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Re: Low voltage sparkgaps for ignition coil driver...
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> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Low voltage sparkgaps for ignition coil driver...
> Date: Saturday, November 21, 1998 9:32 AM
>
> Original Poster: "James" <elgersmad-at-email.msn-dot-com>
>
> I'm surprized that you didn't think of using just a spark gap that
was
> rated, or just gapping a spark plug 20v/mil then run it through the
primary.
> Dielectric of air = 20volts to the millimeter.
Air is 31 kV/millimeter in uniform field at usual pressures, etc. That's
3000 V/mm, not 20 volts millimeter as stated above. In Inch kind of units,
figure 70 kV/inch (or 70 V/mil). I might add that a nominal .030 inch gap
for automotive applications would break down at 2 kV in normal air, but in
air at 10 times the normal density (that compression ratio thing, after
all), it takes 20 kV+ to break it down.
From: "Jim Lux" <jimlux-at-jpl.nasa.gov>
<<<< I normally don't get involved with how accurate a post is. I assume
we will all figure it out eventually. However, this thread seems to just
get worse as time goes on! :-) I think Jim meant "Air is 3.1kV/mm" in the
first line. Electrical breakdown in air, in short distances, is very
non-linear and dependant on the shape of the electrodes. You will see all
kinds of values. A number like 50kV/inch really doesn't have too much
meaning without knowing if the electrodes are needle points, 1cm spheres,
etc. and the real distance. There are good charts in older CRC books that
list all this out. I will list needle point values here at Standard
Temperature and Pressure from that book.
Voltage Arc length in CM at STP for needle points.
0kV 0.00 :-)
5kV 0.42
10kV 0.85
15kV 1.30
20kV 1.75
25kV 2.20
30kV 2.69
35kV 3.20
40kV 3.81
45kV 4.49
50kV 5.20
If you use electrodes of a different shape (like a spark plug) these
numbers can change drastically!
I hope this has been part of the solution and not part of the problem...
:-)) - Terry >>>>