Re: TESLA COIL REVISED

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

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

"It is important to distinguish between two quite different modes of
operation of the TC:

1) The cap discharge type, in which the primary cap acts as a power
compression circuit;

2) The CW drive, in which there is no power compression and energy
is stored/accumulated in the resonant secondary.

(In both cases a kind of 'resonant rise' is involved, but the term
is too vague to be of much use in discussion).

In case (1) the output voltage is at most sqrt(Lp/Ls) or sqrt(Cp/Cs)
times the input voltage, and is reduced only a little by poor Q
factor due to (a) and (b) above.  Transfer of the compressed power
through the TC is very quick - only taking a few or several RF
cycles, and as a result there is time only for a few percent of the
input energy to dissipate in the secondary coil loss.  Increasing
secondary Q from say 50 to 500 would only make a few percent
increase in output voltage.  As the Q factor approaches infinity,
the output tends, not to infinity, but to Vin * sqrt(Cp/Cs), etc,
because only a finite quantity of energy is injected into the coil
with each cap discharge."

	I (and probably others here) have run simulations where I varied the Q
and looked at the maximum secondary voltage.  If the coupling is
reasonably tight, everything is in tune, and the quenching is "at a
notch", Q's as low as 20 result in a peak voltage loss of only a few
percent.  If the quenching is wrong the loss can be greater.  This is a
simplified simulation without breakout.  In the case where breakout
occurs (and that's what we all want - long streamers) the Q is probably
even less important.  Conventional wisdom says very high Q is better.
That's for sure good for the soul but fact is that series gap resistance
in the primary and shunt streamer impedance in the secondary are the
real limiting factors.

	I've never run any experiments where I varied the Q (kind of hard to do
unless you want to wind a bunch of coils and I don't) but I strongly
suspect that unloaded Q's over 100 are entirely unnecessary.

Ed

Ed