On Fri, Apr 27, 2012 at 6:06 PM, Robert Rolf wrot= e: > What do you have for AC supply now? > If you have a center tapped transformer, and only want two speeds, > use a relay to switch between using the full output, and half of it. The unit is powered by an AC wall wart. > Phase control is phase control A fan dimmer will work at 18VAC. > You just won't get the full range of control. You won't get to 100% outpu= t > because the R/C for the diac is too long at low supply voltage. > If that is a problem (80% max) you can fix that by reducing > the value of the C disharging into the diac to fire the triac (since you'= d > have a harder > time replacing the pot with 1/5 the value). > > The alternative is to put the fan dimmer on the input to the transformer > that is > currently supplying the motor, but most dimmers can't handle the inductan= ce > of an unloaded transformer very well. The usual issue is lack of holding > current > at low values of output, which you can 'fake out' by using a 3W christmas > light bulb or equivalent. This also gives you a motor power level > indication. What would happen if I tried the old "reduce your soldering iron temp" trick and put a diode in line? I'd be cutting off one half of the AC cycle, but I get the feeling this won't work quite as well as I'm hoping... Josh --=20 A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. =A0 =A0 =A0 =A0 -Douglas Adams --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .