Re: OLTC Maggy modelling

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "boris petkovic by way of Terry Fritz <teslalist-at-qwest-dot-net>" <petkovic7-at-yahoo-dot-com>

Hi Steve,

 > :D so I decided to put together a model. I
 > basically did a model of
 > what I would build:
 >
 > http://www.scopeboy-dot-com/tesla/mag-nette.jpg
 >
 > This is a (2,3,4) magnifier based on the same
 > resonator, IGBTs and tank
 > capacitor used in my original OLTC. Thus it has the
 > same bang energy and
 > output voltage.
---
It is good you decided for (2,3,4) instead of (1,2,3).
I disliked (1,2,3) from the first moment.
I was only waiting the moment when you'  figure out
why  was (2,3,4) constructively much less
problematic.Apart from voltage and other mentioned
problems,It is also a capacity C2 thing ,particulary
in your  case since since small C3~11 pf.
For 1,2,3 for optimisation you need about C2~25pf and
K~0.67.In attempt to constructively get K=0.67 with 2
turn primary closely placed to secondary turns it's
all the chance that you exceed C2=25 pf -higher than
optimum and it would be a serious drawback in process
of optimisation.
C2 partialy realised in OLTC design,between 2 coils,
with C1 big cap and small L1 in 2,3,4 mode can be just
of benefit.
Note,that when I discussed interferrence in previous
posts,it was related to usually built spark gap mag.'s
  so bellowed contruction  with much higher surge
impedances of primary circuit and smaller C1 (like
0.015 uf in Bert's magnifier),and high BPS.Even
then,if C2  was mostly realsed  through capacity
between 2 coils   these systems would work fine since
the advantage of smaller primary circuit looses
would more than compensate interference.
---



 > If the IGBT were a perfect switch that could hold
 > off voltage in both
 > directions, the result would be this:
 >
 > http://www.scopeboy-dot-com/tesla/mg_no_diode.jpg
 >
 > Which is exactly what we want! Unfortunately, doing
 > this in real life
 > requires two IGBTs in series, each with a diode in
 > series. That's four bits
 > of silicon in series, thus about three times the
 > cost, and roughly six
 > times the losses of a single IGBT carrying the same
 > current.
---
Bummer.. I admit I didn't give a thought to that.
You think there isn't primary circuit way to prevent
this (except getting "IGBT bricks")?
---

 >
 > This would more than offset the efficiency advantage
 > due to the quicker
 > energy transfer, and the maggy's slightly lower
 > primary current (750A pk
 > vs. 800 for the 2-coil.) And, efficiency advantage
 > was the only reason for
 > preferring the maggy in the first place. (Unless its
 > fast rise time has
 > magical streamer-growing properties or something.)
 >
 > My conclusion is that a 2-coil OLTC will give much
 > more bang for the buck
 > spent on silicon than a 3-coil one. Unless anyone
 > can persuade me otherwise?
---
Can you first notch quench your 2-coil OLTC
configuration with K=0.2?

regards,
Boris

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