A.C. motor control - motor control for squirrel cage motors

7-54 - elektor july/august 1982 This circuit makes it possible to control the speed of single phase motors with squirrel cage. This is not to say that every motor can now be made to run at any desired speed, but, that a speed range to a factor of 2 should be readily obtainable with suitable motors. That is to say that the range is from half to full speed. This range may not seem to be much, but, for fans, pumps and other equipment of this nature, it is quite a useful range. It can conveniently reduce both the current consumption, and noise levels of this type of appliance. The circuit described here makes use of an SGS Ates IC that was specifi- cally designed for phase control. An asynchronous (short circuit rotor) motor has two windings, their mag- netic fields being at 900 to each other. One winding is connected directly to the mains, the other via a capacitor to ensure that the current passing through one winding is out of phase to the other. This invariably results in a rota...