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180kV Marx Generator

180kV Marx Generator

Marx generators are quick, simple, and easy to construct voltage multipliers consisting of only passive components; capacitors, resistors and spark-gaps. Because of their design they are only suitable to provide high current, high voltage pulses which last only fractions of a second.

Schematic

A Marx generator works by charging the capacitors in parallel via resistors, and discharging them in series. Once the capacitors have charged enough the first gap will breakdown, and the voltage across the two capacitors will have doubled. Since the resistance of the ionized air in the spark is much lower than the resistance of the resistors the capacitors are effectively in series. The next gap will breakdown immediately due to the increased voltage across it's gap and this chain reaction continues up the ladder. The voltage across the chain of capacitors will be the sum of all their voltages, and enough to spark to either ground or another Marx generator if in a bipolar setup.

Cheap high voltage capacitors can be found easily on ebay, for my generator I purchased 20 ceramic caps from China. Proper HV resistors are much harder to find, especially in large quantities. Fortunately they can be constructed by putting several regular 1W resistors in series.  I used 3x 330k 1W carbon film resistors which were soldered together and then sealed with heat-shrink tubing as shown in the photo. When constructing the actual circuit the components should be soldered together free-form to aid voltage stand-off. The resistors were soldered together in long chains, with capacitors joining each chain and simultaneously forming the spark gap. Once completed I found it necessary to encase the capacitor's legs in additional epoxy to prevent arc-overs.

HV resistor construction of Marx gen

For the high voltage source I used a flyback transformer  which was run from the "555 driver basic", which could provide about 20kV. The voltage provided by the source isn't too important as it is limited by the first spark gap. The whole setup was then glued onto an ikea cutting board for easy use. Although a theoretical maximum of 300kV is possible (20 stages * 15kV across each capacitor) I'm not too keen on pushing the capacitors right to the limit, especially since arc-overs started when the spark gap was still set much below 10kV. There's no room for larger sparks anyway. :-P The spark in the photo is 18cm long, which is the maximum achievable with the spark gaps set to where they are. I would assume the spark's voltage to be slightly under 180kV. Photos taken later with my new digital camera have revealed that the repetition rate is actually close to 14Hz (upto 7 sparks in a 0.5 second exposure), not too shabby for something using the cheapest parts available!

completed Marx generator Marx generator spark 0.5s exposure of spark gap




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This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.

Disclaimer: I do not take responsibility for any injury, death, hurt ego, or other forms of personal damage which may result from recreating these experiments. Projects are merely presented as a source of inspiration, and should only be conducted by responsible individuals, or under the supervision of responsible individuals. It is your own life, so proceed at your own risk! All projects are for noncommercial use only.