Permanent-magnet types have some performance advantages over direct-current, excited, synchronous types, and have become predominant in fractional horsepower applications like short duty applications. They are smaller, lighter, more efficient and reliable than others. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field for large industrial DC Motors.
DC motors were the first type widely used since they could be powered from existing direct-current lighting power distribution systems A DC motor's speed can be controlled over a wide range, using either a variable supply voltage or by changing the strength of current in its field windings. Small DC motors are used in tools, toys, and appliances. The universal motor can operate on direct current but is a lightweight motor used for portable power tools and appliances.
A coil of wire with a current running through it generates an electromagnetic field aligned with the center of the coil. The direction and magnitude of the magnetic field produced by the colt can be changed with the direction and magnitude of the current flowing through it.
A simple DC motor has a stationary set of magnets in the stator and an armature with one or more windings of insulated wire wrapped around a soft iron core that concentrates the magnetic field. The windings usually have multiple turns around the core, and in large motors there can be several parallel current paths. The ends of the wire winding are connected to a commentator. The commentator allows each armature coil to be energized in turn and connects the rotating coils with the external power supply through brushes.