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magnifier tests/comparisons (magnifier modeling)
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From: Antonio C. M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
Sent: Friday, March 13, 1998 12:41 PM
To: Tesla List
Subject: Re: magnifier tests/comparisons (magnifier modeling)
John Freau wrote:
> First I set up a small classic TC using k ~ .18, I observed the beat
> period to be about 11uS which is about right for the 510kHz coil. Max
> spark length was about 3" - 4". Pri L ~ 85uH, sec L = 13mH, C = .0015uF,
> 4 gap series quench sync rotary, powered by 10kV, 23ma OBIT. Pri
> tapped at 19 turns. Quenching was poor at around the 3rd or 4th beat
> notch.
Analyzing this setup, without losses, assuming 10 kV input I obtained:
Considering the secondary resonating at the same frequency of the
primary (446 kHz), C2=9.81 pF, beating period=12.2 us, and V2max=122 kV.
Considering the secondary resonating at 510 kHz (slightly out of tune),
C2=7.49 pF, beating period=9.2 us, and V2max=112 kV.
> Next the secondary was moved off to the side to form an extra coil,
> and a new 1.5mH secondary was installed at k = .34. The magnifier
> primary tap point was left at 19 turns, and the beat period was
> observed to be 17uS, which equates to an effective k of around .11.
> Ringdown freq was about 500kHz. Quenching was much better at
> around the 2nd or 3rd beat notch in magnifier mode. Spark length
> was about the same.
This would result in an equivalent two-coil system with L2=13+1.5=14.5 mH
and k=0.34*sqrt(1.5/(13+1.5))=0.11.
With C3=9.81 pF this results in a beating period of 18.6 us and
V3max=109 kV.
With C3=7.49 pF, the beating period is 16.1 us, and V3max=114 kV.
> Next the system was set up again as a classic coil at k = .11. The
> beat period was about 17uS, and the quenching was greatly improved,
> (2nd notch), perhaps better than the magnifier. Spark length was still
> the same.
The quenching difference may be caused by slightly imperfect tuning, what
leaves some energy in the primary.
> 1. The effective coupling of a magnifier is relatively loose, and is
> is much lower than the measured k of the driver alone.
If L2<<L3 I think that this is really the only possibility, excluding
pseudo-CW operation and the use of a huge C2 capacitance.
> 2. This loose coupling makes a magnifier relatively easy to quench,
> but it may be a little harder to quench for the same "effective k"
> compared with a classic coil (more tests needed here). In any case,
> the magnifier with a k = .34 driver, was much easier to quench than
> the classic TC at k = .18.
Good quenching requires little primary energy, and so good tuning,
and long beating period to allow more time for the cooling of the gap
and dissipation of the ion channel. I think.
> 3. The above results explain why spark gaps can quench a maggy
> that uses a k = .4 to k = .6 driver, whereas a classic coil with such
> a tight coupling cannot be quenched adequately.
Agreed.
> 4. Spark output was about the same, classic TC vs, magnifier.
The relation Voutmax<Vinmax*sqrt(Cin/Cout) is the same for both
configurations. The 3"-4" sparks are consistent with a little more
than 100 kV.
> I intend to increase the coupling of the driver to k = .4 to .6 and
> measure the resulting effective coupling based on the observed
> beat period.
I would like to see what happens when L2 and L3 are of similar sizes.
This would keep the effective k high, C2 would not be negligible, and
the operation of the system may be more complex.
These are very useful experiments, and show the right way to go for
the understanding of precisely how these devices work.
Antonio Carlos M. de Queiroz
http://www.coe.ufrj.br/~acmq