At 11:13 PM 3/27/2012, RussellMc wrote: >http://cache.freescale.com/files/microcontrollers/doc/app_note/AN3471.pdf > >If single phase motors can be speed controlled this was then people >would do it in droves. >I have severe doubts about this circuit. > >But, Freescale must be right. No? Yep. Large industrial ceiling fans installed in warehouses normally come=20 with a speed control which is nothing more than a lamp dimmer that is=20 optimized for inductive loads. The speed pot is also wired backwards=20 - when you rotate it clockwise from the OFF position, the speed is at=20 maximum. That's an attempt to ensure that fan actually begins to rotate. What they are doing is entirely reasonable if you think of the motor=20 as having just enough torque to spin the fan at its maximum safe=20 speed. Chopping the waveform reduces the torque, which then reduces the sp= eed. This technique does NOT work for motors that either are much larger=20 than the torque load or for motors that have varying mechanical=20 loads. Ceiling fans just happen to be the correct combination of=20 limited motor torque and proportional load as the speed is varied. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .