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BIPOLAR COIL

 * Carbons Sent to: usa-tesla-at-usa-dot-net

Quoting P.L.Mason-at-bath.ac.uk:

> If you build a centre driven coil, and cause the discharges to
> arc between the opposite ends of the coil, then a) How many 
> turns should the secondary have - still 800-1000 (in line
> with RQ's recommendations) or double this?

These coils are more properly called "bipolar" Tesla coils. They
produce two 1/4 wave peaks, one at either end. These coils
operate at a frequency that is double the normal 1/4 wave
frequency.

Because the nul voltage point occurs in the middle of the
winding, the coil parameters need to be changed a bit to achieve
the best performance. Longer coils with a higher aspect ratio
work best. I have found that the "candle stick" coils from my
early efforts that were rather poor performers in 1/4 wave work,
made excellent bipolar coils when orientated sideways with a
primary placed around the middle. The best results that I have
obtained (I have done some experimentation with these config-
urations, but not exhaustive by any means) were with coils that
had about 1500 - 1800 turns and aspect ratios of about 7. 

> b) Or can you just pretend that it is a standard base driven 
> coil, (designed as such) with the primary coil in a different 
> place and no RF ground? 

Not really, because that is not what is going on. A coil built
for 1/4 wave work tends to couple too tightly when used as a
bipolar coil. The primary must be completely redesigned to couple
a 1/4 wave designed coil for bipolar firing, and even then lots
of insulation must be placed between the two coils to prevent the
secondary from striking back to the primary.

Richard Quick


... If all else fails... Throw another megavolt across it!
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