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Re: Low voltage sparkgaps for ignition coil driver...



Tesla List wrote:
> 
> Original Poster: "chris morgan" <crmorgan-at-hotmail-dot-com>
> 
> >> > 30 kV/cm, or 3 kV/mm, or 76 kV/inch, or 76 V/mil, is a better
> figure.
> >> > But I read somewhere that less voltage than about 240 V (or
> >> > something in this range) cannot cause air breakdown, no matter
> >> > what is the distance. (Does someone know more about this?)
> >>
> >> This is true.. If you look at the Paschen curve, it has a minimum at
> >> some combination of density and distance. If you reduce the distance
> >> even further, the breakdown voltage actually goes up.
> >>
> >> It has to do with the mean free path of the ions in the gap. If the
> gap
> >> gets very small, a cascade of ionization can't develop.  The worst
> >> pressure, from a breakdown standpoint, is around .01 Atmosphere,
> >> equivalent to about 30 km altitude (100 kFt
> 
> If this is true(If you reduce the distance even further, the breakdown
> voltage actually goes up.) couldn't a high capacity high voltage cap be
> made where as the plates were brought together both the capacitance and
> the voltage rating improved?

Sure could, except, how would you connect to the plates, except with a
wire that at some point being the "wrong" distance apart. Perhaps if you
had two Rogowski profile electrodes with the terminals brought out of
the back side perpendicular to the front face of the electrodes.

This peculiarity is of most interest where you have some leads that
transition from an insulator of relatively high dielectric strength into
a vacuum. For instance a vacuum capacitor, of which Jennings makes fine
examples, often used as high voltage RF transmitter caps. Quality
craftsmanship, easy adjustibility, high breakdown voltage, high price...

Then, also there is the issue of getting a high enough capacitance in a
reasonable size to be useful.
> 
> Chris, via the inter-thingy
> 
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-- 
Jim Lux                               Jet Propulsion Laboratory
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