Saturable Reactors as Ballast Discussion
Updated: 07-29-06
Date: Wed, 21 Dec 2005 15:05:03 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Saturable Reactors as Ballast
Original poster: "Carl Litton" <Carl_Litton@hilton.com>
Does anyone on this list have any experience building saturable reactors for
ballasting purposes? I found some older notes in the archive suggesting that a
second winding on an iron core inductor can be used to introduce a variable DC
voltage that will give full range control of the inductance as the core
approaches saturation.
I have been able to demonstrate the effect on a small scale with a simple step
down transformer by putting the primary in series with a 120 VAC ciruit and
connecting the the secondary to the rectified out put of a Variac. A 2.7 Henry
inductor was reduced to a little less than 1 Henry with 140 VDC in the control
winding, allowing a small light bulb just enough current to give off some
visible light (measured current 0.188 Amp with no DC control and no light to
0.42 Amp with 140VDC control and visible soft glow from bulb).
However, all attempts to do this on any large (20 to 250 lbs.) inductors
controlling a 240 volt circuit in the 30 to 150 Amp range have been not only
fruitless but have almost instantly slagged the 25 Amp bridge rectifier
connected to the control winding.
I need to understand what I am missing here. Any theory or especially winding
diagrams of working reactors would be greatly appreciated. I did find one
article that suggested 2 AC power windings in series and in phase have to be
used with 2 DC windings in series and "out of phase" with each other in order to
cancel the effect of induced AC in the control winding. But here again, no
practical application, turns ratios, winding configurations, etc.
Any thoughts? Thank you, Carl Litton, Memphis HV Group
Date: Wed, 21 Dec 2005 17:28:27 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: "Mike"
<induction@comcast.net>
Hi Carl,
About the PRS (Primary Saturable Reactor) control systems, we use that often at
work with induction heaters.
Three usual modes of power level control are used, SCR, Thyratron and PSR. On
the PSR's three ways to effect control, one is a mag amp that takes pot input or
instrument input (pyrometers, etc), the other is a simple SCR zero to ~ 90
volts, up to 25 amps available to control windings. Both of the prior are 115
volt input, 0 tom 90 VDC out. The third and less costly is simple variac and
rectifier as you said. For three phase, there is one saturable reactor per leg
going to the plate transformer primary. While the three PSR's are isolated
phase to phase, the DC control loop is in series with each DC winding of the 3
PSR's. Also, each usually has a 100 Ohm resistor across both ends of each DC or
control winding to equalize. Typical current for a 10 through 50 kW machine,
through all 3 control windings, is in the area of 4 to 5 amps. The greater
current, the more "pass through". Most PSR control systems limit voltage to 90
volts figuring a group of 3 reactors will be in the loop. Expect a ~ 10 volt
drop so set the XMFR taps one step below your line voltage. It is important
that you understand a few things about PSR control, first, the things are very
load dependant. The plate transformer may
park at minimum of ~5 to 10 percent power, even when the control is saying
minimum power, with the oscillator tube as the minimum load, so PSR.s rarely go
all the way off. Also, they are a tad slow, it may take 2 or 3 seconds to
flatten out where you set the power control pot. Fine for long term jobs but if
somebody is looking for on, heat, off cycles in a .5 or 1 second window, this is
not the control system to use but rather SCR or thyratrons. If you remove the
minimum load, where the plate kV meter may say 1000 volts, the plate transformer
will go right up to full voltage. If I have a Tech Support call saying HV
overloads, I have them remove the Osc tube filament connection so the tube won't
conduct. Any current reading past that is Cap leakage, or other items like
blocker caps, etc. As soon as the Fil;ament is off the tube, the voltage goes
pretty much all the way up so it's a self contained hipot. The inductance, the
transformer impedance, the load current range minimum to maximum, need to be
known to get the right swing of minimum to maximum control and stay within the
control range of the pot for linearity. About the windings, most of the ones we
use in rebuilding machines have a Burndey connector jumper setup so we can set
240 or 480 volt range per leg.
