Re: OLTC Multi Primary

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

Original poster: "Marry Krutsch by way of Terry Fritz <twftesla-at-qwest-dot-net>" <u236-at-earthlink-dot-net>

Hi All,

	I don't know whether or not the drawing/idea was mis-understood or not,
but I'll explain the idea again.  I discussed this with Terry a few
weeks ago, and he thought that it was too complicated.  I still don't
think so, but then again, I'm not the one trying to build it and get it
to work without smoke entering the picture ;-)).  I also don't have the
fancy computer modeling stuff that Terry has (I can't even imagine how
much that aids in designing circuits).

	Anyway, the idea was not only for each transistor to have its own
capacitor, but for each one to have its own complete tank circuit,
identical to the others.  The main point to this was keeping the
resonant frequency in the "normal" TC range by keeping the Fres of each
tank high, while keeping the total energy in all of the caps (tanks)
high enough to do some good at low (120 BPS) break rates.  That way, the
secondary coil wouldn't need to have 0.5 Henries of inductance =:-0, and
would therefor be less of a pain to build.

	Also, using this method, power-per-break can be increased without
further lowering the operating frequency, if the coil is running
directly from the line and not DC.  The current consensus (I think) is
that the prototype OLTC will run on DC.

	The idea was to wind all the "separate" primary coils into a bundle,
like Litz wire, so that no one tank would see too much more kickback
than the others, and so the secondary coil would "see" only one
primary.  Running at such a low frequency means that, using a
"conventional" TC tank setup, you must lose either primary inductance,
or capacitance.  Each one has its inherant problems.  The multiple tank
circuit method allows you to in effect, lose neither one.  I know that
an IGBT is a little different from a sparkgap ;-)), but their function
in the circuit is the same.

	Current sharing is less of a problem, since there are no transistors in
parallel.  The firing timing issue is the same as with the current
setup.  And, a problem with one circuit should not affect the others, so
a catastophic "dominoe effect" failure would be less likely.  The wire
used in each tank would be much smaller than that used in a single
larger one, so making and manipulating the setup would be easier.  There
were some other perks to this (I think), but I've forgotten them.

	I did some math, and worked out a coil that runs at 70kHz, with a TOTAL
primary capacitance of 30uF.  It has 10 tanks, each with a 3uF cap, and
a 1.75 turn, 4.5" radius, 1.72 uH primary.  The total energy stored at a
peak voltage of 320 is 1.56 joules.  The primary would in reality be 1
turn.  The extra 0.75 is to account for off-axis inductance (tank
wiring), and other stray effects.  If anything, this should be lower. 
The secondary is 27.5" (wound), 2175 turns, and 6" in diameter.  The
toroid is a modest 6" by 20".

	Lastly, I should say that I'm sure that there are problems with this
idea that I can't see, since I'm not know for my intelligence ;-)).  So,
I invite the gurus of TC'ing to pick this clean.  I know I'll learn
something from that.  I also don't mean to question Terry's judgement. 
I wouldn't have mentioned this idea on the list, but since someone
brought it up, I though I'd explain it.  Terry is right in keeping
things simple for the first try.  This can be explored later (if at
all).  I left some stuff out, but I'm getting tired (it's 12:45 am, and
I've got work tomorrow).  

	Sorry for such a long post.  I didn't intend for it to be that way
;-)).  Thanks for reading,
Winston K.


Tesla list wrote:
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Jonathon,
> 
> At 10:49 AM 8/13/2002 -0400, you wrote:
> >Hello everyone, esp. those on the OLTC scene...
> >
> >Looking through hot-streamer-dot-com/temp, whatever happened to the Multi
primary
> >idea?
> >(hot-streamer-dot-com/temp/OLTC_Multi_Primary.jpg)
> >Too much coupling? Too Complicated, or too many priamry coils ( > 10 )
> 
> It just seems too complex and ten primary loops may reduce the inductance
> of the primary too much.  "I" also worry that the voltages on each loop may
> not stay in sync with each other.  It just had a few unknowns and no real
> reason to go that way.  I am trying to keep everything as basic and simple
> as possible, pleanty of time later to make things complicated ;-))
> 
> Cheers,
> 
>         Terry
> 
> >
> >I think having each IGBT with its own cap is a great idea, i would have
never
> >thought of that!
> >
> >Keep up the good work!  Hot-streamer-dot-com/OLTC now exists, but is under
> >construction.
> >
> >---------------------------------------
> >Jonathon Reinhart
> >hot-streamer-dot-com/jonathon
> >