Re: SSTC

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Herwig,

At 11:31 AM 12/18/2002 +0100, you wrote:

>Hi SSTC coilers,
>
>Spark gaps are said to cause up to 1/3 of a TC system's losses. In
>order to reduce these and as NSTs are rare in this part of the world,
>I'm planning on substituting the static spark gap of my small 2"
>system with silicon. Of course the system needs to be redesigned.
>
>1. Does John's formula "input power vs streamer length" still hold or
>could I expect a distinct improvement?

Assuming the SSgap is very good, you could almost expect 50% more power to 
the streamers so maybe the equation would be:

L = 1.7 x SQRT (input power x 1.5)

Hard to say for sure since it depends on a number of things, but it should 
certainly do much better than a conventional gap.


>2. Are there any drawbacks (besides of $$ of course)?

It is tricky trying not to blow up the silicon.  A nice scope and 
current/HVvoltage probes really help.  One maybe big problem is that a 
small coil will run at pretty high frequency so the losses may be higher 
than say my 36.5kHz OLTC.

John Freau mentioned "So far there has been no efficiency improvement if I 
remember correctly. "

The gap itself is very efficient.  It can switch 3 joules at 120BPS (2500 
amps!) while barley getting warm.  My problem was much more silly 
convention secondary low Q losses since I have so much small wire on a 
lossy cardboard form.  The gap part works great!!  I also loose some power 
having to switch like 2500 amps, but my stupid secondary is most of the 
problem.  Should have been plastic...  However, as time goes on and it gets 
drier and drier, the Q is constantly getting significantly better ;-))

I still have not manage to run it at really full power (240VAC 
in)...  Hopefully, some other projects will get finished up soon and I can 
get back to it ;-))


>3. Searching the archives I've found that half wave rectification is
>used often. Wouldn't full wave rectification result in a higher
>throughput? Could one of the experts please enlighten me?

Half wave seem to work very well if the input is DC.  AC switching may not 
really work better since a fixed diode for the reverse direction is pretty 
efficient and simple.


>Cheers
>
>Herwig
>---------------------------------------
>Greed is the root of all evil!
>---------------------------------------