AC generators (Figure 19-2)use a design that is basically the reverse of a DC generator . In an AC generator (Figure 19-3), a spinning magnetic field (called the rotor) rotates inside an assembly of stationary conductors(called the stator). As the spinning north and south poles of the magnetic field pass the conductors, they induce a voltage that first flows in one direction and then in the opposite direction (AC voltage). Because automobiles use DC voltage, the AC must be changed or rectified into DC. This is done through an arrangement of diodes that are placed between the output of the windings and the output of the AC generator.