This leaves two wires, one per leg in, one to transformer, out. The two small
wires go to the DC control loop and the equalizing 100 ohm resistor across each
DC winding. The input is of course on a contactor, the output connects to each
plate transformer input. So, you need to know expected load current swings at
least to get a
PSR in the right area, else you will not have good control on it. You can often
get these in the KVA range you are working at by finding an old tube induction
heater with PSR in it. Some even had an outside, roll around PSR mini frame you
could connect to the machine. Auctions, Ebay, you name it. Decent PSR's are
about 1800 Bux each, not cheap. Slow but very smooth control, also helps wash
out line spikes from getting your diode stacks. Hope this helps.
Mike
----- Original Message ----- From: "Tesla list" <tesla@pupman.com>
To: <tesla@pupman.com>
Sent: Wednesday, December 21, 2005 5:05 PM
Subject: Saturable Reactors as Ballast
>Original poster: "Carl Litton" <Carl_Litton@hilton.com>
>
>Does anyone on this list have any experience
building saturable
>reactors for ballasting purposes? I found some
older notes in the
>archive suggesting that a second winding on an
iron core inductor
>can be used to introduce a variable DC voltage
that will give full
>range control of the inductance as the core
approaches saturation.
>
>I have been able to demonstrate the effect on a
small scale with a
>simple step down transformer by putting the
primary in series with a
>120 VAC ciruit and connecting the the secondary
to the rectified out
>put of a Variac. A 2.7 Henry inductor was
reduced to a little less
>than 1 Henry with 140 VDC in the control winding,
allowing a small
>light bulb just enough current to give off some
visible light
>(measured current 0.188 Amp with no DC control
and no light to 0.42
>Amp with 140VDC control and visible soft glow
from bulb).
>
>However, all attempts to do this on any large (20
to 250 lbs.)
>inductors controlling a 240 volt circuit in the
30 to 150 Amp range
>have been not only fruitless but have almost
instantly slagged the
>25 Amp bridge rectifier connected to the control
winding.
>
>I need to understand what I am missing here. Any
theory or
>especially winding diagrams of working reactors
would be greatly
>appreciated. I did find one article that
suggested 2 AC power
>windings in series and in phase have to be used
with 2 DC windings
>in series and "out of phase" with each other in
order to cancel the
>effect of induced AC in the control winding. But
here again, no
>practical application, turns ratios, winding
configurations, etc.
>
>Any thoughts?
>
>Thank you, Carl Litton
>
>Memphis HV Group
Date: Wed, 21 Dec 2005 17:28:44 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: m.j.watts@massey.ac.nz
Hi Carl,
Wouldn't the control winding have to be energized with AC to control an AC
waveform?
Malcolm
On 21 Dec 2005, at 15:05, Tesla list wrote:
> Original poster: "Carl Litton" <Carl_Litton@hilton.com>
>
> Does anyone on this list have any experience
building saturable
> reactors for ballasting purposes? I found some
older notes in the
> archive suggesting that a second winding on an
iron core inductor can
> be used to introduce a variable DC voltage that
will give full range
> control of the inductance as the core approaches
saturation.
>
> I have been able to demonstrate the effect on a
small scale with a
> simple step down transformer by putting the
primary in series with a
> 120 VAC ciruit and connecting the the secondary
to the rectified out
> put of a Variac. A 2.7 Henry inductor was
reduced to a little less
> than 1 Henry with 140 VDC in the control
winding, allowing a small
> light bulb just enough current to give off some
visible light
> (measured current 0.188 Amp with no DC control
and no light to 0.42
> Amp with 140VDC control and visible soft glow
from bulb).
>
> However, all attempts to do this on any large
(20 to 250 lbs.)
> inductors controlling a 240 volt circuit in the
30 to 150 Amp range
> have been not only fruitless but have almost
instantly slagged the 25
> Amp bridge rectifier connected to the control
winding.
>
> I need to understand what I am missing here.
Any theory or
> especially winding diagrams of working reactors
would be greatly
> appreciated. I did find one article that
suggested 2 AC power
> windings in series and in phase have to be used
with 2 DC windings in
> series and "out of phase" with each other in
order to cancel the
> effect of induced AC in the control winding.
