RE: Saturable Reactor Ballast for TC from MOT's, or heavier 3 phase Transformers.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

Let us know how it goes!  It may be totally acceptable
to use the center winding for the control rather than
the outer windings, however I suspected it might be
easier to saturate by controlling the outer two
windings.  This is because, in a typical three-phase
core, each of the legs has the same cross-sectional
area.  Could you then saturate the outer legs by
controlling only the middle leg?  Without the power
winding in play, probably not.  But with a lot of
current in the power winding, probably so.  I don't
have the experience to say.  In the commercial SR's
that I've seen, the center leg of the core appears to
have double the cross-sectional area of each of the
outer legs, suggesting that saturation of the outer
legs is possible with only the center winding in play
(and in fact, all the commercial SR's I've seen use
the middle winding for the control).

I saw a beautiful little 3kVA 4160V-240V three-phase
dry-type transformer go by on eBay last week.  Seemed
like just the thing, but the guy wanted like $400 for
it!  Nuts!!

Regards,
Aaron, N7OE


--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
>
> Hi Aaron, Et Al,
>
> I cross posted an interest in this discussion to the
> HV list a few weeks ago
> as I would like to get the 1256D variac and arc
> welder out of the picture. I
> have a three phase plate transformer en route from
> the Midwest (I'm in ca.).
> I plan to use for multi 833a in the future but it is
> close to what you are
> talking about 240V in 5KV out rated at 1 amp, 70Lbs
> worth. I figure the
> outside windings have to be DC opposing but I don't
> know the math to calc
> this as I stated in my previous post. I have a 5KVA
> 14,400 pig and a number
> of dummy 240v loads up to 13,500 watts @240v if you
> or someone can give me
> some guidance on the DC side, I'll try to lash this
> thing up as you suggest.
> I'll measure the inductance when it arrives which
> should be within a week.
>
> Regards,
> Jim Mora
> Ojai, Ca.
>
>
>
>
> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Saturday, February 25, 2006 3:04 PM
> To: tesla@xxxxxxxxxx
> Subject: Re: Saturable Reactor Ballast for TC from
> MOT's
>
> Original poster: "J. Aaron Holmes"
> <jaholmes@xxxxxxxxxxxxxxxxxx>
>
> Perhaps Carl can report on this?  Anyway, there is
> certainly a rather low limit to how much power a
> single MOT pair will tolerate (unless you've got
> real
> beefy MOTs).  Multiple pairs are definitely in order
> for ballasting pole transformers!  'course, you
> could
> always sink your MOTs in transformer oil and
> probably
> squeeze a few more amps through them :)  I don't
> know
> why cooling the windings should be such an issue
> unless you're really trying to get away with
> something
> (pumping 20, 30, etc. amps through a single MOT).
>
> Alternatively, something I'd really like to see done
> is using a relatively HV (e.g., 4160V-480V)
> three-phase transformer for a SR:  Use the outer two
> HV windings for the control (re-connecting them so
> the
> flux cancels out in the center leg of the core),
> then
> use the middle LV winding for the power winding.
> Seems it ought to work, and I think Carl actually
> tried this with a lower-voltage three-phase
> transformer, but ended up needing too much control
> current.  Still seems a 4160V transformer or
> something
> in that neighborhood ought to solve that issue, but
> where to find one cheap (and local)?
>
> Regards,
> Aaron, N7OE
>
> --- Tesla list <tesla@xxxxxxxxxx> wrote:
>
>   > Original poster: "Peter Terren"
>   > <pterren@xxxxxxxxxxxx>
>   >
>   > This sounds great but...
>   > Has anyone tested it at full power or calculated
>   > dissipation at full power. It strikes me that
> the
>   > losses will be effectively resistive (or rather
>   > heating) with a saturated core and that this
>   > power will go to heat in the MOT core (unlike a
>   > perfect inductor which will have no heating
>   > loss).  I am not clever enough to do the sums
>   > here but guess that the greatest dissipation
>   > would occur when there is equal power loss in
> the
>   > ballast and load (half power) ie 20 A 55V which
>   > would give a power loss of less than 1.1kW
> spread
>   > over 2 MOT core as the cores are not fully
>   > saturated. Added to that is the power of the
> control
>   > winding (?80V 1 amp).
>   > I guess that this is OK for a 2kW load but
> wonder
>   > about higher loads and perhaps this is why the 4
>   > MOT setup is proposed.What I am saying is that
>   > cooling the saturated cores may be an issue but
>   > is probably lesss so than cooling heat from the
>   > windings.
>   >
>   > Peter
>   > http://tesladownunder.com/
>   >
>   > ----- Original Message ----- From: "Tesla list"
>   > <tesla@xxxxxxxxxx>
>   > To: <tesla@xxxxxxxxxx>
>   > Sent: Saturday, February 25, 2006 1:55 AM
>   > Subject: Saturable Reactor Ballast for TC from
> MOT's
>   >
>   >
>   > Original poster: "Carl Litton"
>   > <Carl_Litton@xxxxxxxxxx>
>   >
>   > There have been several questions on this list
>   > recently, regarding variable inductance ballast
>   > for coiling.  What follows is the report of our
>   > successful construction of a saturable core
>   > reactor that allows regulation of current on a
>   > 120 VAC circuit between 4 and 60 Amps with a low
>   > voltage and current DC control circuit.  The
> best
>   > part is that this has been built essentially
>   > without cost, utilizing 4 microwave oven
>   > transformers.
>   >
>   > In our research into different types of ballast
>   > to control current demand on various projects,
> we
>   > found that it is often useful to be able to vary
>   > the current independently of the voltage if a
>   > single power supply is to be used for multiple
>   > projects with different V and I requirements. In
>   > the process, 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 core 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 experimental configuration has given
>   > such remarkable results that we find it worthy
> of
>   > being reported separately.
>   >
>   > 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 permit 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 Amps would require only 10
>   > Amps DC and with 100 times the number of turns,
>   > only 1 Amp would be necessary.  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 least
>   > amount of modification.  In the process, we have
>   > worked with several core types: round, EI,
> figure
>   > 8, etc.  A recent post to the HV list by Aaron
>   > Holmes suggested the possibility of using two
>   > separate transformers.  Having a huge supply of
>   > MOT's many of which are identical in brand and
>   > model number, 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
> around
>   > 15 lbs. and possessing heavy gauge primary
>   > windings.  For each pair, the primaries were
>   > wired together in parallel.  The secondaries
> were
>
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