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Re: Spark gap not firing

Original poster: "Matus-at-snet-dot-net by way of Terry Fritz <twftesla-at-uswest-dot-net>" <matus-at-snet-dot-net>

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, February 03, 2001 12:22 PM
Subject: Re: Spark gap not firing

> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> In a message dated 2/2/01 8:45:06 PM Pacific Standard Time,
> writes:
> << I
>  built a foil stack capacitor composed of five aluminum flashing plates
>  were 5" x 7"  sandwiched in between them was a rubberized adhesive
>  which I do not know the exact K value for.  The rubber adhesive was four
> inches
>  across and covered the length of the aluminum plate, giving a capacitor
> of
>  4" x 7". The rubber layers is about 1/64" of an inch across. >>
> Michael,
> I would say that your cap is shorting your NST out. You say that the
> plates are 5" x 7" but your rubber adhesive strip is only 4" wide, if I'm
> under-
> standing you correctly. The dielectric MUST must exceed all deminsions of
> the conductor plates or the HV will easily arc around the egdes of the
> tric or worse yet, the foil plates will lay on each other where they
> the
> dielectric and completely short out the transformer.

I should have been more clear on that.  The flashing that I bought was 5x7
but the rolled rubber adhesive was only 4x7.  So I let one inch hang over
the edge on either side to equate one terminal of the cap.  the different
plates were never directly over one another.  Looked like this

---------------                 (+)
     ==========            K
        ------------------     (-)
     ==========            K
---------------                    (+)
     ==========            K
        ------------------    (-)

etc. etc.

The dialectric had a 1/4" over hang on the sides where the opposite plates
were close to one another, although that might not have been enough.

You need at least a 1"
> clearance of dielectric on all sides of the conductive plates, i.e.- 6" x
> conduc-
> tive plates need at least  8" x 8" dielectric plates between them.
> Also, you will definitely need a dielectirc thicker than 1/64" for a Tesla
> service
> capacitor. And it will need to be oil-filled and vacuumed down or it will
> surely
> fail. In my opinion, if you can afford it, you need to buy some of Terry's
> Pana-
> sonic .056 uFD MMC caps and build your cap from that.

Where do I buy those?

 I think this would
> save you a lot of headache in building your capacitor.

I think so as well, although I would like to get one to work so I at least
know how to do it! =)

 I've successfully built
> homemade caps that would hold a charge and give a visible spark discharge,
> but I have never successfully built one that was suitable for Tesla
> Some people have, but most them had skills and facilities  that are beyond
> the average hobbiest reach. And in the long run, it would probably be a
> cheaper for you to buy the MMCs than to buy the polyethylene sheets and
> alum. flashing and then it fail on you anyway :-(

good point


> My $.02 worth,
> David Rieben