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Re: Tank Capacitance: what is the limit

Subject:  Re: Tank Capacitance: what is the limit
  Date:   Mon, 5 May 1997 16:19:49 -0400
  From:   "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To:  "Tesla List" <tesla-at-pupman-dot-com>


Barry, Malcolm, All,
Barry, your question is basic and fundamental. While I agree
wholeheartedly with Malcolm's comments about increasing primary
inductance and increasing Q, I also have to state that when push
comes to shove that it is the CAPACITOR and not the primary coil that
is responsible for the initial energy that will eventually be
sloshing around in the primary circuit. Or to put it another way, we
coilers charge up the dumb old capacitor and then dump as much of
that energy as we can into the game (which begins in earnest when the
old spark gap fires). We can talk about relative power losses, but
let's not lose sight of the fact that we wouldn't have ANY power to
lose in the first place if it weren't for that there stuff that's
stored up in the old dielectric! You can't get any power out that you
don't first put in. (Sorry if I have offended anyone's deeply held
religious beliefs here). Making the primary larger will improve the
Q, but all the Q in the world won't help you if you don't have energy
getting INTO the circuit in the first place. The question is "When is
more too much?"

There are several ways you can increase the *INPUT* energy. I am
referring here to USEABLE energy. Shorting out the transformer
secondary, for example, would increase the energy CONSUMED, but in a
very unhelpful way. Let's look only at increasing useful input
energy.

1) You can increase the value of the capacitance.
2) You can increase the voltage applied to the capacitance.
3) You can play with the REPETITION RATE at which the capacitor is
charged/discharged. (Break Rate, Spark Gap Length, and all that kind
of stuff).

Increasing the capacitance (and keeping charging voltage the same)
obviously affects the tuning and the Q, because C has changed.
Current drawn from the transformer is increased. Current limited
transformers obviously have their limits. Losses will increase, but
so will total power DELIVERED. The question is where is the
break-even point? It varies for each experimental set up. But there
are definitely minimum and maximum limits that we can mathematize in
general terms.

Increasing the voltage is particularly effective because power is
related to E^2/R. This probably gives us the most bang for the buck
improvement, and has the nice side effect of (theoretically at least)
not changing the resonant tune. L and C remain the same. (But in the
real world you almost always have to tweak the silly circuit to wring
the optimum performance out of it). You may have the same value
capacitor, but past a certain point you had better use one rated at a
higher voltage!

Playing around with the Spark Gap spacing and Break Rate allow us to
basically keep the same tune (some tweaking desireable in the real
world), but optimize the size and spacing of the packets of energy
that we dump into the circuit. A little thought here will tell us
that both the size of the packet and its spacing will influence the
amplitude and other factors affecting the resonant ring down of the
primary circuit.

All of these together, plus a whole bunch of other subtle things (too
numerous to mention) conspire together to play games with the total
system. When we get just the right mixture of This and That, we
achieve that wonderful thing we call synergy, and we get the most
bang for the buck in the form of wonderful arcs (sparks) (discharges)
(plasma) (those long snakey things we all love to see, no matter what
we choose to call 'em!)

Hope these ramblings help someone.

Fr. Tom McGahee