Re: Spark Gap

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

Original poster: "CJ Moore by way of Terry Fritz <twftesla-at-qwest-dot-net>" <wizard1234-at-home-dot-com>

I hate to ask this, but since most people seem to be mentioning them and I
gather they are important, what are MOV's?

----- Original Message -----
From: "Terry Fritz" <twftesla-at-qwest-dot-net>
To: "CJ Moore" <wizard1234-at-home-dot-com>
Sent: Wednesday, July 18, 2001 3:46 PM
Subject: Re: Spark Gap


> Hi CJ,
>
> At 03:26 PM 7/18/2001 -0700, you wrote:
> >If I haven't made the primary coil yet, can I just wrap some thin wire
> >around a pipe and use it to limit the current?
>
> Sure,  Since the RMS current is low, even thin wire will work fine.
>
> >Also I put the fuses on each
> >input of the NST's? So 4 total? You say that the fuse will limit the
current
> >if you internal shunts forget to, so if the internal shunts go haywire,
the
> >fuses will limit the current supplied to the NST's thereby saving the
> >capacitor hopefully?
>
> Yes.  When NSTs start to go nuts, they draw a ton of current.  Simple
fuses
> will stop the destructive process.
>
>
> >Does this mean that the NST's are shot now?
>
> They should be fine.  When/if they will no longer draw an arc to the case
> or anything, then they are toasted.
>
> >About the
> >NST hookup, they are each 9kv 60 ma, and I want to get 9kv 120 ma. They
are
> >center grounded. Do I not ground the cases to the ac ground?
>
> Yes, ground the metal casses and hook them up in parallel like the diagram
> I sent.
>
> Cheers,
>
> Terry
>
>
> >
> >----- Original Message -----
> >From: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >To: "CJ Moore" <wizard1234-at-home-dot-com>
> >Sent: Wednesday, July 18, 2001 11:37 AM
> >Subject: Re: Spark Gap
> >
> >
> >> Hi CJ,
> >>
> >> At 09:19 PM 7/17/2001 -0700, you wrote:
> >> >
> >> >
> >> > ----- Original Message -----
> >> > From: <mailto:wizard1234-at-home-dot-com>CJ Moore
> >> > To: <mailto:twftesla-at-qwest-dot-net>Terry Fritz
> >> > Sent: Tuesday, July 17, 2001 5:31 PM
> >> > Subject: Re: Spark Gap
> >> >
> >> > I don't want to sound like an idiot, but I don't really have that
much
> >> > knowledge (actually very little). So I was wondering if you could be
a
> >little
> >> > more specific? I really don't want to damage my cap, and the setup I
> >> > described is very similar to how my tesla coil operated. If this is
bad
> >I
> >> > would like to know how to correct it. Several questions:
> >> > 1) How do I limit the current?
> >>
> >>
> >> Normally, a Tesla coil has a primary inductor that the cap discharge
> >through.
> >> This inductance acts much like a resistor in that it will limit the
> >current.
> >> With the gap right across the capacitor, there is not too much to limit
> >the
> >> current except the wire resistance which is really low.  If you have a
> >primary
> >> coil, I would wire in series with the cap.
> >>
> >>
> >> >
> >> > 2) Where do I put the device in the circuit?
> >>
> >>
> >> In series with the cap would be fine.
> >>
> >> >
> >> > 3) Why do I want to limit the current if I want the big sparks?
> >>
> >>
> >> The current can get too high.  10,000, 20,000, 50,000 amps....  No one
> >knows
> >> how much current a good short across a high energy pulse cap is.  But
if
> >you
> >> get too much, the internal connections in the cap will blow out.
> >>
> >> >
> >> > 4) Is an inductor similar to a choke?
> >>
> >>
> >> Yes.   But, a primary coil is built to take high voltage where a common
> >chock
> >> may short.
> >>
> >>
> >> >
> >> > 5) Would something like your NST protection circuit work in a
situation
> >like
> >> > this?
> >>
> >>
> >> It would not limit the current from the primary cap but it would help
> >protect
> >> the transformer.
> >>
> >> >
> >> >
> >> > If you can answer these questions more directly with a simple answer
> >please
> >> > do so, as I don't want to waste your time. I attached a picture that
I
> >drew
> >> > of how I have it hooked up, because I don't trust myself to draw the
> >> > schematic correctly.
> >>
> >>
> >> I would also put a fuse on the input of each NST.  About 3 amps.  There
is
> >a
> >> chance that your cap and NST combination could saturate the NST current
> >> limiting cores and blow the NST.  The fuse will limit the current if
the
> >> internal shunts in the NST forget to ;-)
> >>
> >> I would also think you would want to hook up the NSTs like the enclosed
> >> diagram.  If your NSTs are center grounded, then you only get 9kV at 30
> >MA.
> >> This way you get 9kV at 60 mA.  If your NSTs are not center grounded,
then
> >you
> >> would get 18kV at 30mA.
> >>
> >>
> >> >
> >> >
> >> > Thanks again for all your help
> >> >
> >> >
> >> > BTW: I got some caps rated at .02 uf 16 kvdc and I used them in
series
> >(I
> >> > think) with the two transformers and I got 4-5 inch arcs from a
Jacobs
> >ladder
> >> > type device, but after a few minutes of operation the a little hole
in
> >the
> >> > cap blew out. It looks sort of like somebody shot a small bb through
it.
> >So
> >> > they do blow up
> >>
> >>
> >> Hard to say why.  Could have been the wrong cap material.  If they got
> >hot,
> >> they probably were not polypropylene which is about the only suitable
> >material.
> >>
> >> Hope this helps...
> >>
> >> Cheers,
> >>
> >>         Terry
> >>
> >>
> >> >
> >> >
> >> >
> >> >
> >> > _________________________________________________________________
> >> > Hi CJ,
> >> >
> >> > A cap connected just to the NST may ring up the voltage really high.
If
> >you
> >> > hit the 60Hz resonant point you can get like 80000 volts!  that will
> >blow
> >> > something up so be careful.  When the cap arced, was there anything
to
> >limit
> >> > the current?  If you have 20000 volts but no inductor and no
resistance,
> >the
> >> > current will be super high.  20000 volts into 1 ohm is 20000 amps.
That
> >will
> >> > be loud :-)  Super high current like that can damage the cap too.
Best
> >to
> >> > add
> >> > an inductor to act as a current limit.
> >> >
> >> > Cheers,
> >> >
> >> >         Terry
> >> > __________________________________________________________________
> >> >
> >>
> >>
> >>
> >
>