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1.2 MV Marx Generator

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LAN_403

Dr. ISOTOP

Thu Dec 23 2010, 03:42AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Blarg, time to learn how to use SPICE

Pinky's Brain

Thu Dec 23 2010, 09:59AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Would it make sense to use a magnetic core?

Or would the amount of insulation necessary between the wires and the core turn it into an air core effectively any way?

PS. if you happened to have a decent size tesla coil handy (> 1 m) the diode setup actually makes some sense. Charge it through the tesla secondary :)

ubuntupokemoninc

Sat Dec 25 2010, 06:25PM

Banned on 1/22/2011 for repeated rule violations after multiple warnings.
Registered Member #3299 Joined: Sat Oct 09 2010, 08:11PM
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Posts: 220

I can't wait to see this1

would it look like this?

Dr. ISOTOP

Sat Dec 25 2010, 08:41PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Yeah, but with a couple orders of magnitude less energy per bang

Dr. ISOTOP

Mon Dec 27 2010, 06:51AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

What would be the best way to trigger a Marx like this? I'd use a gas-filled/vacuum relay like Mike Harrison does, but 80KV relays are hard to find

I'm tempted to try N2 laser triggering, since I have an otherwise unused commercial nitrogen laser. Has anyone successfully tried this before?

Proud Mary

Mon Dec 27 2010, 10:40AM

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

The peer reviewed literature on Marx impulse genes reveals the following:

A. Choke coupling is rarely used in 'professional' designs. It is too much hassle, and may introduce LC resonance artefacts into the output pulse.

B. To have the lowest time constant, fastest output pulse rise-time/steepest wave-front and least jitter, resistors used in 'professional' designs are usually orders of magnitude lower than the resistors typically chosen by HV enthusiasts, and are often between 50Î© and 20kÎ©.

A field-distortion trigatron type gap is probably the simplest initiator that will produce good results with careful engineering.

The over-volting sequential gap firing model of a Marx will produce such a raggedy wave-front that you will have to hide the machine away to stop neighbours talking about declining standards. One should aim for wave erection, where all gaps fire simultaneously, or as nearly so as possible in the real world.

see: W. J. Carey and J. R. Mayes MARX GENERATOR DESIGN AND PERFORMANCE Conference Record of the Twenty-Fifth International Power Modulator Symposium and 2002 High-Voltage Workshop.

releng

Fri Jan 07 2011, 07:07PM

Registered Member #3586 Joined: Fri Jan 07 2011, 06:53PM
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I got into this discussion quite late, and am somewhat surprised by the comments on the size of the inductors. Obviously, as pointed out previously, they need to withstand high potentials during the discharge phase. However, unless you plan on pulsing this thing very rapidly, I don't see the need for extremely small values of inductance during the charge cycle. Remember that the resistors in a conventional Marx gen, or your inductors in your design, only connect the capacitors in parallel during charging. During the discharge, current flows through the spark gaps and capacitors to your final load (or arc). During the rapid discharge, you might actually want a larger inductance to isolate the stages. In other words, the inductors shouldn't play into the discharge current's path. Since V = L* di/dt, the voltage across the inductors is a product of the rate of current change (di/dt) and the inductance (L). Making the L too small might increase stage loss during discharge.

Let me know if I'm missing something on this.

omegalabs

Thu Jan 13 2011, 11:56PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

A few weeks ago I uploaded a video about my small marx generator with inductors. The inductors are around 500uH, but they are a little different (3-5%), thats why it doesn't make output spark sometimes.
Solenoid inductors are easy to made, and it's not a problem, if 1-2 windings are crossing each other, so it can be made very quickly. I used 0,3mm wire.

cedric

Fri Jan 14 2011, 01:25PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
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in my mind using inductor for Marx ,is reserve for very high repetition rate,and at 80 kv I don't think they will be easy to make ,in comparison a watter resistor can be build to support this voltage ,be calibrated to about any value and are inexpensive and relatively easy to make ,cooper sulfate work great as electrolyte(dissolve in watter..) I use a transparent plastic tube with some high voltage isolated cable to plug the tube with one or two cm of copper as electrode on each side ,the most difficult is to get ride of the bubbles...

Dr. ISOTOP

Mon Jan 17 2011, 12:52AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Water resistors degrade over time - the last thing I want to do is have to shake my 200lb Marx every month

Besides, I've already purchased 1500' of 22AWG wire for the inductors.
And at some point I do want to do high rep rates. My dream is to run this with a 50KV stage voltage @200pps - 200 130J bangs per second should make for a loud, scary, and dangerous display

. Not gonna happen though - 100KV 1A transformers are impossible to ship :(

omegalabs wrote ...

A few weeks ago I uploaded a video about my small marx generator with inductors. The inductors are around 500uH, but they are a little different (3-5%), thats why it doesn't make output spark sometimes.
Solenoid inductors are easy to made, and it's not a problem, if 1-2 windings are crossing each other, so it can be made very quickly. I used 0,3mm wire.

That is a pretty cool Marx - the first high rep rate one I've seen in action

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