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Re: 600kV voltmeter

Original poster: Bert Hickman <bert.hickman@xxxxxxxxxx>

Tesla list wrote:

It is a bit disappointing to discover your 4 ft. long continuous spark
shrinks to only 7 inches in the pulsed mode and gives a true output of
approx 160 kV. It's hard on the ego after you have told all your friends
your coil is running at 1/2 a million volts!!
FWIW, I had this epiphany a few months back. What happens every 10mS that makes the spark channel dissipate?
Or as Richard Hull posed, why does the streamer *go out* at all?
Why don't all streamers follow the same channel? I suppose the same goes for non-TC sparks...
-Phil LaBudde

Hi Phil,

Interesting questions. I took a shot at answering some of these on Wikipedia - go to http://en.wikipedia.org/wiki/Tesla_coil and read the "Why do Tesla Coil Sparks jump to open air?" section. Feel free to edit/change/add as appropriate... it IS a Wiki... :^)

The 10 mS thing mostly has to do with the spark channel cooling down between shots. The thinner the channel, the more rapidly it cools down. Cool air is denser and harder to "break down". This (plus space charge effects at the streamer tips) is why the streamer root seems to change only slowly, while the far ends constantly dart and change location. Space charge effects are also likely the reason why a well established discharge path may suddenly become replaced by a new path on the opposite side of the toroid.

This effect is also what limits high current spark gaps to repetition rates of ~100 Hz without external air flow/cooling. At faster rates, the gap doesn't have a chance to fully recover its dielectric strength between shots.

Best regards,

-- Bert --