Re: Marx Bank Charging Supply

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Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


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From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, April 27, 2002 12:05 PM
Subject: Re: Marx Bank Charging Supply


> Original poster: "Jonathan Peakall by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jpeakall-at-madlabs.info>
>
> Richard,
>
> .but if you are basically after big, loud sparks rather than precise
> > waveforms, inductors are much more hassle - the inductance has to be
> > pretty high to avoid the DC path becoming significant and sapping the
> > energy after the initial firing, and also think about the standoff
> > voltage the windings would have to sustain. Resisters will be much
> > easier.
>
> How much loss are we talking here? With a small 15kV or so Marx, I didn't
> *see* much difference between resistors and inductors. I don't have
> equipment to measure big DC pulses, so this is just judging sparks by
size.
> Many of the designs I see out there use inductors. I haven't found any
cheap
> source of HV resistors, and if I build a unit using lesser rated
resistors,
> I would be worried about breakdown/repair. This happened on a smaller unit
> of mine.

The typical Marx only needs a few tens of K for the resistors... water
resistors made from cheap vinyl tubing and copper pipe caps will work quite
nicely at high powers...  Get some copper sulfate and have at it...  Other
alternatives would be fairly fine nichrome wire, or long wirewound
resistors...Carbon/graphite pencil leads (or carbon arc rods) would also
work.. It's not like you need 0.001% precision for this application..

Resistor sparkplug wire is another good source... You should be able to get
old sparkplug wires for free (ask at places that do tune-ups and
autorepair)..

If you can find a cheap source for standard wirewound resistors that are
3"-4" long that will work just fine... figure around an inch for every 10 kV
plus an extra inch.  Sure, you might blow a resistor up due to a failure,
but that's part of the fun.