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Re: Saturable Reactor Ballast - further testing 1 and SAFETY note
Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
If you're stuck without the ability to use the neutral
because you're using a 240V variac instead of ganged
120V variacs to drive your pig, then perhaps the thing
to do is wire all of the series connections between
MOTs (which would otherwise be floating) to the pig
neutral. These would be like a "fake" neutral
connection to the pig. Let the pig LV side act like a
big voltage divider to stabilize the MOT primaries.
There would be no neutral connection from the supply
in this case. Here's a simple two-MOT example of what
I'm talking about, and it can easily scale to any
number of pairs:
http://silicon-arcana.com/MMSR2.gif
Would *that* work? I think it would... IMO, letting
the series MOT connections float isn't just badness,
it's not necessary. At least not *completely* :-)
Regards,
Aaron, N7OE
--- Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>
>
> One possible problem to using the pig neutral is
> that
> lots of folks use single (or parallel) 0-240 volt
> variacs, which places both LV sides at -120 volts at
> zero power. One side stays at -120, while the other
> side goes from -120 to zero, then to +120 as the
> variac is ramped up. (I know it's not really "-" and
> "+", but that's the easiest way to describe it). Of
> course if you use two ganged 120 volt variacs this
> isn't a problem.
>
> Adam
>
> --- Tesla list <tesla@xxxxxxxxxx> wrote:
>
> > Original poster: "J. Aaron Holmes"
> > <jaholmes@xxxxxxxxxxxxxxxxxx>
> >
> > Carl, can you comment on the heating of the MOTs
> > under
> > load? What kind of throughput is reasonable to
> > expect
> > without a lot of fancy cooling? I (and I suspect
> > many
> > others) would love to see a big Jacob's ladder
> > running
> > with this thing as a ballast!!! :)
> >
> > Regarding the 240V approach, see the "Eight-MOT
> > reactor for 240V" at the bottom of the following
> > image
> > (may need to zoom it; it's big!)
> >
> > http://www.silicon-arcana.com/MMSR.gif
> >
> > If you notice, I called out the Neutral
> connection
> > even though it plays no role in the reactor
> itself.
> > Still, if you connect Neutral to the center lug
> of
> > your pig's LV, ballasting the pig can be thought
> of
> > as
> > ballasting two separate transformers, one on Hot
> 1,
> > another on Hot 2. The MOT config on each of
> these
> > is
> > ***absolutely identical*** to the four-MOT
> ballast
> > you're talking about. The only difference is
> that
> > the
> > control windings of each four-MOT pieces are in
> > series. So you see, there is actually *nothing*
> > floating on the power side of things, which IMO,
> > makes
> > it vastly preferrable to putting MOT primaries in
> > series.
> >
> > But, there may be 240V transformers in use in the
> TC
> > community that do not have a Neutral connection,
> in
> > which case you're probably stuck with the series
> > primary arrangement.
> >
> > Regards,
> > Aaron, N7OE
> >
> >
> > --- Tesla list <tesla@xxxxxxxxxx> wrote:
> >
> > > Original poster: "Carl Litton"
> > > <Carl_Litton@xxxxxxxxxx>
> > >
> > > Thank you, Ted.
> > >
> > > This thread seems to have generated some
> > interest.
> > > So, we though some
> > > here might appreciate an update on the 8 MOT
> > reactor
> > > we configured this
> > > past weekend.
> > >
> > >
> http://hvgroup.dawntreader.net/8motreactor2.jpg
> > >
> > >
> http://hvgroup.dawntreader.net/8motreactor1.jpg
> > >
> > >
> > > This concept appears to be amazingly versatile
> > with
> > > a large number of
> > > possible configurations to address the
> particular
> > V
> > > and I parameters of
> > > its intended application. We have verified
> the
> > > hypothesis posted Friday
> > > that the control windings may be placed in
> series
> > > rather than parallel
> > > to give a higher and wider control voltage
> range
> > > without ill affect. In
> > > fact, with the 8 pack above, we placed the
> > control
> > > windings of all 4
> > > pairs of MOT's in one continuous series,
> > resulting
> > > in a control range of
> > > about 0-100 VDC.
> > >
> > > Placing the additional 2 pairs in parallel
> with
> > the
> > > first 2 pairs did,
> > > as expected, drop the high end reactance to 15
> > Ohms.
> > > The low end
> > > remained 2 Ohms.
> > >
> > > READ THIS ****** We also tested the idea
> > suggested
> > > here on this list
> > > that the primaries should be placed in
> 'straight'
> > > parallel - that is the
> > > left input tab of one MOT connected to the
> left
> > tab
> > > of its pair partner
> > > and the right to the right of the other.
> PLEASE
> > > NOTE that this results
> > > in nearly 4000 Volts in the control winding.
> It
> > > appears that if
> > > identical transformers are used, the primaries
> > must
> > > be wired in
> > > 'cross/inverse/anti' (pick a term) parallel -
> > that
> > > is the LEFT input tab
> > > of one MOT is connected to the RIGHT input tab
> of
> > > the other MOT in the
> > > pair and visa versa in order to have low or no
> > > voltage in the control.
> > > Of course, this is predicated on the use of
> the
> > HV
> > > tabs to connect the
> > > secondaries in series, which as you can see is
> > what
> > > we are using.
> > > *******
> > >
> > > There also appears to be no reason that the
> > > primaries of each pair may
> > > not be connected in series (making sure that
> they
> > > are wired such that no
> > > voltage is induced in the secondaries) and
> then
> > the
> > > pairs connected to
> > > each other in parallel. This configuration
> may
> > be
> > > more suitable for
> > > heavy current work in the 200-300 VAC range.
> > >
> > > The suggestion of putting parallel MOT's in
> each
> > > half of the phase in a
> > > 240 VAC circuit may possibly be less
> > satisfactory.
> > > The two legs of the
> > > split phase are only 120 VAC *with respect to
> > > ground.* They are 240 VAC
> > > with respect to each other. The MOT's are
> > floating
> > > in this type of SR
> > > and will be subjected to 240 VAC if placed in
> the
> > > circuit in this
> > > manner. Another consideration is that they
> will
> > > then be 2 inductors in
> > > series and as such, their inductances will be
> > > additive in the circuit.
> > >
> > > More results soon . . .
>
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