This does work. I have applied a similar circuit, replacing the control potentiometer with a PWM output generated by a PIC. The speed is monitored and tracks a digital setpoint on a display. This is a power controller, not a 'speed' control as such, and the power is reduced by phase shifting the triac firing point in relation to the zero crossing point until the synchronous motor cannot hold lock and starts skipping. This produces a humming sound and excess heat, which becomes progressively more pronounced as speed is further reduced. Crude indeed, but acceptable if the control range required is sufficiently limited. The only 'proper' way to vary the speed of a synchronous motor is with a VF= D On Wed, Oct 3, 2012 at 5:57 AM, IVP wrote: > > It is worth a try, it may work well enough within the range you need > > Thanks > > > But keep watch of the motor temperature, you probably will not be > > able to get anywhere near continuous use without overheating > > Yes, although the motor has a fan blade on its shaft I do have forced > cooling planned > > Another option I may try is to copy what my lathe, drill press and > bandsaw do, and that's have pulley 'gear boxes'. So for example I > can reduce blade speed without changing the motor speed, with the > option of motor speed control too. eg 1:5 gearbox reduction and > only 1:2 motor speed reduction -> 1:10 overall. But all that entails > rebuilding the scrollsaw, which is probably OTT > > Joe > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Perry Curling-Hope Research and Development --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .