Thanks, Dwayne. Not only is this simlpe and inexpensive, but it lets me use
some h/w & code from recent projects to modernize the basic idea. I remember
fixing bench-top machines that formed axial component leads with this type
of driver back in the 70's. It may not be as efficient as PWM driving via
FET's, but I can see how it would be clean and simple. For this little
laminating machine it should be fine.
Now for the catch - current limiting - at AC freq it's always fun getting a
good running current averaging circuit with impedance a PIC ADC will
handle.....
But then again, I did ask for a starting point.......

Chris
>
> If this is something like a treadmill motor, all you should
> need is a phase
> controlled full wave bridge rectifier (2 diodes, 2 SCRs)
> operated directly
> from the 120 Vac line.  This is how most tread mills do their
> speed control.
>
> The 90V rating on the motor comes from full wave rectifying
> the incoming
> 120 Vac but not filtering it; and operating a somewhat less
> than the full
> 180 degree conduction for each half-cycle.  Most older
> blueprint machines
> use similar motors (smaller, of course) and control techniques.
>
> For a simple test, just grab a fan-motor rated speed control
> and connect it
> to a bridge rectifier feeding the motor.  Should work just fine.
>
> dwayne
>
> --
> Dwayne Reid   <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> (780) 489-3199 voice          (780) 487-6397 fax
>
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