Winches come with one of two major types of motors: permanent magnet motors or series wound motors. All winch motors have a set of coils inside them called an armature. Inside this armature is either another set of field coils or a set of permanent magnets. Permanent magnet motors use magnets to rotate the armature and run the engine. Permanent magnet motors cause very little strain on the car battery, but they overheat easily, which causes the motor to slow down; therefore they can't be used for very heavy winching jobs. Series wound motors have another set of coils inside the armature, called the field coils. These field coils are connected to the armature and cause it to spin. When the field coils spin, the magnetic field is created gradually, and the armature spins. Because of this extra effort, series wound motors use more current than permanent magnet motors. But they do not heat up as easily as permanent magnet motors.