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Marx Gen help

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LowCurrentHV

Tue Feb 28 2006, 11:22PM

Registered Member #272 Joined: Tue Feb 28 2006, 11:07PM
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Posts: 3

I have just recieved 100, 15KV 100picoF capacitors. I also have 60, 1Mohm 1W resistors. I was wondering if anyone had some ideas on how I may be able to get the most bang for my buck. I was thinking about making strings of 5 caps in parallel to bring each string up to 500picoF and placing 5-8 of these stings in the marx generator configuration. I also think I will use two resistors in parallel to provide only 500kohm but able to handle 2W. Charging I don't have an established idea although I might try to play around with a flyback, or NST as 15KV is a common voltage rating on them. I also would appreciate a good method of triggering the reaction without having to put a straw stuck with a needle between the first gap.

And anyone who can answer this question will be greatly appreciated.

After how many stages does it become pointless to charge the capacitors due to loss over the resistors?

Thank you,
Alex

EDY19

Tue Feb 28 2006, 11:58PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
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Posts: 408

Well, if you have 15kV capacitors, you do not want to put 15kV in, since that voltage is the RMS. a transformer rated at 15kV actually has voltage peaks at ~21kV, so I would stick with a 10kV transformer or less for input. Also, I think 500k is a bit too low, as at the beginning of every cycle, the resisotrs will see 450W if you used 15kV. Even though the actual "RMS wattage" is lower, Just having a bit more resistance per stage would help a lot.

LowCurrentHV

Wed Mar 01 2006, 12:31AM

Registered Member #272 Joined: Tue Feb 28 2006, 11:07PM
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Posts: 3

Thanks, hopefully I'll be able to get some photos up of it firing, it will be crude, because I just want to test out the components, and it will probably only be at about 5KV a stage, but I should hopefully get some nice shots. Any more advice would be great.
Alex

Philcogrump

Wed Mar 01 2006, 01:15AM

Registered Member #212 Joined: Sun Feb 19 2006, 05:42PM
Location: Texas
Posts: 20

You also might want to put silicone around the resistors, especially those on the lower stages since these tend to arc over first.

Perhaps a flyback (with some type of driver) would be more compact and the flyback already has DC rectification built-in. If you use the NST, you'd need at least a long string of diodes to achieve the correct voltage rating, i.e. 10 1N4007 diodes in series for 10kV rating.

My small marx generator used a small ~15kV flyback with a 555 oscillator and I used some .001uF 20kV disc caps (8 if I remember correctly) which worked nicely with loud 2-3" sparks (about 120kV or so) with only 15V 1A input and did not require that special triggering (with the straw or whatever).

Many of the really high voltage marx generators other members in this forum have built ran at like 1MV to 1.5MV, which is quite difficult to achieve. One topology involved two separate marx gens at 500kV each and the negative and positive ends made a 1MV potential difference.

Marx generators are quite dangerous and the shock can REALLY hurt if you make a mistake. Perhaps you want to start one on a smaller scale before you try something bigger.

govtcontact

Fri Mar 24 2006, 03:12PM

Registered Member #343 Joined: Fri Mar 24 2006, 02:45PM
Location: Los Alamos NM
Posts: 10

There are several ways to trigger your first stage: 1) A seperate HV source/spark, 2) UV, 3) Laser focused at the center of the sparkgap striking Argon to form plasma, 4) X-Ray ...Take your pick, the simplist is #1.

On the resistors, use atleast 1Meg.

The Maarx I built/worked (1.5 MV, 38 Stages, 3 220 pF caps/stage) on used Method #1 above, but there was to much jiitter in firing timing for what we needed so alt methods are being tested.

teravolt

Sat Mar 25 2006, 04:41AM

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

First make a standard flyback circuit with rectification. You will nead to be able to adjust this. make a HV resistive divider that connects to your digital voltmeter. If you need a hv recifier use 1n4007's (1kv 1A ea.)in series. Add 10meg in series between your power sorce and the marx it may help protect your flyback and doides. If you like long stringy arcs use one per a stage and 1 resistor on each side per stage. If you want more bang and flash parallel them. Scematic on google under marx generators. You can use curled wire for your spark gaps. You will need a shorting stick wich is a insulating and connected to ground. Arange them side by side on a insulating material like G-10, lexan, acrylic ect. and connect the resitors and spark gaps. You can find more pictures and directions at "Iwant sparks & Iwant them now" in google under marx generators. the spacing between each spark gap should be about 3/16". If you go over 11kv (70% of cap max kv) charge voltage you risk destroying caps when the marx fires. good luck and be careful N.B.

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