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Re: Question about DC resonant charging
Tesla List <tesla@pupman.com> on 14.04.2000 05:08:49
To: tesla@pupman.com
cc: (bcc: Marco Denicolai/MARTIS)
Subject: Question about DC resonant charging
>Original Poster: "David Dean" <deano@corridor.net>
>
>Questions to you who use DC resonant charging.
>
>Do you use a choke that is resonant with the tank cap at some
>breakrate?
<SNIP>
>I think now after thinking more about it, that I do not
>understand what it means, this "DC resonant charging".
<SNIP>
>I try to use an inductance with a long enough time
>constant with the tank cap to keep it from reaching firing voltage too
>soon. But the numbers come out with an inductor that is just too darn
>big.
>
>Any insight would be most appreciated.
>thanks,
>deano
Hi.
I went throught your same process one year ago. I have also written a Word
document full of mathematics about it (I can email it to you if you are
interested).
At a glance, it goes like this:
- you have a DC tank: the spark gap will short circuit it
- you need to limit the current -> you need a series inductor
- the series inductor will store energy when the SG closes and give it back
when
it opens: this is the inductive kickback (somebody confuses/calls it resonant
charging)
- the inductive kickback will overcharge your primary capacitor to at least
twice the nominal DC tank output voltage
- if you want to limit it to that value, you have do add also a series diode
from the inductor/SG node to the capacitor
You end up with a series inductor (HV, in the range of 1-2 Henry) and a HV
diode
which are both difficult to manufacture or extremely expensive to buy. The
inductor is also going to be physically big.
That's why I abandoned the whole idea and turned to a switching power
supply. It
took me one year to design a suitable one, but now it's working fine. I get 20
kV DC at 10 kW for some 20-30 kg of weight and a volume of half a cubic meter.
No big pigs, control panels or motorized variacs, just a standard 9U 19" rack.
Regards