Re: Spark gap

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi John,

I think we have all asked this question at one time or another.  "I" even
made a gap like this "once".  ;-)

At 10:10 PM 9/1/2002 -0500, you wrote:
>Hi everyone,
>
>This is only my third post, and I appreciate everyone taking the time to
>answer what may seem to be trivial questions.  Here's another one:  I've
>been hitting all of the sites and the archives concerning rsg's, and I was
>wondering why a gap couldn't be constructed using only two stationary
>electrodes and having small holes drilled in the disc to control firing
>times.  

You can "make" a gap like this (I did).  Making it "work" is the problem :o))

>Wouldn't this help to alleviate problems concerning arcs following
>the electrodes on a standard rotary disc, as well as having very precise
>control over quenching?  

For quenching, the gap only moves a fraction of an inch in the say 0.00005
seconds a coil may need to quench (about 5 degrees).  The disk looks fast
to us, but for quenching, it is as slow as molasses. 

>I'm sure there's a suitable material that could
>handle the high heat as the arc passes thru the holes without eroding it.

No!  There really isn't!! :-))  The arc is about as hot as a plasma torch.
I don't know how hot that is...  Google comes up with a few sites that say
21,000F!! or 11650C :

	http://www.vriffx-dot-com/peps/technical/plasma%20torch.htm

Our gaps probably are not that good but the highest melting point material
is...  Carbon at 3550C.  Tungsten boils at 5930C :


http://www.t30.physik.tu-muenchen.de/lehrstuehle/T32/matpack/html/Nuclear/El
ements/meltboilC.html

So a plasma torch is twice the boiling point of tungsten...  Our normal
gaps are a little lucky in that the highest heat is in the center of the
arc.  The tungsten tips see the "cold" part of the arc ;-)

In my gap, the blades were made of plastic :o))  The arc sliced them right
off...  Some ceramics may have a chance of lasting a "little while".  But
they may shatter under the intense point heat.

>Also a suggestion for those building gaps with tungsten rods-would it help
>to use brass air brake fittings to hold your rods in place?  They can be had
>with pipe thread on one end (easy enough to thread your stationary gap
>blocks on your rsg for these), plus the compression ferrule on the other end
>would allow uniform clamping force all the way around, and if not overly
>tightened can be loosened and the rod slid in our out to make adjustments to
>gap width or compensate for wear.  They come in sizes from 1/8" up.  Just a
>thought.

That sounds like a good idea!!  Are the fitting expensive and where do you
get them?

Cheers,

	Terry

>
>Thanks,
>John Richardson
>