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Re: 6" Coil Problems
Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
With a 12/60 the only gap you need is 2-3 gaps. 12 is way too much because
your are wasting a lot of energy in just heating up the gaps and ionizing
the air. Two is probably the best number and 3 as a max.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Tuesday, September 24, 2002 11:36 AM
Subject: Re: 6" Coil Problems
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> Hi Jonathon,
> At 09:22 PM 9/23/2002 -0400, you wrote:
> >Hello everyone, (forgive me for this being long, there is a lot to
> >:-\ .)
> > I've had my coil put away for a while, and recently brought it out
> >some tests.
> > If you don't know, my coil is as follows:
> >- 12/60 NST
> >- Terry Filter
> >- Multi - Pipe Static Spark Gap ( 12 gaps, each at .025" )
> >- .017 uF Geek Cap
> >- 10 turn, .25" Cu pipe primary coil
> >- 6" * 30" (Wound) secondary coil, #20 AWG wire.
> >- Controller consists of just a switch/light combo, and one outlet.
> >Max sparks to date were 22" Ok, for my first coil, but a 12/60 should
> >more. The problem during the first runs was that the spark gap would only
> >fire at 3 or less gaps! That is only .075 total gap! And never once did
> >properly set safety gaps fire.
> A 12/60 coil can do 45 inch arcs according to John's formula if everything
> is perfect.
> >Yesterday, I had just my NST, filter and spark gap hooked up, to see how
> >gaps that would let me use. Suddenly there was smoke coming from
> >which later turned out to be a MOV in the filter. :-( While investigating
> >smoke, I noticed a piece of what I think is soldier, stuck under the
> >the MOV array, making contact with at least two of the MOVs. I removed it
> >tryed again. I guess MOVs fail closed, because I let the smoke out of a
> >second MOV.
> If the MOVs really overheated bad, you will have to replace all the MOVs
> that leg. MOVs limit voltage well and recover, but it sounds like they
> have been pushed to the point where they start to short out permanently.
> The leads are soldered inside them. If the solder melts, it flows inside
> the move and basically shorts it out.
> >I believe the soldier shorted out one half of the MOVs, which lowered the
> >voltage at which they clamp. This level was under half of my NSTs
> >they were sitting there, dead short to ground. I guess the 60mA for a
> >burned it up. When the one failed, the same scenario occured, and the
> >MOV failed. Does that make sense to every one?
> Yes, The MOVs on that leg have probably all shorted or now have vastly
> reduced voltage.
> >After that I connected the NST straight to the Spark gap, with no filter,
> >or anything. It let me use all 11 or 12 (I forget the total) gaps.
> >that my NST was still OK, I took out the actual filter, but left the
> >resistors, and the safety gaps in circuit. That gave me max of 7 gaps,
> >more and the safety gaps would fire. Sounds good to me.
> Sounds fine.
> >Now that makes me wonder, how long has that short been in the filter?
> >that have been giving me the less-than-satisfactory performance before?
> The MOVs would not suck up power very long. If your runs were short, it's
> possible they would not obviously burn up. However, the MOVs will not run
> very long at all if there were a serious problem.
> >would like to try the coil now, but I am a bit worried about the filter
> >being in there. I still have the safety gaps (which seem to work now) and
> >power resistors in place, and I know that some people use NSTs with out
> >protection at all. But hey, I'm 14, and poor; I have built a Tesla Coil
> >just bought an electric guitar, so I dont feel like burning up this NST.
> The safety gaps will help a lot. You are "90%" safe ;-) Depends on how
> lucky you feel... Normally the MOVs don't do anything. They are just a
> last chance NST saving safety backup when everything else goes wrong.
> >Would it be ok to run the coil the way it is?
> >I thank you for reading this, and hope to get this working right...
> >Jonathon Reinhart