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Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
A few months ago I bought one of those Chinese Marx generator kits that you see on E-Bay. Mine is the largest 20-stage model. It is surprisingly well made, better than I expected. The HV power supply is a flyback transformer driven by a ZVS driver, both supplied with the kit. I initially used a laptop power supply for the ZVS driver input. After about 30 shots, the laptop power supply died. I had also noticed that there was arcing between the input pins on the flyback transformer every time it fired even after I potted them. I then changed over to a 24-volt battery power supply for the ZVS driver consisting of two 12-volt AGM batteries in series. I did this to completely isolate the Marx generator from the house power to prevent any damage to anything I might have plugged into the house power.
Upon further operation I again noticed that there was arcing between the flyback transformer pins. This bothered me a lot. After about 20 more shots, the ZVS driver died. The HV kickback apparently destroyed the drive transistors. I then replaced the ZVS driver with a new one. This time I turned off the lights to see if I could see anything. Sure enough, I saw arcing between the leads of each of the two 10M ohm charging resistors connected to the flyback output. These resistors are 40 mm in length and are rated for 15 KV which apparently is not enough.
I then ordered two 10M ohm HV resistors which are 100 mm in length. The voltage rating was not stated but I estimate it at about 35 KV based on their length. Upon replacing the two 40 mm resistors with these 100 mm resistors, the problem was solved. There is now no more arcing between the flyback input pins nor between the flyback output resistor leads. I can now operate this Marx generator without worrying about destroying the ZVS driver or the flyback transformer.
The moral of this story is that, as is typical of many Chinese products, you frequently have to modify them in order to make them work properly.
It is true that chinese products can´t compare to good american or soviete stuff, but unless your application is critical or you need durability, you can´t beat the chinese price. I mean, a 15kv chinese cap may be good for only 5kv, but you can use 3 in series and still be at half the price of the soviet cap.
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Modification to Chinese Marx generator