But here again, no
> practical application, turns ratios, winding
configurations, etc.
>
> Any thoughts? Thank you,
>
> Carl Litton, Memphis HV Group
Date: Wed, 21 Dec 2005 17:29:27 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: BillEaver@aol.com
<http://www.tpub.com/neets/book8/32m.htm>Methods
of changing inductance /mag amps
Just tried this link and it works good. Best info on what you want to do with
reactors.
Denis Despins, KC6TRW
Date: Thu, 22 Dec 2005 12:14:55 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: Ed Phillips <evp@pacbell.net>
Tesla list wrote:
>Original poster: BillEaver@aol.com
><http://www.tpub.com/neets/book8/32m.htm>Methods
of changing
>inductance /mag amps
>
>Just tried this link and it works good. Best info
on what you want to do
>with reactors.
>
>Denis Despins, KC6TRW
Warning! There are problems with both Figures 2-32 and 2-33. OK in principle
but in practice those circuits would result in AC current flowing in the DC
control winding. More common practice would be to use a 3-leg magnetic circuit.
The power winding would be the center one. Outer two windings would carry the
control current and be connected in series such that the magnetic field the
produce would be in the same direction in the center leg but that the induced
voltages from the power winding would cancel out..
Ed
Date: Thu, 22 Dec 2005 12:15:29 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: "D.C. Cox"
<resonance@jvlnet.com>
Yes, I have used a 12 Amp DC control current to control 240 VAC at 30 Amps. It
was wound around the center I section of an E-I core (used pole xmfr core).
Dr. Resonance
>Original poster: m.j.watts@massey.ac.nz
>Hi Carl,
>Wouldn't the control winding have to be energized
with AC to control an AC waveform?
>
>Malcolm
>
>On 21 Dec 2005, at 15:05, Tesla list wrote:
>
> > Original poster: "Carl Litton" <Carl_Litton@hilton.com>
> >
> >
> > Does anyone on this list have any experience
building saturable
> > reactors for ballasting purposes? I found
some older notes in the
> > archive suggesting that a second winding on an
iron core inductor can
> > be used to introduce a variable DC voltage
that will give full range
> > control of the inductance as the core
approaches saturation.
> >
> > I have been able to demonstrate the effect on
a small scale with a
> > simple step down transformer by putting the
primary in series with a
> > 120 VAC ciruit and connecting the the
secondary to the rectified out
> > put of a Variac. A 2.7 Henry inductor was
reduced to a little less
> > than 1 Henry with 140 VDC in the control
winding, allowing a small
> > light bulb just enough current to give off
some visible light
> > (measured current 0.188 Amp with no DC control
and no light to 0.42
> > Amp with 140VDC control and visible soft glow
from bulb).
> >
> > However, all attempts to do this on any large
(20 to 250 lbs.)
> > inductors controlling a 240 volt circuit in
the 30 to 150 Amp range
> > have been not only fruitless but have almost
instantly slagged the 25
> > Amp bridge rectifier connected to the control
winding.
> >
> > I need to understand what I am missing here.
Any theory or
> > especially winding diagrams of working
reactors would be greatly
> > appreciated. I did find one article that
suggested 2 AC power
> > windings in series and in phase have to be
used with 2 DC windings in
> > series and "out of phase" with each other in
order to cancel the
> > effect of induced AC in the control winding.
But here again, no
> > practical application, turns ratios, winding
configurations, etc.
> >
> > Any thoughts?
> >
> > Thank you, Carl Litton
> >
> > Memphis HV Group
Date: Fri, 23 Dec 2005 12:41:15 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: "Mike"
<induction@comcast.net>
Hi Carl,
I already made reply to your post, however in support of your information search
on saturable reactor control, today at work I located and copied 4 prints of
working commercial versions used in induction heaters.
I then scanned them when I got back here at the lab. Please find 4 simple
prints in one zip file, 4 megabytes.
