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Re: SUCCESS with Saturable Reactor from MOT's (fwd)
Original poster: Steven Roys <sroys@xxxxxxxxxx>
---------- Forwarded message ----------
Date: Wed, 1 Mar 2006 16:47:56 +1300
From: m.j.watts@xxxxxxxxxxxx
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: SUCCESS with Saturable Reactor from MOT's (fwd)
I have to admit I'm struggling to see the difference between the two
circuits. As long as each pair of transformers have the control
windings oppositely phased it should work shouldn't it? A nice idea
indeed. Reminds me of hybrid telephony circuits in a way.
Malcolm
On 28 Feb 2006, at 7:30, High Voltage list wrote:
> Original poster: Steven Roys <sroys@xxxxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Fri, 24 Feb 2006 07:17:48 +0100
> From: Finn Hammer <f-h@xxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: SUCCESS with Saturable Reactor from MOT's (fwd)
>
> Carl,
>
> Congratulations, this may be the most important discovery in quite some
> time.
>
> I may be wrong, but from the schematic, it would appear that you have
> the secondaries wired in parallel pairs of opposing series, as you describe.
> However, since the primaries are wired in pairs of opposing parallel, it
> would appear to me, that the effect is canseled, and you would in fact
> get voltage on the secondaries/controll windings.
> Therefore I suggest that the schematic does not faithfully record the
> setup as you describe.
> Perhaps this is more what is intended?
> http://home5.inet.tele.dk/f-hammer/satur.jpeg
>
> However, a very clever idea. I have never seen anyone taking the
> controll winding out on 2 separate cores.
>
> Cheers, Finn Hammer
>
> High Voltage list wrote:
>
> >Original poster: Steven Roys <sroys@xxxxxxxxxx>
> >
> >
> >
> >---------- Forwarded message ----------
> >Date: Wed, 22 Feb 2006 08:55:34 -0600
> >From: Carl Litton <Carl_Litton@xxxxxxxxxx>
> >To: High Voltage list <hvlist@xxxxxxxxxx>
> >Subject: SUCCESS with Saturable Reactor from MOT's
> >
> >The following is cross-posted between the 2 lists since we think it will be germane in both arenas:
> >
> >
> >In our research into different types of ballast to control current demand on various projects, w
e found that it is often useful to be able to vary the current independently of the voltage if a si
ngle power supply is to be used for multiple projects with different V and I requirements. In the p
rocess, we ran across the concept of the Saturable Core Reactor. The idea is simple. Introduction
of a small variable DC voltage into a separate winding on an iron frame inductor will bring the co
re to saturation, opposing the inductance of the power winding. The closer to saturation the core
becomes, the lower the inductance of the reactor and the larger the current that is allowed to flow
. We find this concept intriguing because it offers infinitely variable control of large currents
by way of a low power control circuit. We have conducted several experiments on this subject and
will publish a comprehensive article when all of the data is in. However, our most recent experime
ntal configuration has given such remarkable results that we find it worthy of being reported separ
ately.
> >
> >One of the major drawbacks to creating a saturable reactor from scratch is the requirement that
the control winding consist of 10-100 times the number of turns as the power winding in order to pe
rmit control of the power winding with low current DC. If the power and control windings have the
same number of turns, then it will require 100 Amps in the control winding to regulate 100 Amps in
the power winding. This is hardly efficient. With 10 times the number of turns, control of 100 Am
ps would require only 10 Amps DC and with 100 times the number of turns, only 1 Amp would be necess
ary. The winding of several thousand turns on a transformer is daunting to say the least. We have
therefore been looking into the use of transformers with configurations that would require the lea
st amount of modification. In the process, we have worked with several core types: round, EI, figu
re 8, etc. A recent post to the HV list by Aaron Holmes suggested the possibility of using two sep
arate transformers. Having a huge supply of MOT's many of which are identical in brand and model n
umber, we decided to test this concept. We are pleased to report a very successful result.
> >
> >Two pairs of MOT's were selected. Each MOT was of the older stouter design type, weighing aroun
d 15 lbs. and possessing heavy gauge primary windings. For each pair, the primaries were wired tog
ether in parallel. The secondaries were placed in series by connecting the HV tab of each unit and
connecting a wire to the frame of each by means of a bolt run through one of the mounting hotels i
n the frame. These output wires were connected to the HV side of a 125:1 NST to which a DMM was co
nnected to the LV side. 0-145 VAC was introduced into the parallel MOT primaries while monitoring
the DMM for voltage. If no voltage registered, the DMM was moved to the HV side of the NST and the
procedure was repeated. A value of 30 Volts or less indicated a successful series connection in t
he 'opposing' sense and confirmed that the transformers chosen were close enough to identical to pr
oceed. If the first test had indicated significant high voltage output, one pair of wires in the p
arallel primary connection was swapped and the test repeated to confirm that the seriesed secondari
es no longer registered significant voltage.
> >
> >Direct measurement of the inductance of the paralleled primaries was then performed with an amme
ter in series with the input supply circuit set at 35 VAC. The ammeter registered about ? Amp, ind
icating a baseline inductive reactance of around 60 Ohms. The ends of the seriesed secondary circu
it were the wires attached to the frame of each transformer. This series forms the DC control wind
ing. These wires were attached to the rectified output of a small Variac. The introduction of 0-82
VDC into the control caused the reading on the ammeter to increase smoothly over the range to a fi
nal value of 16.9 Amps. We did not push this further due to the 20 Amp limitation of the ammeter,
but this corresponds to an inductive reactance of slightly over 2 Ohms, making the test a resoundin
g success. With cooling, this pair could reasonably be expected to handle 40 or 50 Amps as ballast
and the other pair gave a very similar test result.
> >
> >The question then became whether the two pairs could be successfully paralleled for higher curre
nt handling capability. To this end, shunt wires were run to connect two sets of paralleled primar
ies. Then, the two sets of seriesed secondaries were connected in parallel with respect to each ot
her. A brief power test was performed just to insure that no voltage was induced into the control.
At this point, the inductance/saturation testing was repeated on the combination of all 4 MOTS.
The testing was also very successful and the results very similar to those from the tests of the i
ndividual pairs with a couple of exceptions, which are as follows. First, the baseline reactance w
as reduced to about ? of the value measured on the individual pairs - 30 Ohms instead of 60. This
was to be expected pursuant to the law of parallel inductors. Second and more surprising, there wa
s only required a total of 28 VDC in the control to reduce this value to 2 Ohms. It would seem to
follow that more pairs could be added with a corresponding increase in current capability and decre
ase in baseline reactance. The high end reactance drop should not resent a problem since the usefu
l range of inductive reactance for most of our project work is about 2-8 Ohms.
> >
> >An admittedly poor but serviceable photo of the 4-MOT reactor stack has been placed here:
> >
> >http://hvgroup.dawntreader.net/srmots.jpg
> >
> >The schematic is here:
> >
> >http://hvgroup.dawntreader.net/4motreactor.jpg
> >
> >
> >
> >We'd love to repeat this experiment with a pair of identical transformers removed from 5 or 10 k
VA pole pigs, but alas, they are not a plentiful as MOT's around here.
> >
> >
> >Questions/comments are welcome.
> >
> >
> >Carl Litton
> >Memphis HV Group
> >
> >
> >
> >
> >
> >
> >
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