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Registered Member #2732
Joined: Thu Mar 11 2010, 07:48PM
Location:
Posts: 4
Hey all,
We are a team of students making a Marx generator as part of a project. We are using 4 kV caps and 1 Mohm resistors and our classic generator currently has 8 stages. We are currently experiencing a few problems with the distance needed to generate sparks and the voltage along the generator. The only way we can have a spark, usually only the first spark gap, is if the two ends are extremely close ( the sparks are barely visible). The other thing we noticed is that there is a significant drop in voltage along the generator (50% or more). The input voltage is currently only 500V, but from what we understand we should still be able to make the generator function. Surely when we move on to a higher input voltage sparks would come more easily, but wold like to make sure our circuit is configured for optimal performance and not just compensate for losses with more voltage. The only thing we could think of that could explain the problems we are having is that perhaps the resistors are not the right value for our needs.
Any tips you could give us would be greatly appreciated.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
For smooth large-radius spark gap electrodes (not 'pointy') allow 3kV per mm. At 500 V you will need a very small gap. When the spark gap 'fires' allow about 300 V drop. In a Marx generator with tens of kV per stage it's not a problem, with 500 V per stage you're lucky to get any final output. Go straight to 4 kV to see better performance.
I believe that the uv from one 'firing' gap will help to 'fire' the next, so try to put your spark gaps in line to benefit from this effect.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
the trick to a marx generator, in my experience, is twofold: one, tune your first gap, two: have enough voltage between the first two stages such that the voltage of the two capacitors now in series from the first gap firing will easily exceed the voltage necessary to fire the second gap as 500V you are really lucky to get anything at all, as even with the first gap closed that only leaves 1kV for the second gap, so it too will have to be very small
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
A guy once showed me a "trick" that piggy-backs on this discussion. He would use a long delicate needle nose pliers to first curl the ends of the leads prior to soldering and the consistency of the curl allowed a very close, consistent gap.
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Marx generator project problem
