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magnifier vs. classic tc (magnifier modeling)
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From: Antonio C. M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
Sent: Sunday, March 22, 1998 12:58 AM
To: Tesla List
Subject: Re: magnifier vs. classic tc (magnifier modeling)
John Freau wrote:
> I've added more C2 as suggested by Antonio, by installing one of
> Lou Balint's variable tune caps across the secondary coil. This gives
> me a cap range of 38pF to 164pF (and maybe more).
>
> I used the 1.5mH secondary with the 11.2mH extra coil to try to keep
> the voltage across the cap limited to reasonable levels. I left the pri
> tap at the same point (turn #19) that I used before without the tune
> cap. A 1 1/2" by 5" toroid was used with a sharp point on top. The
> strongest sparks occured using the full 164 pF. (The cap can be
> set up to give more than 164pF, but it's voltage capability then drops
> to half...so it may arc internally...I didn't try it).
If the 11.2 mH is your 510 kHz coil, this system is something as:
L2 = 1.5 mH; C2 = 8 pF + Cconnections + Cvariable
L3 = 11.2 mH; C3 = 8.7 pF + 7.1 pF = 15.8 pF.
The condition C2L2=C3(L2+L3) gives C2=134 pF, that is in the range of
your variable capacitor.
> I can see strong beating effects in the after-quench ringdown
> waveform on the scope. This beating changes drastically as I
> adjust the variable tune cap. The beat period can be made long or short,
> by adjustment of the tune cap.
This is expected. The voltage at the top of the third coil always
shall present beats (if C2 is significant), with variated appearance and
generally mixed with higher-order resonances, what can turn the
observation difficult (how are you observing the waveforms?).
The best tuning is obtained when perfect beats are obtained at the
top of the secondary coil (or anywhere as currents/voltages in L2/C2).
At this point waveforms shall appear much cleaner, due to the filtering
action of L2C2.
For your values, the best post-quench beat period would be the one
corresponding to k'=sqrt(L2/(L2+L3))=0.34. (this k' is unrelated to
the k of the L1L2 transformer). Measured at the top of L2.
I could confirm these relations with great accuracy in my low-power
tests.
> The beats before the quench are 7uS
> long when the variable cap is tuned for best spark *without* the sharp
> point. This suggests an effective coupling of k = .28 or so, which
> represents a significant tightening from the earlier *no cap* tests,
> which showed a k = .18 effective coupling (but...see below).
Expected. The system tends to behave as a two-coil system.
> This
> tune point also corresponds to the formation of *well formed* beats.
> The tune cap has to be readjusted (to 38pF [minimum cap]) for best
> spark when the point is added to the top of the toroid. When this
> point is added, and the cap tuned for best spark, the beats blur
> together. Maybe when the point is not in place, delayed streamer
> breakout permits stronger beating to occur between the secondary
> and the extra coil before breakout.
The point (sparking) adds strong nonlinearity in the system, and the
linear model may go away...
> In one case, the RF formed what looked like a beat that was
> 34uS long which would imply an effective k = .06. Calc. is about
> k = .14. In still another test, the beat period seemed to be 24uS,
> but in both cases, there were visible beats within the main beats.
> So the effective k depends on which beats you look at.
This is before or after quenching? With significant C2 the system
oscillates at three different frequencies, not counting harmonics,
and the waveforms become very confuse before quenching. I don't
know what would be the ideal tuning before quenching. Probably
some condition resulting in long beats at the primary circuit, if
possible.
> When the
> point is installed on the toroid, then the RF rings down lower and
> lower as each beat occurs. But when the point is not installed, the
> RF rings up over a number of beats, then down over a number of
> beats. This is what gives the appearance of one long modulated
> beat (and there are a number of these large ones too, these long
> beats ring only down from beat to beat, never up).
After or before quenching? An increase of beat amplitude after the
quenching is something unexpected.
> Regarding the effective k = .28 above however (no point on toroid),
> it would seem to me that the energy might not be fully transfered
> during these beats, these may be false *pseudo-beats*. I have to
> look at this again.
Consider only beats measured over L2 or C2. The voltage at the top
of L3 includes high-order resonances.
> I also tried tuning the primary at turn # 20, results were a little
> different, but I have to recheck this. The only other tune point I
> tried was around turn # 24, but no sparks were obtained. The
> variable tune cap doesn't seem to affect the overall frequency very
> much. But tuning of the variable cap was very critical in all these
> tests. I didn't recheck to verify that Fo was somewhere around
> 500kHz.
This is expected. But C2 controls how much of the primary energy goes
to the secondary end, and how this energy is transferred to C3.
> Some variable cap adjustments resulted in a modulated appearance
> in the sense that two beats would be strong, then two were weak,
> then two were of intermediate height, then two were weaker yet, etc.
Expected, from the combination of three sinusoids at different
frequencies.
> I also ran the coil without the variable tune cap, and I can see that
> the beats *are* occuring after the quench even with the small self C
> of the secondary (or it certainly looked that way). The spark output
> is a little weaker without the variable cap, but tuning is probably not
> as precise. Without the variable cap, the beats were about 10uS.
Expected. But as I said above, the voltage at the top terminal (C3) is
very complicated due to high-order resonances. Verify what happens at
the top of L2.
> I may try using the 5.75mH secondary coil, but oil breakdown may
> occur in the variable cap.
> More work is needed.
Ok. Going step by step, I believe that an accurate figure of what the
magnifier does can be derived.
Antonio Carlos M. de Queiroz
http://www.coe.ufrj.br/~acmq