Re: SISG: OLTC-ish coil design: Help?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

Thanks, Terry!  Hello again, too!  Just can't please
you with my capacitance calculations, can I? ;-))

I'll probably design down for 150W, then.  This brings
me down to about 342nF, which ought to keep me
"happily" under 600A for peak primary current if I
stick with ~4 turns on the primary, in which case I
can take a bunch of turns off the secondary, maybe
going for #28 instead while maintaining a 4:1 aspect
ratio.  That'd be cooler (literally).  Alternatively,
I could drag the primary frequency down to match the
2000-turns-of-#30 primary...JavaTC thinks that'd let
me get away with a full **five turns** on the primary
(no way!! :-)) giving me even more peak current
breathing room on the IGBTs.  Decisions, decisions!!!
Guess I'll sleep on it.  Might have to build two
primaries and try it both ways ;-)

May have to pick up one of those eBay Special IGBT
bricks some day very soon.

Best Regards,
Aaron, N7OE

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: Vardan
> <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
>
<snip>
>
> >If I fairly arbitrarily choose 2000 turns of #30
> wire
> >on a 6"x24" secondary with the 14" sphere topload,
> the
> >frequency works out to about 90kHz.  To match that
> in
> >the primary circuit, I'd need little more than four
> >turns (!) which yields little more than 6uH.  That,
> in
> >turn, suggests a peak primary current of almost
> 700A!
>
> Be a bit careful of lots of turns of thin wire.  My
> secondary Rac is
> burning almost as much heat as the IGBTs!!!
> MandK-3.1 seems to give
> the best numbers for Rac compared to my measured
> values:
>
>
http://hot-streamer.com/TeslaCoils/Programs/Programs.htm
>
> It says 420 ohms and I measure 460 at 105kHz.  About
> 50 watts to the
> IGBTs and about 50 watts burning in the secondary!!
> Fortunately, the
> secondary is big with lots of high emissivity
> surface area...  Those
> losses might be less significant with "better"
> streamer modeling...
>
> The new version of ScanTesla will also give IsecRMS
> now...  The AC
> resistance of the secondary is a "new thing" that we
> always knew
> would "get us" one day ;-))  That day is here!!
> Rsec is now a major
> (50% of the loss) coil power loss with the SISG!!!
> I was going to
> wind a new secondary with aluminum wire...  I may
> have to rethink that...
>
> 700 amps is a lot and it take the very best "little"
> (TO-247 style)
> IGBTs to handle that without getting real hot.
> Isotops and bricks
> don't care though.  The big worry is heat on the
> IGBTs....  Hard to
> say how hot a random IGBT will get...  I get the
> feeling that a
> current spike alone will not kill them, but "heat"
> will...
>
> The data out there is of no use for running IGBTs at
> say 20X there
> ratings :o))  Thus, I have no answer for Brian
> Foley's IGBT question either...
>
<snip>
>
> Cheers,
>
>          Terry
>