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RE: [TCML] Series Transformers
My experience to date has been strictly with NST's, so take what I say with a grain of salt. But the experience of others as reported on this List is that static gaps perform poorly with high current transformers. Yes, I suspect that quenching will be the issue.
I would fear that a rotary gap would need its electrodes set precariously close, especially since the total gap needs to be divided into two segments. But you didn't hear me say that it can't be done!
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Phillip Slawinski
> Sent: Wednesday, June 18, 2008 8:11 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Series Transformers
>
> I have already built a sucker gap, and it seemed to do a decent job
> quenching. This of course was with a .013 mfd cap. I suppose when the full
> 1mfd + cap is hooked up the quenching will worsen? Why do you say a rotary
> gap is probably not advisable, electrode spacing has to be too close for
> comfort?
>
> On Wed, Jun 18, 2008 at 6:41 AM, Lau, Gary <Gary.Lau@xxxxxx> wrote:
>
> > 2970V @800mA will be challenging. Despite many who thought 4kV is too low
> > for a coil, I built a very efficient coil using a 4kV/20mA NST, using a
> > single static cylinder gap. While it may be possible to get a static gap to
> > work at 2970V, the 800mA part may be difficult to quench. At that low a
> > voltage, an RSG is probably not advisable. You would also need a very large
> > cap to utilize the full potential of that power supply.
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > > -----Original Message-----
> > > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > > Behalf Of Phillip Slawinski
> > > Sent: Tuesday, June 17, 2008 9:21 PM
> > > To: Tesla Coil Mailing List
> > > Subject: Re: [TCML] Series Transformers
> > >
> > > I have a nice variac 20A rated and 0-270V output with 120V in. I was
> > able
> > > to wire them in series and ran them up to 2970V @ 800mA. Is 2970V too
> > low
> > > to run a TC efficiently?
> > >
> > > On Tue, Jun 17, 2008 at 5:13 PM, David Speck <Dave@xxxxxxxxxxxxxxxx>
> > wrote:
> > >
> > > > OK, Phil,
> > > >
> > > > Looks to me like you want to step 110 VAC to perhaps 1100 VAC.
> > > >
> > > > If they are identical transformers, then their internal polarities are
> > > > probably the same. (But you can't count on that!)
> > > >
> > > > Wire the two primaries in parallel. Connect the high voltage output
> > end of
> > > > one transformer secondary to the low voltage end of the other
> > secondary.
> > > > Power up the pair with a Variac set on a very low voltage, say one
> > volt.
> > > > Measure the voltage from the low end of the first transformer
> > secondary to
> > > > the high end of the second transformer secondary. If you have the
> > > > connection right, then you should see something like 11 volts. You can
> > then
> > > > crank up the Variac voltage slowly to confirm that you see a
> > corresponding
> > > > increase in the output voltage at the high end. Remember that Variacs
> > do
> > > > not provide any line isolation, and even at a one volt output, the
> > "hot" end
> > > > of the Variac output is still at line potential and can deliver a
> > lethal
> > > > shock.
> > > > If you don't see any voltage, check the output across each of the
> > > > transformers, to make sure that one of them is not open. If both are
> > > > putting out about 5.5 volts individually, then you have the secondaries
> > > > connected wrong. Just swap the link between the two secondaries to the
> > > > opposite secondary pin on one transformer (with the power off!) and
> > recheck.
> > > >
> > > > A small word of warning -- many digital voltmeters (both cheap and
> > > > expensive) can give spurious readings when used to measure unloaded
> > > > transformers. You may get much more sensible readings if you parallel
> > a 1K
> > > > to 10K ohm power resistor across the inputs to your voltmeter. I once
> > > > wasted a half a day trying to figure out the transformer of a bandsaw
> > blade
> > > > welder with a good Fluke DVM. The readings were all over the map, and
> > often
> > > > inconsistent and unrepeatable. Putting a load resistor on the meter
> > made
> > > > everything work out sensibly.
> > > > 1100 VAC isn't going to help you a lot for TC work. You might be able
> > to
> > > > get away with seriesing 4 transformers for 2200 volts, but at this
> > point,
> > > > you will begin to stress the insulation between the windings and the
> > cores.
> > > > I've read of 4 and 6 MOT series strings, but the outer transformers on
> > the
> > > > 6 MOT strings had to be run under transformer oil to prevent winding to
> > core
> > > > voltage breakdown. OTOH, the power output of a 6 MOT string (~12 KVAC
> > at
> > > > 500 mA, if you use big MOTs), can compare favorably with a 5 KVA pole
> > pig,
> > > > just not so nice and compact, but nearly free, if you can find the
> > MOTs.
> > > > HTH,
> > > > Dave
> > > >
> > > >
> > > > Phillip Slawinski wrote:
> > > >
> > > >> Step Down transformers run in reverse. The transformers have taps for
> > > >> neutral 100V 110V on the primary. On the secondary neutral 420 480
> > 550.
> > > >>
> > > >> On Tue, Jun 17, 2008 at 1:39 PM, David Speck
> <Dave@xxxxxxxxxxxxxxxx>
> > > >> wrote:
> > > >>
> > > >>
> > > >>
> > > >>> Phil:
> > > >>>
> > > >>> What kind of transformers?
> > > >>>
> > > >>> You can't series NSTs, 'cause they are center tap grounded. You can
> > > >>> parallel them for more current, though.
> > > >>>
> > > >>> Dave
> > > >>>
> > > >>> Phillip Slawinski wrote:
> > > >>>
> > > >>>
> > > >>>
> > > >>>> Does anyone know of a way to wire two transformers so that they are
> > > >>>> oppositely phased?
> > > >>>>
> > > >>>
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