"It all depends..."  on what type of AC motor you are trying to
control.  If it is an induction motor or shaded pole motor, that could
get difficult and expensive.  However if it is a small "series wound"
motor then it is much more simple.  A series wound motor is the type
found in many small appliances.  It is also found in vacuum cleaners,
electric drills, Dremel tool, Skil saws, routers and so forth.  It is
characterized by having brushes to connect the armature (rotating
part).

In theory also, a series wound motor, in the absence of wind resistance
to the rotating parts, bearing friction and load, will spin to infinite
RPM.  So it usually is found in applications requiring high starting
torque and may or may not be geared down.  Ah, un-fond memories of
"Rotating Machinery 101" (but I noticed that course is no longer on the
curriculum!)

A series wound motor can easily be controlled by a "light dimmer" as
long as it doesn't draw more power than the typical dimmer module will
handle, typically 600 watts.  You wire it up the same way as a light
dimmer circuit on a light bulb, just replacing the motor for the light
bulb.

Harvey Chao
harveytchao@earthlink.net.geentroep [delete ".geentroep" to reply]