Each file is a JPG format picture of a 8 X 11 paper. Access path is :
www.hot-streamer.com/mike2004/reactor.zip
You will note that most can be wired 240 or 480, also note on a couple prints,
they use "Sa" and "Fa", "Sb" and "Fb" at the terminals on the print. This format
is also used on the DC winding markings. It means Start A, Finish A, etc. This
lets you be certain that you are in phase when jumping them for series and 480
or parallel for 240 regarding the two AC windings. Also, the DC control winding
is marked in this format for cases that have 3 saturable reactors, the control
windings each have references of winding position Vs polarity. Please note
typical per reactor DC control voltages are ~ 25, with three in series and each
shunted with 100 Ohm resistor ~ 100 watt, the control loop voltage is usually
set to max out at ~ 90 volts and 4 or 5 amps. A bit more amps on the real big
machines. Next week or two, if I can cut loose from other stuff at work, I will
try and use the LRC meter to get you some L values on the AC windings as well as
the control windings.
Mike
----- Original Message ----- From: "Tesla list" <tesla@pupman.com>
To: <tesla@pupman.com>
Sent: Wednesday, December 21, 2005 5:05 PM
Subject: Saturable Reactors as Ballast
>Original poster: "Carl Litton" <Carl_Litton@hilton.com>
Date: Fri, 23 Dec 2005 12:41:48 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: FIFTYGUY@aol.com
In a message dated 12/21/05 5:06:32 PM Eastern Standard Time,
tesla@pupman.com writes:
>I need to understand what I am missing here. Any
theory or
>especially winding diagrams of working reactors
would be greatly
>appreciated. I did find one article that
suggested 2 AC power
>windings in series and in phase have to be used
with 2 DC windings in
>series and "out of phase" with each other in
order to cancel the
>effect of induced AC in the control winding. But
here again, no
>practical application, turns ratios, winding
configurations, etc.
I have no experience with Saturable Reactors or Magnetic Amplifiers. But I have
glanced at the theory before, and after your question I figured I'd take a
closer look. It appears that the "out-of-phase" two-winding connection for the
DC control is mandatory to prevent AC from being induced in the control side, as
you have found. Moreover, doing so only suppresses the fundamental frequency and
odd harmonics thereof. Therefore, the flow of even-harmonic currents in the
control winding is a design issue. In fact, there's a distinction between
"free-flow even-harmonic current" and "suppressed even-harmonic current"
designs. To suppress
the even harmonics, the DC control circuits impedance should be high relative to
the induced currents. I've seen mention of filtering chokes in the DC control
circuit. I guess the aim would be to achieve DC control with the lowest DC
current, most control wire turns possible? The correct operation point on the
magnetization curve is also important, as has already been mentioned. As to two
AC ("gate") windings required, I don't see why this would be necessary. One
explanation is that the texts consider a Saturable Reactor as a single DC
winding with a single AC winding. Magnetic Amplifiers are built using one or
more SR's, so a MA built
with two out-of-phase DC windings requires two SR's. This gives the necessary
configuration on the DC side, but you end up with two AC windings. There are
also some distinctions between whether the AC windings
are parallel or series connected. In addition, by putting a half-wave rectifier
in series with each AC winding, but both connected to the load (the two
rectifiers in opposite direction), AC is still run through the load, but the
evil even-harmonic currents are suppressed. Each winding conducts through half
a cycle.
Now for the part where I go off on wild, inexperienced speculation:
It seems to me that the current through the load from an SR/MA is much like that
from an SCR controller, since it's a phase-angle controller. At a controlled
point on the AC wave, the SR goes into saturation, and current through the load
increases. I suppose the advantages of the SR would be that it could be very
simple and very
robust, requiring no tubes or semiconductors to fry (could run off a car
battery). You've also already got the big chunk of iron because of the ballast.
The turn on ramp from the SR might be more gentle than the sudden commutation of
an SCR, so EMI, noise, and di/dt stresses would be less. OTOH, SCR controllers
are very mature technology, and darn tough. they can also be very simple to
install, particularly a single-phase, relatively low-voltage/low current
application such as the input to a pig.
