Wednesday, 14 September 2011

Marx generator.

Marx generator is a voltage multiplier that multiply the high voltage direct current to a higher voltage level, by charging a group of capacitors in parallel, and discharging them in series.

I built a Marx generator with original intention to increase input power into my Tesla coil, but didnt working. However its still working as a Marx generator itself, so still worth mentioning in this blog. :P

The operation of Marx generator can be best understood by studying the diagram, retrieved from Wikipedia:

My version of Marx generator has no major difference from any other versions. i used three-stage multiplying, using three 2-litre bottle saltwater capacitors wrapped in aluminium foil as plates. Each of the capacitors was measured to be 5nF in capacitance. There are three spark gaps, where two are small spark gaps as switches and a final spark gap. I ve made the final spark gap larger than the other two, and connecting it directly to ground instead to a voltage divider and load ( as depicted in the above diagram).

For the spark gaps, I have two small spark gaps each of 1.5mm gap length ( it varies around that value cuz u need to synchronise it to get best length in order to avoid corona discharge, cuz corona discharge between the gap may spoil the operation). The spark gap was made by screwing two metal screw into a circular former, either by using glue tape roller, or plastic bottle caps. I used screw to enable easy synchronisation of the gap length during operation.

All the resistors are at 1 megOhm each. The final(big) spark gap was also constructed similar to other two spark gaps. Initially i set the final spark gap length to be 0.5cm, and increased it gradually to get the maximum spark length that can be obtained from the overall configuration of the Marx generator. The maximum spark length observed is about 1.5cm. Yes, its too short for most hobbyists, due to small number of stages ive been using. I am intending on buying more high voltage capacitors to reduce size ( saltwater capacitors are too big and heavy) and make the overall design compact and smaller ( and portable as well) as well as increasing the number of stages to maybe 20 to 30 stages. I wonder how long the spark i will get...

Here is the schematic of the marx generator built:

Here are the photos taken:

The overall setup. Ignore everything outside the A4 papers boundary. Just focus the interior. The noticeable three big bottles are my saltwater capacitors of 5nF capacitance each. I m using my ZVS power oscillator (but changed the 1N4007 diode to BYV26E, IRF840 transistor to IRFP250N, and 10nF capacitor to high voltage rating 1uF capacitor for faster switching, cooler mosfet and higher efficiency and power) fed the oscillating power into the flyback transformer. The transformer rectified the oscillating current in it so there is no need to use diode. The high voltage direct current is then fed into my Marx generator.

Closer view.

Power supply ( laptop power supply, 12V,3.16A as always used before) which is the black wire with yellow wire at its end, breadboard populated with components in ZVS oscillator confg, and a flyback transformer ( the only chunky thing close to the breadboard)

Capacitors and small spark gaps bird eye's view.

Closer look on the small spark gaps. The white one was not used, so i closed the gap.

The small spark gap using screws and plastic bottle cap.

Another small spark gap, also using screws and plastic bottle cap.

As mentioned before, this small spark gap is not used, so i closed the gap. This was constructed cuz i though another small spark gap would be necessary before the final big spark gap, but when finding out it wasnt important later on I just leave it there by closing it. This gap was constructed with glue tape former and two screws.

This is the final and the biggest spark gap where the final product of the Marx generator ( the longest spark) will be observed. It was constructed similar to the unused small spark gap. Just ignore the red tape former over it cuz it is just to hold the wires carrying voltage to the final spark gap in place.

Final (big) spark gap.

Here is the video. I have to put on a video this time cuz it was really hard to capture a photo of a flashing spark. Enjoy it!

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