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Re: 3 phase power converters

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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>

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3 phase power converters (was: Re: 3 phase power (was Re: Wireless home LAN - WiFi vs Bluetooth?)) rhkramer@gmail.com - 2019-08-04 03:40 +0200
  Re: 3 phase power converters John Hasler <jhasler@newsguy.com> - 2019-08-04 05:40 +0200
    Re: 3 phase power converters Gene Heskett <gheskett@shentel.net> - 2019-08-04 06:20 +0200
      Re: 3 phase power converters John Hasler <jhasler@newsguy.com> - 2019-08-04 16:50 +0200
        Re: 3 phase power converters Gene Heskett <gheskett@shentel.net> - 2019-08-04 18:00 +0200

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