Re: Marx using inductors (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Mon, 26 Jun 2006 09:16:14 +1200
From: m.j.watts@xxxxxxxxxxxx
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Marx using inductors (fwd)

Hi Jonathon,
                     I built two Marx banks using inductors in the past 
(see comments below):

On 22 Jun 2006, at 7:42, High Voltage list wrote:

> Original poster: Steven Roys <sroys@xxxxxxxxxx>
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Wed, 21 Jun 2006 13:14:48 -0700
> From: Jonathan Peakall <jpeakall@xxxxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: Marx using inductors (fwd)
> 
> Thanks for all the replies.
> 
> While digging around I came across some HV (I think) resistors. I am not
> sure if they are wirewound. They are marked :
> 
> CVD 1%
> RN30X
> 5004F
> 5M
> 
> Thet are about 52mm/2" long and they do indeed measure 5mOhm as the 5M
> suggests. I have 20 of them. Would it matter if they are wire wound or not?
> 
> As for the rest of the system, I was thinking of using a 12/120 NST that I
> have, running it into a voltage doubler. If I did the mat right (always
> doubtful) I should wind up with about 33.6 kV. That leaves me a little more
> margin for the caps than I'd like, but a 15/120 NST would be 42kV, too high
> for the caps.

Just set the gaps to suit the caps a la TCs.
 
> If I did use the resistors rather than inductors, how would I calculate the
> break rate, assuming the 12/120 NST, a voltage doubler and the 5mOhm
> resistors? I realize factors like corona loss, etc, will come into play, but
> just looking for a way to ballpark it.

The breakrate with resistors would be in the dirt. Calculate using 
RC time constants. For a first approximation forget about coronas. 
A properly designed system shouldn't have them anyway. The 
whole point of going to inductors was to allow high(er) firing rates 
plus minimizing power loss in the charging process.
  
> As to the inductors, I had thought about ferrite cores, but for some reason
> figgered that that wouldn't be OK. Of course, unless I can scrounge the
> ferrite slugs they will add cost too. Any figures on what the minimum usable
> inductance is?

Ferrites work well. I used ferrite rods designed for use as radio 
aerial rods. Saturation shouldn't be an issue for two reasons:  
inductor current is limited by the erection/discharge time of the 
bank and the end-end airgaps are huge. 

       As to inductances, I got the idea for my Marx's (before I heard 
that it was commonly being done) from reading the Amateur 
Scientist article on the pulsed UV laser using a Blumlein switch. I 
never built the laser but did build the switch and was impressed by 
how little inductance was required to do the job. The more the 
merrier of course and my Marx's used several mH per choke but 
the original Blumlein switch had an inductor of just a few uH.
 
> Thanks for all the suggestions. I will indees use Tesla coils style
> construction, sand and finish the PVC and make  2-3 stages first and work
> out the kinks.

A word of warning - the thing is an electronics killer par excellence. 
Right this day I am repairing a piece of equipment which had been 
mothballed at the time I was conducting Marx experiments in the 
workshop and was dug out for revival a few days ago. The tally so 
far - 10 logic ICs. I spent three days repairing workshop carnage at 
the time. Ignorance was bliss until I realized too late what I had 
done.

Malcolm