Re: DC power

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

Original poster: "Chris Swinson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <exxos-at-cps-games.co.uk>

Hi Larry,
> I've been experimenting with a charging system
> much like yours. One thing to think about is that
> all the charging has to take place while the arc
> is still lit, which means for normal gap speeds
> there is only a few hundred microseconds to get
> your cap charged. A good reason to stay away
> from big charging inductors, at least for this application.

Yes I did think about this and I thought there was only one way to find out
so I built it. If I run the gaps at very low speed, something like 1 bang a
second, the main sparks do jump a bit further but not really that much.


>
> I am using a 42 mH air core inductor wound with
> #22 wire, 12.5 inches in diameter and 12 inches long.
> It limits charge current to 40 amps at 20kV. A diodes
> peak repetitive pulse current is about 1/4 to 1/5 of the
> non-repetitive peak usually listed in the spec sheet,
> so the charging diode should be somewhat robust. I'm
> using an 8 Amp RMS, 400 A. peak,  48 kV diode with
> no failure yet.

> Works quite well, too - the cap is charged to almost
> 2 X the supply voltage. At the moment I'm fighting
> with flashovers at the gap at higher power.

The inductor is giving the voltage a boost ? unless I've missed the point.
with my NST secondary that was large and the voltage might have been boosted
a lot though it did run for a few seconds before the diodes blew and there
was no real extra power there either. Which makes me think the tank cap  is
the same voltage no matter what you do. I think I will try more tank
capacitance just to see what happens then.  I might also try a larger
secondary to see how that changes the spark length....

Chris