Re: Small DRSSTCs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

I have constructed a very small DRSSTC:

http://www.stevehv.4hv.org/DRSSTC.5.htm

The secondary is only 7" tall... i cant see why you would go smaller
than that.  Performance is outstanding for its size as it pumps out
18" streamers.  Its an older design, so if i were to build it again it
would be a bit different.  So far it hasnt blown a single IGBT, the
only failures have been 1) inadequate MMC, and 2) poor solder joint on
my primary connection, went open circuit at a thon and i didnt realize
it until later.

If you do wish to get into DRSSTCs you will have to learn to accept
some failures, as most people encounter at least a few when they first
start out.  Once you get the hang of things, it goes much better.  My
first DRSSTC (the first to actually use feedback ;-)) smoked lots of
IGBTs as i learned what needed to be changed to make them work right.
Now that i have a much deeper understanding of these things, i often
have zero failures with new designs.

Now onto your other questions:

On 12/4/05, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>
>
> 1) The list has been buzzing with the success of ever-larger and more
> impressive DRSSTCs, with even larger ones on the drawing board.  But what
> about the other end of the spectrum?  Some of us may wish to build much
> smaller versions for tabletop fun and portability.  But as size goes down,
> the secondary resonant frequency goes up, and can be in the 200-500 kHz
> range.

Use very fine wire and dont worry about the Q so much...  it works just fine.

>
> Question - are IGBTs available that can work well at much higher Fs?

Some are rated to 200khz or better with resonant switching.

> Current capacity & voltage rating need only be enough to produce leaders
> measured in inches for tiny coils, to about 3 feet for larger desktop
> models.  Any suggested manufacturers & products?  Any general design advise
> for building small DRSSTCs?

See my website:

http://www.stevehv.4hv.org/

>
> 2) Suppose one wanted to buiild a twin coil DRSSTC.  Does anyone see a
> problem in using feedback from just one of the primaries or secondaries?

Use primary feedback, much more stable as i have proven over and over
again.  And yes, it should work just fine assuming your secondaries
are well matched... same issues as a SGTC twin setup.

  I
> think all would be well for leaders jumping between the coils, but what if
> one coil experiences a ground strike and the other one doesn't, etc?

This same problem exists with spark gap coils.  Usually its ok so long
as the center point was grounded between secondaries.  If not, it will
put a HV node at the 0V connection between coils, could be a problem.
Best not to let them arc to ground, and only to eachother.

Steve Ward

> Experts, any thoughts?

>
> --Steve Y.
>
>
>