Re: 6" Coil Problems

["Tesla list" <tesla-at-pupman-dot-com>]

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.

Dr. Resonance



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <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
include
> >:-\   .)
> >
> >       I've had my coil put away for a while, and recently brought it out
for
> >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
deliver
> >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
the
> >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
many
> >gaps that would let me use.  Suddenly there was smoke coming from
somewhere,
> >which later turned out to be a MOV in the filter. :-( While investigating
the
> >smoke, I noticed a piece of what I think is soldier, stuck under the
leads of
> >the MOV array, making contact with at least two of the MOVs. I removed it
and
> >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
on
> that leg.  MOVs limit voltage well and recover, but it sounds like they
may
> 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
voltage, so
> >they were sitting there, dead short to ground. I guess the 60mA for a
while
> >burned it up.  When the one failed, the same scenario occured, and the
second
> >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,
cap
> >or anything. It let me use all 11 or 12 (I forget the total) gaps.
Pleasing,
> >that my NST was still OK, I took out the actual filter, but left the
power
> >resistors, and the safety gaps in circuit. That gave me max of 7 gaps,
any
> >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?
Could
> >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.
>
> >I
> >would like to try the coil now, but I am a bit worried about the filter
not
> >being in there. I still have the safety gaps (which seem to work now) and
the
> >power resistors in place, and I know that some people use NSTs with out
any
> >protection at all. But hey, I'm 14, and poor; I have built a Tesla Coil
and
> >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...
>
> Cheers,
>
> Terry
>
> >
> >---------------------------------------
> >Jonathon Reinhart
> >hot-streamer-dot-com/jonathon
> >
>