On Wed, 29 Oct 2003 06:30:18 GMT, "DeepDiver"
wrote something
.......and in reply I say!:

"william_b_noble" wrote in message
...

ok, you asked. these are triac based controls that duty cycle modulate
the input AC power - basically they delay the turn on of the AC to the
motor until a desired phase angle is reached - the later the turn on
(each half cycle) the less power is delivered to the motor.

That sounds like PWM. Is that what these controllers are?


Sort of similar, but use the sine wave. Imagine a sine wave. then
switch it on at a certain time within each half cycle, and only to be
turned off at the end of that half cycle (a triac is fired by a
trigger pulse of very short duration, and will turn off only when the
_supply_ voltage reaches zero again). The earlier you turn it on in
the half cycle, the more power gets to the driven motor etc.

Check out Thyristor. A Triac is two thyristors back to back and
reversed, to control AC in both directions of current flow.


It is my understanding that a PWM drive will offer max torque over the speed
control range because the motor always sees peak voltage (but that the
voltage is chopped so that the average current determines the speed).

I doubt it. Torque is pretty much tied in with applied average power,
all other factors being equal. Shorten the pulse, lower the power. To
obtain max or constant speed, you need to usually measure either the
speed of the motor, or the back EMF from it, or current draw for
applied voltage, and provide more or less power as needed in each
pulse.

To make the triac parallel, you will see a loss of torque and power as
soon as you start to delay the firing of the triac, even though the
currtent still passes through peak until you reach a quarter cycle.


I am trying to build a power table feed for a mini mill. I've got a
high-torque 24VDC gear motor, but I'm still looking for an electronic
circuit to drive it. I know some people have used a light dimmer with the
output routed through a step-down transformer; perhaps a more version would
use one of these universal motor speed controllers in place of the light
dimmer.

Anyone have suggestions for either an economical off-the-shelf solution, or
a schematic for a basic PWM circuit?

Not being smart. Try googling PWM circuits. To get a constant torque
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