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Re: TC Output Voltage
Tesla List wrote:
>
> >From MALCOLM-at-directorate.wnp.ac.nzSun Nov 3 22:48:21 1996
> Date: Mon, 4 Nov 1996 12:50:24 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: TC Output Voltage
>
> Hi everyone,
> I think I have figured out a way to measure output
> voltage indirectly (at least using lumped circuit values). Since
> we can measure the primary directly, we can observe the amplitude
> of two successive beat envelopes. The ring-down, ring-back-up of the
> primary will show a drop in amplitude due to losses and if the
> system is prevented from breaking out into sparks, spark losses are
> excluded from these losses. Using the difference in successive peak
> primary amplitudes, we can deduce system Q and compare that with
> theoretical calcs. We can also make a good estimate of the losses
> over one half of a beat hump and thereby quantify how much energy
> went to the secondary first time round, also how much arrived back
> at the primary. These are a couple of random thoughts. I would
> appreciate anyone else who can contribute to this doing so with
> out relegating it to pooh-pooh status. If anyone cares to, the VSWR
> view of things could also be used to calculate Vsec, bearing in mind
> that the helix is topped by a lumped capacitance and that secondary
> current with a top hat is considerably more uniform than that you
> would find in a pure helical resonator.
> A friend of mine who is an RF engineer has examined some
> structures and come to the conclusion that a low Zo is required in
> the secondary. That is, a low L/C ratio in the helix itself. That runs
> completely counter to what we actually do in these machines (Lo
> Zprim, Hi Zsec) with Zsec dragged down by a lumped topload. As a
> result, I have suggested that antenna theory is not really applicable
> to what we are trying to do with our coils. Antennas are of course
> designed to radiate prodigiously whereas we are ideally after none at
> all (v. high radiation resistance).
>
> Any thoughts on the above would be appreciated.
> Malcolm
Malcolm and all,
The argument you present sounds like a good one. The only problem I see
is that this approach, alone, doesn't reflect high efficiency operation
of the coil (i.e., quenched at/near the end of the first beat). With no
quenching, a sizable portion of the secondary's energy is being
transferred back to the primary instead of being fully dissipated in
streamers. Since streamer loading is a non-linear function of power
output, this may not give us as good a measure of efficiency as when
running under more ideal (quenched) condition. However, your approach
may be combined with secondary Q measurements to give us the complete
answer.
Without breakout, we have very high secondary Q. Under these
conditions, the rate of system energy loss will be mostly governed by
primary/gap losses. Although we may not be able to directly measure the
maximum energy stored in the secondary at the end of the first beat, we
can measure the amount of energy we get back in the primary circuit at
the end of the second beat. As you suggest, this should allow us to
compute the maximum amount of energy we must have had in the secondary
at the end of the first beat, and therefore the maximum voltage.
Richard's proposal to simultaneously measure primary voltage and current
and compute instantaeous energy is excellent in that it doesn't force us
to use only the max voltage or current points to estimate points of
maximum primary energy...
We can remotely measure the secondary voltage waveforms under properly
quenched conditions, and calculate the secondary Q's with/without
breakout while properly quenching the gap at the end of the first beat.
This should allow us to remove the portion of energy loss coming from
the secondary only (with no breakout) from the total losses (secondary
and streamers). Since we've previously estimated of the maximum energy
transferred to the secondary per bang, we can now compute the average
energy lost to the streamers per bang. Multiply the per-bang energy loss
by the number of bangs/second, and we get an estimate of the average
power being dissipated in the streamers. Some more thought is needed
here... but I think we may be on the right track to solving this....
Your second observation is an interesting one - antenna theory applies
in
an opposite sense to the way most RF engineers would look at it. You're
absolutely correct: we want to make the lousiest antenna possible,
ideally with an infinate VSWR. We want to maximize sparks as output, not
EM radiation. By heavily top-loading, and running only near the natural
resonant frequency, we approach the expected behavior of a high Q,
inductively coupled, series LC circuit, and can avoid most of the nasty
complexities of helical resonator and antenna theory...
Safe coilin' to ya, Malcolm!
-- Bert --