The rotor is an electromagnet that rotates freely in the alternator. It consists of a coil of wire wound on an iron core, and pressed on a steel shaft. An iron segment is fastened on each side of the coil assembly so that the projections or claws interlace. The ends of the rotor coil are connected to insulated slip rings mounted on the shaft and spring loaded brushes maintain contact with the slip rings at all times.
When a current is passed through the slip rings and the coil winding, it establishes a north and south pole at the ends of the iron core and the shaft. The projections then take on the same polarity as the end of the shaft on which they are mounted and this forms pairs of north and south poles around the rotor circumference.
The rotor usually has 8 to 12 poles, which are tapered to reduce noise as the rotor rotates.