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teravolt

Mon Feb 22 2010, 03:59AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I would use carbon comp but I don't have a economic source at the moment. another option is to use liquid resistors or inductors. Does anybody have a good formula for charge time? here is some progress I've made. The two halves that you see in the picture will be stacked for a 10 ft marx. One problem is that I am not shure how much of a crack it will make and I may have to find a place other than my back yard to test it. Cheers.

wylie

Tue Feb 23 2010, 05:47PM

Registered Member #882 Joined: Sat Jul 07 2007, 04:32AM
Location:
Posts: 103

One problem is that I am not shure how much of a crack it will make and I may have to find a place other than my back yard to test it.

How about enclosing the discharge in a long plastic tube, like people do with sparkgaps? Or would the tube diameter have to be WAY too large at those voltages to prevent the discharge from just running down the plastic?

Proud Mary

Tue Feb 23 2010, 07:01PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Professionally designed Marx generators often, but not always, use resistance wire resistors, sometimes wound from the centre in opposing directions by way of a self-cancelling inductance.

teravolt

Tue Feb 23 2010, 08:33PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

maby some technit would work

mikeselectricstuff

Thu Feb 25 2010, 12:46AM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
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Posts: 253

teravolt wrote ...

One problem is that I am not shure how much of a crack it will make and I may have to find a place other than my back yard to test it. Cheers

Based on my 2.2nf/stage marx, 32nf at a decent voltage will be seriously LOUD - neighbours will definitely notice! Significant risk of being mistaken for a gunshot....

My marx did once result in a visit from Police, but that was becuase I forgot to ground the garage door, it glitched my alarm which sent a panic signal...

teravolt

Thu Feb 25 2010, 03:59AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I have found some 1M ohm metal film resitors that have a 10kv rateing

and I figured that liquid resitors are almost as costly and a lot to setup so I will probly buy 500+ if the options don't change like maby inductors. If anybody wants to pigyback my order let me know soon at .26cents ea, 1W 1MEG 10kv pulsed.

I was thinking, the shorter one can be erected first to see what happens. it is about 20 stages.

klugesmith

Thu Feb 25 2010, 06:56AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

teravolt wrote ...
I have found some 1M ohm metal film resitors that have a 10kv rateing
...I was thinking, the shorter one can be erected first to see what happens. it is about 20 stages.

Are you planning to trigger the discharge, or wait for one spark gap to fire spontaneously?

At your level of capacitance and with multi-megohms of resistance per stage, the time constant of the charging ladder becomes substantial. It's proportional to R, C, and the square of the number of stages.
With 20 stages (not to mention 40 or 50 stages), voltage on the last capacitor could lag that on the first by a minute or more. If you charge too rapidly, the early-stage spark gaps could fire before the late-stage capacitors have anywhere close to their full energy.

Depending on your charging supply and number of series resistors per stage, you might want to order a value much smaller than 1 megohm, for speed. At the risk of overheating the early-stage resistors as you charge the bank.

Proud Mary

Thu Feb 25 2010, 04:28PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The design, engineering, and insulation of a compact 1.5MV Marx generator is described in detail in the link below. It is rather less ambitious than yours voltage-wise, but still has much to commend it:

hboy007

Thu Feb 25 2010, 05:08PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374

as to the resistors, has anyone tried rods of annealed clay-carbon mixture?

teravolt

Fri Feb 26 2010, 05:08AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I have been only able to find the quantity that I need that is afordable at alied. when the two peaces are put together there will be 51 caps 10kv X 5 X 110 and I can get a good price break at 500+.
One other problem I am having is weight I may have to section the big one because I can bearly lift it. the spark gaps get put this weekend and I haven't approched how it will be triggered. I ceranly don't want it to erect in the middle. Probibly a uv illuminator will have to be devised at the bottom gap. When I set up the door knob marx it self broak about 30 seconds the caps are 1700pf and the resistors are 1.5M X 20 stages with 2.5 ft sparks. On the side I am doing a spice simulation but I don't think I will be able to get 50 caps in it but I can get an idia of a smaller section charge time. Keep the idias comming N.B.

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