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Hi, I am looking to build a marx generator that will fire multiple times a second. I have read some of the threads on marx generators but I have been unable to find anything that discusses how to increase the frequency of the pulses.
It seems with marx generators in general the capacitors have to finish charging before a pulse is fired. Is the answer then to use capacitors with less farads so they charge quicker and then fire quicker?
I was hoping to get the marx generator to have a firing frequency of 50-100hz. Is that even feasible? Are higher firing frequencies than that feasible, like 1khz?
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Basically there's two ways to increase the repetition rate: either increase the current supplied by the charging circuit, or use smaller capacitors like you said. Obviously, using smaller caps will result in less energy per spark, whereas using larger caps and a more powerful charging supply will result in more energetic sparks.
I think you could get a marx generator to fire at about 50Hz if the spark gaps are perfectly tuned to avoid misfires or premature firing. However the electrodes would wear very fast, so it would probably require constant fiddling with the spark gaps. Perhaps you could use tungsten rods for heavy duty spark gaps, similar to the static gaps constructed for Tesla coils.
One solution is to use inductivities instead of resistors for charging the caps. You can make them with a much lower DC resistance than the normal charging resistors used in Marx' (which are normally in the range of 100k or so...). For example I charge my Marx with an inductivity of 400 mH which has a DC resistance of about 1 kOhm. So you can charge much faster. When the Marx fires then the inductivities gets a very high reactance because of the high frequency nature of a fast rising impulse.
Thanks for all the replies, seems like I will definitely be using inductors instead of resistors. I wonder why most texts still refer to resistors first over inductors.
"Gatling Marx Generator" made me laugh. 200 pulses a second with their next version aimed at 1000 pulses a second, those are beasts.
I have a few more questions.
Can AC flyback transformers be put in parallel like DC flyback transformers. I want to increase the power to ensure quick charging speeds and make up for corona losses.
I was thinking of creating a voltage doubler with two 30kV 200watt AC flybacks plugged into one line of a symmetrical voltage multplier and then two 30kV 200watt flybacks plugged into the other AC in. This would give me 60kV DC out at 800 watts which would then feed the marx generator and be 60 kV a stage.
With a goal of around 650kV I would need about 11 stages plus stages for corona loss and other factors.
One last thing are you guys aware of any calculators or formulas to predict the time it would take to charge the marx generator given a certain power supply, inductor resistance and capacitor voltage and farad levels?
Registered Member #2566
Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147
Robert Francis wrote ...
Hi, I am looking to build a marx generator that will fire multiple times a second. I have read some of the threads on marx generators but I have been unable to find anything that discusses how to increase the frequency of the pulses.
It seems with marx generators in general the capacitors have to finish charging before a pulse is fired. Is the answer then to use capacitors with less farads so they charge quicker and then fire quicker?
I was hoping to get the marx generator to have a firing frequency of 50-100hz. Is that even feasible? Are higher firing frequencies than that feasible, like 1khz?
Thanks
with high repetition rate (> 50 pps), and input power over few hundred watts, you will have problem of cooling spark gaps. i would expect marx generator firing very erratically without taking care of that.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Robert Francis wrote ...
Can AC flyback transformers be put in parallel like DC flyback transformers. I want to increase the power to ensure quick charging speeds and make up for corona losses.
With a goal of around 650kV I would need about 11 stages plus stages for corona loss and other factors.
I can't see any reason why you can't parallel 'any' type of transformer, as long as they are driven in sync.
The highest voltages I've seen produced by 'amateur' multipliers or Marx's is around 200kV. While I've been working on a project for some time to achieve ~630kV, the only way we think this 'might' be achievable is to put the multiplier under 'high vacuum', which involves some 'very expensive' military grade diodes, not to mention some form of 'vacuum capacitors' in order to prevent outgassing problems. I've been working on this on and off for around five years now, and I still have problems to solve (and diodes to buy) before I can start construction.
EDIT: Tesla coils can easily achieve these voltages, but not in the kind of 'controllable manner' that I suspsct you want to achieve.
Registered Member #1521
Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128
I made one several years ago, with 500uH inductors. Never calculated the output repetition, probably it's around 10-15Hz. I think it's possible to make a 1kHz one, but it needs proper calculations, and building. Video
@ Ash, his estimates may have been wrong but this guy estimated he had about a 1 million volt marx generator and he was just an amateur.
He used 2 generators, one positive one negative. When he tried to link the 2 generators together as just one he got considerably less spark length though due to corona losses.
@ omegalabs Thanks for the video, I'll have to find out the best uH inductor levels for fast enough charging while still providing protection to the capacitors. What was the power supply wattage on your marx generator?
@ dex, some of the commercial units I have seen submersed the generator in oil or used compressed air between the spark gaps but I want to avoid that if possible. I am not sure what I will do about heat.
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High Firing Frequency Marx Generator
