, also known as generator, Dynamo, or current generator, supplies the energy power needed by all electric components in a motor vehicle, and also charges the battery. It acts as a buffer storage and an energy storage device for the equalization of different current voltages. This way, the electricity can be used even when the engine is turned off. If one has left the light on in the car by mistake, it may happen that the battery goes flat. If the engine, nevertheless, starts, it is important to drive several kilometres‘ distance, before parking the car again, so that the alternator may recharge the battery. In the early years of car manufacturing, the alternator merely powered the headlights, because, back then, no other electric components were installed in motor vehicles. Nowadays, important elements such as indicator lamps, radio, electric windows, or modern on-board computers, must be additionally supplied with electricity, which means that the alternator has to deliver an even higher performance.
The alternator is usually powered by the engine as auxiliary unit by means of a V-belt and in this way it transforms mechanical energy into electrical energy. The alternator functions thanks to electromagnetic induction: thus, through the movement of an electric conductor (the alternator rotor) in the magnetic field, electric tension is generated. With the aid of a regulator, the latter is normally set at a 12 Volt voltage, to avoid the possibility that the voltage should vary wildly with different engine speeds. When more electricity than needed is generated, the alternator uses the excess to charge the battery. In the automobile industry there are three distinct types of alternators: the direct current alternator, the alternating current alternator, and the three-phase alternator, which has prevailed since the 1970s in the motor vehicle construction business.