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Re: AC Motor Speed Control

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Posted by Dianne/">Dianne on February 28, 2000 12:33:14 UTC

: I would like to control the speed of a 1750rpm washing machine motor im using in a home-made grinding machine : electronically(an scr circuit perhaps)as it is now, im using a 1" pully on the motor,and a 14" on the spindle,which : turns at about 170rpm,would like to vary the rpm,without using a system of pully's,from 0 to 100rpm,anyone know : where i could locate an ac motor controller,or schematic for one? : Thanks : stevec.

Those motors don't like speed controllers! Because they do not have a wound-armature, they work by the field inducting a current into the armature, which has the equivilent of a "shorted turn" which generates a magnetic field opposing the field coils and the "repulsion" gives you the driving force.

Almost all speed controls work by chopping the input voltage, thereby lowering the voltage going to the motor. With a fractional-horsepower (washing machine) motor, it still wants to turn at the same speed (since that's a factor of the phase angle of this induced armature field), but now it has to do it with less voltage, which means more current, which means lots of heat.

Find a motor with a wound armature - it will work much, much better for variable speed.

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