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3 phase power converters (was: Re: 3 phase power (was Re: Wireless home LAN - WiFi vs Bluetooth?))

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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

#212217 — 3 phase power converters (was: Re: 3 phase power (was Re: Wireless home LAN - WiFi vs Bluetooth?))

Just wanted to mention for anyone that might need 3 phase power in a home 
environment, there are ways to convert 120/240 "single phase" power to, for 
example, 208 or 480 volt 3 phase power if you have a need and don't require 
too much horsepower, and at a cost of much less than the $20,000 that someone 
mentioned as the cost to get it installed by a power company.

One is a motor / generator set, with a 240/120 volt single phase motor driving 
a 3 phase generator at, for example, 208 or 480 volts.

Another is a static device known as an "add-a-phase".

In the case of the motor / generator set, in most cases you won't achieve 60 
Hz., but instead something less than that, but, even machine tools with 
gearing (or electronics) to do things like match a feed rate to a rotation 
rate (to cut threads) should be able to handle that (mechanical gears will 
maintain the proper ratio) or be modified to handle that (I would expect that 
an electric feed device either already has the components to detect the main 
motor speed and adjust the feed rate or be able to be modified to do so.

There is a limit to how big a machine(s) you can handle this way -- if you can 
provide say a 40 amp feed from a 240 volt single phase circuit, that is about 
10 kw and maybe 13 Hp.  -- a motor generator set with a 13 Hp. motor  should 
be able to drive a generator to handle something like a 10 Hp. 3 phase motor 
(or more, depending on the efficiencies and the required starting current).



On Thursday, August 01, 2019 05:33:08 PM rhkramer@gmail.com wrote:

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#212218 — Re: 3 phase power converters

A static converter doesn't produce three phase.  It converts a
three-phase motor into a capacitor start, capacitor run single phase
motor by connecting two of the phases to the single phase lines and
connecting the third phase to one of the lines through capacitors.  It
only works for motors and needs to be tuned for a specific motor.

A real motor generator set *will* produce 60 Hz three phase because the
motor and generator will be synchronous.  The power will also be
seperately derived (not connected in any way to the single phase).

More comon than real motor-generator sets are "rotary converters".
These are large three phase motors wired up like the static converter
discussed above but with slightly different capacitor values and not
connected to any mechanical load.  Three phase loads are then connected
to the phases of the motor.  This produces a fair approximation of three
phase but note that two of the phases are connected to the single phase
lines.  This means that you have neither a neutral nor a grounded
conductor (unless you are in Europe in which case you have
corner-grounded delta).
-- 
John Hasler 
jhasler@newsguy.com
Elmwood, WI USA

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#212219 — Re: 3 phase power converters

On Saturday 03 August 2019 23:30:47 John Hasler wrote:

> A static converter doesn't produce three phase.  It converts a
> three-phase motor into a capacitor start, capacitor run single phase
> motor by connecting two of the phases to the single phase lines and
> connecting the third phase to one of the lines through capacitors.  It
> only works for motors and needs to be tuned for a specific motor.
>
> A real motor generator set *will* produce 60 Hz three phase because
> the motor and generator will be synchronous.  The power will also be
> seperately derived (not connected in any way to the single phase).
>
> More comon than real motor-generator sets are "rotary converters".
> These are large three phase motors wired up like the static converter
> discussed above but with slightly different capacitor values and not
> connected to any mechanical load.  Three phase loads are then
> connected to the phases of the motor.  This produces a fair
> approximation of three phase but note that two of the phases are
> connected to the single phase lines.  This means that you have neither
> a neutral nor a grounded conductor (unless you are in Europe in which
> case you have
> corner-grounded delta).

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. I'm useing 2 1.5 horse rated, 
to drive a 1 horse 3 phase motor, currently available from ebay for 
about a hundred bucks. Top frequency is 400 hz, but motor inductance 
reduces the drive currant to under an amp a phase at around 200 hz, so 
theres little torque to do work above 150 hz.  But I can get turn the 
house around torque at 5 hz, not forever because the  motors fan does 
not move cooling air when its not running at normal speed. But for a 20 
minute job its fine. Lathe itself has an 8 speed drive, rarely changed 
out of 5th, the vfd does it all.

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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#212238 — Re: 3 phase power converters

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 
jhasler@newsguy.com
Elmwood, WI USA

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#212242 — 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
-- 
"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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