Modeling a magnifier
From: Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent: Saturday, February 21, 1998 10:13 PM
To: Tesla List
Subject: Re: Modeling a magnifier
> From: Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> Sent: Friday, February 20, 1998 4:41 PM
> To: Tesla List
> Subject: Modeling a magnifier
This is terrific. Antonio wrote:
> I was studying how to model a Tesla magnifier, and would like to hear
> comments on my reasoning:
Spotlights, camera one, closup shot in 3,2,1...
> The higher coupling coefficient in the magnifier transformer is only a
> consequence of the splitting of the secondary coil. The actual coupling
> coefficient, considering the transformer and the third coil, is as low
> as in a conventional coil.
Applause sign, studio audience applause, fanfare!
Camera one fade to black, camera two go wide on 3,2,1...
> And this is more polemic:
> The dynamic behavior of the magnifier system is practically identical to the
> one of a conventional coil (with that model, exactly), and so there is no need
> for different operating frequencies and special spark gaps (as I see commented
> in several places).
> The advantages of the magnifier are that the high voltage terminal can
> be moved away from the primary circuit, and that a more compact and predictable
> primary circuit can be used.
Applause sign, studio audience applause, fanfare! Roll commercial in
> What do you think?
> Antonio Carlos M. de Queiroz
I think that's a 'wrap' as they say in showbiz. I'm very glad to see
someone else out there who visualizes the operation of a magnifier
exactly the same way as I do! I agree with you that you have no
higher effective K in a maggy than you can achieve in a classical
design for the exact reason you indicated!
BUT, given that HV resonator K factors to the primary are the same then
in maggy systems as classical two coil systems, how can we explain
the benefits apparently seen by the magnifier experts on this list by
employing super short rotary break dwell times. At first blush the
traditional explanation has always been by saying you have much higher K, so
the energy transfers in shorter time, so you have to put out the fire in the gap
quicker. But I think Carlos has correctly pointed out that the K to
what we must in my opinion call "the high voltage resonator" no matter how you
slice it, is in fact NOT HIGHER. The normal method of measuring K in
a maggy is to only measure the coupling coefficient seen between the
primary and the segment of the HV resonator that is magnetically
coupled to that primary. I believe this technique to be erronious
and misleading. Not that this number isn't an important
specification of such a system, but the conventional K to total HV
resonator spec should also be measured , recorded and considered as
important as well.
Just a related point. If you take a classical Tesla coil and start
unwinding the secondary from the top down, stopping at intervals to
make K measurements, you will find your K factor increasing steadily as you
remove wire, until most of the secondary has been removed, then the
trend will reverse itself as you continue to remove the last of the
secondary. That point where the K has maxed out represents the right turns
ratio and coil geometry IMO for a good maggy driver coil, if you are
going to use that partially unwound coil. Chances are you will want
to rewind a new one with heavier wire. This changes the TPI figure
and the geometry and there you are back to experimenting again.
Maybe the unwashed masses representing the classical croud among us should
try rotary gaps that quench in tens of microseconds rather than the hundreds of
microseconds which is normal on most of our classical coils.
Certainly the multi-swept gaps of the maggys perform the
function of putting out the fire quickly by virtue of increasing the
approach and departure velocities of the electrodes greatly over
simpler 2 or 4 gap rotary designs. Could the extra trouble
involved in the manufacture of such superior quenching, shorter dwell gaps lead
to better operation of classical coils if employed? I have to admit
that I haven't 'dwelled' too much on such details through experimantation in
actual hardware yet. One correlation I think I have made however is that shorter
gap dwell times seem to allow a classical system to support a more massive
I expect an intelectual firestorm may result from this topic. Flames
or positive critisizm welcomed.
Robert W. Stephens
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel: 1-519-925-1771 Fax:
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