RE: Win tesla

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Sphere gap breakdown is not a linear function of distance unless the 
distance is very much shorter than the diameter of the sphere (so you 
approximate a uniform field)..

In a uniform field gap, breakdown is around 70 kV/inch

In a gap with sharp edges/pointy wires/etc, the breakdown could be a lot 
less...

As a rule of thumb, needle gaps breakdown at roughly 1/3 the voltage of a 
sphere gap where the gap is <1/4 the sphere diameter (i.e. a 1/4" gap for 
1" spheres)  Going off the spheregap tables.. that quarter inch gap breaks 
down at around 20 kV (note, actually bigger than 1/4 of 70 kV, such are the 
inconsistencies of HV behavior).. I would expect a needle gap 1/4" long (or 
sharp edges of copper pipe, or ends of 1/4-20 bolts, etc.) to breakdown at 
8-10 kV....

But, the big thing to remember, particularly for lowish or very high 
voltages (because in both situations, the gaps designs used have 
non-uniform fields), is that spark gaps are not something you can easily 
design by rule. Empiricism truly reigns, and the exact breakdown voltage 
WILL change with everything you can imagine (temperature of air, temp of 
electrodes, humidity, phase of the moon, surface finish, dust on the 
surface, incident radiation (UV or ionizing), etc....)

Only in a carefully machined and shaped gap, carefully conditioned, 
environmentally controlled,etc. can you get consistent (as in within 5%) 
breakdown characteristics.


At 08:08 AM 10/17/2002 -0600, you wrote:
>Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><Gary.Lau-at-hp-dot-com>
>
>8400V/inch sounds too low.  From the sphere breakdown voltage chart on
>Terry's site,
>http://hot-streamer-dot-com/TeslaCoils/Misc/SGapVolt.jpg, two 2.5cm (1")
>spheres 0.58cm (0.228") apart would break down at 20kV peak.  Assuming
>voltage vs. distance is linear (which does not seem to be the case from the
>chart), that comes out to 87.7kV per inch.  Maybe a decimal place error?
>
>Gary Lau
>MA, USA
>
> >Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
><Rscopper-at-aol-dot-com>
> >
> >That WinTesla value is based on 8400 volts per inch.
> >12000/8400=1.43in
>
> >> >I've just started using the WinTesla program and I've noticed that the
>fixed
> >>> spark gap calculator is not giving the numbers that I would expect. I
>entered
> >>> 8 > gaps for a 12000 volt NST and it responded with 0.178 in/gap. This
>is far too
> >>> large.