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Re: Weather/coil performance

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

Hi Jared and all,

My 10" coil always performed significantly better on cold dry days than humid ones, with longer streamers and easier initial breakout. Maximum streamer length was reduced by 6 - 8" versus identical operation in dry air. Initial breakout was also more difficult (a higher Variac setting was required). High humidity apparently increased the initial breakout voltage while significantly shortening the streamers once breakout was achieved.

There is other empirical evidence that humidity has a significant negative effect on positive streamer length. Like oxygen, water vapor is a very electronegative gas. Water vapor captures free electrons, prematurely removing them from further participation in the avalanche processes that are critical for streamer formation and growth.

Higher rates of electron capture result in a significantly higher electrical field being required to support streamer growth in humid air versus dry. Experimental evidence in the literature suggests high humidity causes a slight increase (~5%) in the initial breakdown voltage, as well as having a major inhibiting impact on streamer propagation (Loeb, "Electrical Coronas", pp 225-227). Subsequent research done by Phelps and Griffiths ("Dependence of Positive Corona Streamer Propagation on Air Pressure and Water Vapor Content During Times of Higher Humidity", Journal of Applied Physics 47, 2929 (1976)) confirms and further quantifies these effects.


Tesla list wrote:
Original poster: "Jared Dwarshuis" <jdwarshuis@xxxxxxxxx>
Hi: Jay
Temperature, humidity and barometric pressure will have little
effect, must be something else. Perhaps your ground connection needs
attention. Are you using a breakout point?
I assume that you are using an NST...........
Get to know the sound that your spark gap makes when it is working
well. When the spark gap starts sounding like a sick bumblbee then
you are not quenching properly and gap adjustment will be needed. It
is also possible to have a gap that is not quenching because of bad
primary tuning, then of course gap adjustment will not cure the
My guess is that you have found the right primary tap point; that
your gap needs adjustment. Beware, large gap settings place heavy
loads on NST, and they are rather fragile.
Sincerely: Jared Dwarshuis