AC generator. Computer illustration showing the structure of a typical AC generator. AC generators (or alternators) produce electricity by converting motion into alternating current (AC), which means the voltage produced alternately reverses from positive to negative polarity. AC is generated by rotating a magnetic field within a stationary wire coil, or by rotating a coil within a magnetic field, as shown here. The main components of an AC generator are: the coils (1- 4), the magnets (5 -6), the slip rings (7-8) and the brushes (9-10).