An alternator is a generator that produces alternating current by converting mechanical energy to electrical energy.

Alternators are generally simpler, more reliable, and can be more efficient than direct current generators because they do not need to use brushes and commutator/slip rings.

Alternators generate electricity by the same principle as DC generators. When magnetic field lines cut across a conductor, a current is induced in the conductor.

In general, an alternator has a stationary part (stator) and a rotating part (rotor). The stator contains windings of conductors and the rotor contains a moving magnetic field. The field cuts across the conductors, generating an electrical current, as the mechanical input causes the rotor to turn. The field may be induced (as is in induction motors) or in the form of permanent magnets. Permanent magnet alternators have the potential to be the most efficient since no mechanical energy is used to create the field.