-Phil LaBudde
Date: Fri, 23 Dec 2005 12:42:27 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: FIFTYGUY@aol.com
Folks-
Just like to add that my Miller "Dialarc" welder uses the Saturable Reactor
principle. Instead of transformer taps or a system to mechanically move a core
shunt, a pot on the front adjusts the control circuit. It has a schematic on the
inside cover, but unfortunately, I can't get to it right now to copy it. But the
Miller website has owner's manuals:
<http://www.millerwelds.com/service/ownersmanuals.php>http://www.millerwelds.com/service/ownersmanuals.php
I'm pretty sure this is the one for my welder:
<http://www.millerwelds.com/om/o314v_mil.pdf>http://www.millerwelds.com/om/o314v_mil.pdf
The schematic shows only one DC control winding, but it may really be the two
out-of-phase windings shown as one. Very simple arrangement, with the front
control dial being a 15W rheostat directly controlling the DC control voltage.
Nice to see everything first goes through an isolating transformer (with a
separate winding
to derive the input to the DC control's rectifier). The Magnetic Amplifier
winding interconnections look a little complex, but there's also a high/low
output switch thrown in there for welder output ranges. A full-wave bridge on
the output for DC welding is obviously of no use to us (unless you were
cascading Magnetic Amplifiers, and
needed that kind of output for the control input to another Amplifier!).
Another thing I thought of: keeping the DC control circuit's impedance high
makes it easier to filter (if filtering is desirable?).
-Phil LaBudde
Date: Sat, 24 Dec 2005 09:37:08 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: Finn Hammer <f-h@c.dk>
Tesla list wrote:
>Original poster: "Mike" <induction@comcast.net>
>
>Hi Carl,
Snip
>Next week or two, if I can cut loose from other
stuff at work, I
>will try and use the LRC meter to get you some L
values on the AC
>windings as well as the control windings.
>Mike
Mike,
Pls. notice that few LCR meters can supply enough current to produce a useful
measurement on iron cored inductors. By exciting the windings with a typical LCR
meter, the iron will be operating in the low "initial permeability" area of the
B-H curve, and the readings will turn out to be too small.
Instead, you should connect the windings across a variac, with a Ammeter in
series, and calculate inductance according to:
u = wLi
W = Omega = 2*pi*frequency = 2 * 3.14 * 60 = 377
Cheers, Finn Hammer
Date: Tue, 27 Dec 2005 12:17:25 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: RE: Saturable Reactors as Ballast
Original poster: "Carl Litton" <Carl_Litton@hilton.com>
Thanks, Finn. What is 'u' in your equation - the input voltage?
Carl Litton
-----Original Message-----
From: Tesla list [mailto:tesla@pupman.com]
Sent: Saturday, December 24, 2005 10:37 AM
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: Finn Hammer <f-h@c.dk>
Tesla list wrote:
>Original poster: "Mike" <induction@comcast.net>
>
>Hi Carl,
Snip
>Next week or two, if I can cut loose from other
stuff at work, I will try and use the LRC meter to get you some L >values on the
AC windings as well as the control windings.
>Mike
Mike,
Pls. notice that few LCR meters can supply enough current to produce a useful
measurement on iron cored inductors. By exciting the windings with a typical LCR
meter, the iron will be operating in the low "initial permeability" area of the
B-H curve, and the readings will turn out to be too small.
Instead, you should connect the windings across a variac, with a Ammeter in
series, and calculate inductance according to:
u = wLi
W = Omega = 2*pi*frequency = 2 * 3.14 * 60 = 377
Cheers, Finn Hammer
Date: Tue, 27 Dec 2005 12:17:37 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: RE: Saturable Reactors as Ballast
Original poster: "Carl Litton" <Carl_Litton@hilton.com>
Thanks for that, Phil. The diagram is excellent. Thanks also to everyone who
responded on this issue!
