Unlike induction motors, polyphase synchronous motors need a synchronous motor starter to start and maintain a constant synchronous speed. A synchronous motor starter supplies an AC voltage through a contactor usually in a combination starter or controller to the stator. A solid state field application panel in the starter supplies rotating dc field coils mounted on the rotor with a dc voltage. When the synchronous motor is nearly up to speed, the field application panel energizes the rotating fields and turns them into magnets so the magnet poles lock with the poles of the stators’ rotating magnetic field and thus the motor rotates at synchronous speed.