Re: New SSTC and topology in need of review

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Jimmy,
           I confess to having some difficulty following some of the
concepts expressed in your piece:

On 14 Dec 2003, at 19:45, Tesla list wrote:

 > Original poster: jimmy hynes <chunkyboy86-at-yahoo-dot-com>
 >
 > Hi,
 >
 > Gary's SSTC was impressive, and higher voltages were needed for his
 > design. In his design, the secondary was directly driven without any
 > primary coil, so to get a good impedance match, he needed high
 > voltages. If you use a primary coil, you should be able to just reduce
 > the amount of turns to get the impedance match. I believe his coil
 > worked well because of the high peak power, and not the high drive
 > voltage. I don't know enough about Dan's system to comment on it.

To get power into the base of a resonator does require a high voltage
feed as it is typically on the order of 50 Ohms unloaded. Using a
primary gets around this limitation and the higher the step-up ratio,
the more power you can get in.

 > The magnetizing current should go down, but it goes through more
 > MOSFETs in series, so it should cancel out there. The magnetizing VA
 > should be the the same compared to the real VA also. Magnetizing
 > current is not only bad for conduction loss, but it also introduces
 > switching loss that would be otherwise very small :-(. An easier way
 > to do it would be to use a resonant capacitor in series. You can get
 > impedance matches easier, no magnetizing current, and your high
 > voltage (across the primary). High coupling would no longer be needed
 > either.

Are we talking about air-cored coils? The concept of magnetizing
current doesn't really apply in that case.

 > I don't understand why the current would skyrocket. How much does it
 > increase? At half the turns, I would expect about 4 the current,
 > depending on the streamer load. Is it significantly different? Do the
 > sparks seem brighter? The only thing I can think of is that the
 > effective coupling goes down due to stray inductance leading to the
 > primary, but that shouldn't be significant until down around 1 or 2
 > turns. Can you think of an explanation?

You can see the dramatic effects of reducing primary turns at quite
low powers (a few W) with a resonator, primary and lo-Z o/p signal
generator and scope (and fluoro tube if one is handy). Reducing the
primary turns causes the output to climb dramatically and it is not
related to the reactance of the primary as shown by tuning the
generator around the resonant frequency. Doing this also sucks a lot
of current out of the generator.

Malcolm

 > Wait a minute... I now remember someone (Dan Mccauley?) found the
 > resonator to look like a current sink. That means that if you cut the
 > turns in half, you get 4x the magnetizing current, but twice the in
 > phase current. That could be it. In that case, I think you would just
 > need a lower impedance resonator. If what I said is right, then it
 > isn't that you need at leat 5 turns, it's that the resonator doesn's
 > want more power. The same thing should happen at 20 turns if you do a
 > four stage circuit like yours. Make sense to anyone?
 >
 > There may be more to it, but I think the flyback works better because
 > there is less current flowing through the same MOSFETs, and it is more
 > efficient. The more MOSFETs in series should remove this benefit :-(
 >
 > It sounds like a cool project, and we'll see if higher voltages do
 > help. Good luck!
 >
 > --- Tesla list <tesla-at-pupman-dot-com> wrote:
 >  > Original poster: "Steven Ward" <srward16-at-hotmail-dot-com>
 >  >
 >  > Well Jimmy, im not entirely sure what i am going to gain, but i at
 >  least > *think* it should be worthwhile.  Dan McCauley mentioned that
 >  his MOT SSTC > (when working quite a while ago now) produced
 >  extremely long sparks.  Also, > Dr. Gary Johnson has a large SSTC
 >  running 1700VDC into a half-bridge.. his > coil makes some 54" sparks
 >  if i remember, though it IS powered from a PT. > > Basically, my
 >  thought is that magnetizing current could be reduced a bit, > and i
 >  can more easily get an impedance match that would give lots of power
 >  > throughput without half of the current going to Imag.  With my 170V
 >  SSTCs > ive gotten down to 5 turn primaries that are some 8" tall.
 >  Very tight > coupling and very few turns.  But, each turn taken off
 >  makes the current > input skyrocket but does very little to increase
 >  spark length.  It just > SEEMS that you need higher voltages.  As to
 >  how high, i dont know, but > 1400V seemed like a *fun* place to
 >  begin. > > I must also note how my half-bridge flyback driver reacts
 >  with low > voltage/high current (few primary turns) power supplies
 >  and high > voltage/low current (many primary turns).  At low voltages
 >  the flyback has > several resonant frequencies and makes decent
 >  sparks (with some > heating).  But, at 120V input, i get
 >  disasterously long sparks but only 1 > Fres, and with no heating of
 >  components at all.  I know we are talking > about 2 completely
 >  different things here, but i dont see why this concept > would not
 >  hold up with SSTCs. > > Steve Ward > > > > > >From: "Tesla list"
 >  <tesla-at-pupman-dot-com> > >To: tesla-at-pupman-dot-com > >Subject: Re: New SSTC
 >  and topology in need of review > >Date: Sun, 14 Dec 2003 10:53:49
 >  -0700 > > > >Original poster: jimmy hynes <chunkyboy86-at-yahoo-dot-com> > >
 >  > >Hi, > > > >I remember seeing that circuit too, and thought it was
 >  pretty cool. What > >do you expect to gain > >from a higher input
 >  voltage? The only thing I can see is the increased > >number of
 >  primary turns > >needed for an impedance match. Unless you are using
 >  1 turn on normal > >SSTCs, I don't see the > >benefit. > > > >---
 >  Tesla list <tesla-at-pupman-dot-com> wrote: > > > Original poster: "Steven
 >  Ward" <srward16-at-hotmail-dot-com> > > > > > > Hi everyone, > > > > > > I
 >  have been working out my latest SSTC designed in the hopes that
 >  higher > > > voltage across the primary coil will work better than
 >  typical low
 > voltages
 >  > > > of some 170-340V.  This new design should be able to produce
 >  about 1400V > > > across the primary in a very unique way: > > > > >
 >  > http://www.hot-streamer-dot-com/srward16/SSSSTC.htm > > > > > > Ive
 >  been studying this topology for a long time now and im in the
 > process
 >  > > > of building this thing because i just have to see it for
 >  myself. > >Basically > > > i would like for you guys to analyze this
 >  topology and give me some > > > feedback on potential
 >  problems/benefits i may see.  I look forward
 > to what
 >  > > > the solid state experts say.  Maybe this will lead to a new
 >  avenue
 > in solid
 >  > > > state tesla coiling... though i have a feeling many would not
 >  like to > > > reproduce a 16 fet design (or 32 fets if things go well
 >  :O). > > > > > > So lets hear it! what do you all think? > > > > > >
 >  Thanks, > > > > > > Steve Ward > > > > > > > > > > > >===== > >Jimmy
 >  > > > >
 >
 >
 > =====
 > Jimmy
 >
 >
 >