Re: 3 phase power converters
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
--
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