Editing Motor controller (section)

== Applications ==
Motor controllers are used with both [[DC motor]]s (direct current) and [[AC motor]]s (alternating current).  A controller includes means to connect the motor's windings to the electrical power supply, and may also include overload, over-current, and oveheating protection and wiring (i.e. [[magnetic starter]]). A motor controller may also supervise the motor's field circuit, or detect conditions such as low supply voltage, incorrect polarity or incorrect phase sequence, or high motor temperature.  Some motor controllers limit the inrush starting current, allowing the motor to accelerate itself and connected mechanical load more slowly than a direct connection. Motor controllers may be manual, requiring an operator to sequence a starting switch through steps to accelerate the load, or may be fully automatic, using internal timers or current sensors to accelerate the motor.

Some types of motor controllers also allow adjustment of the speed of the electric motor. For direct-current motors, the controller may adjust the voltage applied to the motor, or adjust the current flowing in the motor's field winding. Alternating current motors may have little or no speed response to adjusting terminal voltage, so controllers for alternating current instead adjust rotor circuit resistance (for wound rotor motors) or change the frequency of the AC applied to the motor for speed control using power electronic devices or electromechanical frequency changers.

The physical design and packaging of motor controllers is about as varied as that of electric motors themselves. A wall-mounted toggle switch with suitable ratings may be all that is needed for a household ventilation fan. Power tools and household appliances may have a trigger switch that only turns the motor on and off. Industrial motors may be more complex controllers connected to automation systems; a factory may have a large number of motor controllers grouped in a [[motor control center]]. Controllers for electric travelling cranes or electric vehicles may be mounted on the mobile equipment. The largest motor controllers are used with the pumping motors of [[pumped storage]] hydroelectric plants, and may carry ratings of tens of thousands of horsepower (kilowatts).<ref>Terrell Croft, Wilford Summers, ''American Electricians Handbook Eleventh Edition'', McGraw Hill, 1987, ISBN 0-07-013932-6, pp. 7-119 through 7-189</ref>