What is the operating principle of ceiling fan speed control?
Explanation with curves In the operation of an AC motor, the frequency of the applied power determines the motor’s speed and the voltage determines the motor’s torque capability. The torque capability is actually defined by a curve showing torque capability vs. operating speed. Motors are usually selected for loads such that the load torque requirement curve is below the motor’s torque capability curve. The load curve crosses the motor curve at a point near the motor’s maximum speed. When the motor is started, it will accelerate the load until it is operating at the speed corresponding to the intersection of the motor and load curves. See: http://i1.tinypic.com/6peb3mx.jpg Some motors, such as shaded pole motors, have a torque capability curve that allows the motor speed to be controlled by reducing the applied voltage. This technique works best when the load torque requirement rises as speed increases. See the image linked
