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

• To: tesla-at-pupman-dot-com
• Subject: Re: Low voltage sparkgaps for ignition coil driver...
• From: Jim Lux <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
• Date: Tue, 24 Nov 1998 11:16:53 -0700
• Approved: terryf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
> 
> Tesla List wrote:
> 
> > The dielectric strength of air is 20k(!!)V per mm not 20v/mil.
> 
> 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). This is a real problem in
designing high power radio equipment (like radars) to operate in the
upper atmosphere.

More on the Paschen stuff on my page at
http://home.earthlink-dot-net/~jimlux/hv/paschen.htm


-- 
Jim Lux                               Jet Propulsion Laboratory
ofc: 818/354-2075     114-B16         Mail Stop 161-213
lab: 818/354-2954     161-110         4800 Oak Grove Drive
fax: 818/393-6875                     Pasadena CA 91109

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