An alternator is a device that converts mechanical energy into electrical energy, primarily used in vehicles. It generates alternating current (AC) electricity, which is then converted to direct current (DC) to charge the car battery and power the electrical systems when the engine is running. Alternators work by using a rotating magnetic field and coils of wire. As the engine turns the alternator's rotor, it creates a magnetic field that induces an electric current in the stator windings. This process ensures that the vehicle's electrical needs are met while keeping the battery charged.