Gene writes: > Three phase, at most any frequency can be had a lot cheaper at up to > 10 horse or so by using a suitably sized VFD.
Yes. Don't buy a static or rotary converter for a single machine. They only make sense these days if you can build them at no cost with stuff you have laying around. Put an external fan on your motor. If you are going to operate at those frequencies a thermistor in the windings would also be a good idea. The motor is very inefficient down there so you want to keep an eye on the temperature even with forced cooling. The thermistor can also control the fan. You can get more torque at high frequencies if you up the voltage, but most VFDs can't do that. Besides, you'd be pushing the voltage rating on the insulation. One reason to consider a motor-generator set (or utility supplied three phase) for a shop full of VFD-equipped three-phase machines is that VFDs operating from single phase are limited by the need for large filter capacitors. -- John Hasler [email protected] Elmwood, WI USA
