The basic principle on which a DC motor works is that whenever there is a current carrying conductor placed inside a magnetic field, the conductor will experience a mechanical force. Since all DC motors work on the basis of this principle, it is necessary to have a magnetic field. The permanent magnet electric DC motor is very simple to construct and is usually used as a starter motor. You will find them in battery operated toys, blowers in heaters, windshield wipers, washers, power windows etc.
The main difference caused when you used a permanent magnet instead of an electromagnet is the lack of external control of the magnetic field strength. This is because the permanent magnet’s field strength is fixed, allowing for no variations. Due to this, there cannot be field control of the electric DC motor. So, these permanent magnet DC motors are used in applications where speed control, by controlling the field, is not required.
Teco Electric Co. Ltd. manufacture these motors which can be used for both household and industrial purposes. Nowadays, permanent magnets are used in small sub fractional and fractional kilo watt motors.