On Sunday 04 August 2019 10:45:08 John Hasler wrote: > 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.
And that plays hob with the power factor. But with 6 houses on that can, and no one else with machinery, pure residential loads, I don't figure my 2 vfd's are going to be noticed. The 2nd one is a 127 volt input, driving a 1.5 horse water cooled spindle on a 6040 gantry style mill, can do 24k rpms at full 400 hz song. And actually, I have a dc motor supply I have to softstart, too many u-f's in the filter bank, a hard start trips a 30A (and definitely sick bird breaker). The softstart lets me use a just barely legal 20A breaker. Normal draw is under 4 amps when the machine is working unless its rigid tapping with a big tap. But this is a long ways offtopic, so last post. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene>