Carl Litton
-----Original Message-----
From: Tesla list [mailto:tesla@pupman.com]
Sent: Friday, December 23, 2005 1:42 PM
To: tesla@pupman.com
Subject: Re: Saturable Reactors as Ballast
Original poster: FIFTYGUY@aol.com
Folks-
Just like to add that my Miller "Dialarc" welder uses the Saturable Reactor
principle. Instead of transformer taps or a system to mechanically move a core
shunt, a pot on the front adjusts the control circuit. It has a schematic on the
inside cover, but unfortunately, I can't get to it right now to copy it. But the
Miller website has owner's manuals:
<http://www.millerwelds.com/service/ownersmanuals.php>http://www.millerw
elds.com/service/ownersmanuals.php
I'm pretty sure this is the one for my welder:
<http://www.millerwelds.com/om/o314v_mil.pdf>http://www.millerwelds.com/
om/o314v_mil.pdf
The schematic shows only one DC control winding, but it may really be the two
out-of-phase windings shown as one. Very simple arrangement, with the front
control dial being a 15W rheostat directly controlling the DC control voltage.
Nice to see everything first goes through an isolating transformer (with a
separate winding
to derive the input to the DC control's rectifier). The Magnetic Amplifier
winding interconnections look a little complex, but there's also a high/low
output switch thrown in there for welder output ranges. A full-wave bridge on
the output for DC welding is obviously of no use to us (unless you were
cascading Magnetic Amplifiers, and
needed that kind of output for the control input to another Amplifier!).
Another thing I thought of: keeping the DC control circuit's impedance high
makes it easier to filter (if filtering is desirable?).
-Phil LaBudde
Date: Mon, 23 Jan 2006 07:02:58 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: RE: Saturable Reactors (fwd)
Original poster: "Jim Mora" <jmora@jetlink.net>
Hello All,
We have been having an on going discussion about ballasting pole pigs and the
effects of the XC/break rate in the secondary, etc reflected back into the
primary ballast XL and resulting in cancellation and higher than
expected currents.
I think it would be an excellent project to come to a suggested saturable
reactor that would be useful to must of the list applications, Sans arc welders,
home depot coils of wire, and MOT strings; if for no other reason
than for safety sake. But such a plan would be great!
Excuse the cross post but your recent threads relate to just that.
Jim Mora
-----Original Message-----
From: High Voltage list [mailto:hvlist@pupman.com]
Sent: Wednesday, January 04, 2006 7:01 AM
To: hvlist
Subject: Re: Saturable Reactors (fwd)
Original poster: Steven Roys <sroys@pupman.com>
---------- Forwarded message ----------
Date: Tue, 3 Jan 2006 21:19:19 -0500
From: Bob Paddock <bob.paddock@gmail.com>
To: High Voltage list <hvlist@pupman.com>
Subject: Re: Saturable Reactors
On Friday 23 December 2005 11:18 am, Carl Litton wrote:
> Does anyone (Doc, Peter, Jim, etc.) on this list
have any experience
> building saturable reactors for ballasting
purposes?
I wrote a couple of papers that touched on these a few years ago for Circuit
Cellar Online. Look at the "High Voltage" and "Metglas (Applications of
Amorphous Metals)" papers in the table near the bottom
of the page at:
http://www.designer-iii.com/
Many of the links no longer work as the papers where written a long time ago in
Internet Time, but still has some useful SR info.
Date: Fri, 17 Mar 2006 19:31:54 -0700
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Saturable Reactor, I have ordered one to test
Original poster: "Jim Mora" <jmora@jetlink.net>
Hello Group,
I struck a deal with the guy on ebay that has real saturable reactors rated @
10kVA. The transformer alone weighs 200 lbs. I is very much like a three phase
reactor with a very big center control winding. The two outer legs are the
controlled single phase. This is rated for 480 use but it looks like there is
two coils per leg so hopefully it can be wired for 220v use.
Someone had a theory that controlling the outer windings with the center winding
of a three phase transformer could not work along the lines that it would in
essence remove itself from the three phase transformer. This would seem not to
be the case. There are six more of these available. They are brand new too.
Three phase transformers seem to be in abundance as well. I believe they could
be made to work nearly as well.
Take a look. ebay # 7573657637 I'll put it under a 10KVA load, vary it to the
extremes, and report back, I'll also monitor the waveform. Mots still are
cheaper but they don't come in a NEMA rated case, and I still contend
the lash up is inherently more dangerous.
Regards to all,
Jim Mora