There are two basic types of motors to run with alternating current and they are the synchronous motors and the induction motors. The synchronous motor is basically a three-phase alternator that works cogged v belt in reverse and the field magnets are mounted on a rotor and excited by direct current, and the coils of the armature are divided into three parts and fed with three-phase alternating current. The variation of the three current waves in the armature generates a variable magnetic reaction with the poles of the field magnets, and causes the field to rotate at a constant speed, which is motivated by the frequency of the current in the alternating current power line.
The stable speed of a synchronous motor is advantageous in certain devices, however, this type of motor can not be used in applications where the mechanical load on the motor becomes very high, since if the motor slows down when it is low load can be out of phase with the frequency of the current and come to a standstill. Synchronous motors can work with a single-phase power source by including the appropriate circuit elements to achieve a rotational magnetic field.