I need some long resistors to make a marx generator. The value can be anything from 1k to 100k, but they must be long enough to put up with 200kv for a few microseconds. Any good ideas?

 

Its not the length that imprortant but its Watts,

P = V*V / R

P = 2000 * 2000 / 100000 = 40W

So you should find a resistor of 100Kohm and 40W.

 

I disagree, the length has to be enuf that the resistor will not arc over at 200KV. I have four 2 meg resistors that are 1.75 inches (4 cm) long each. You can have them if you want them.

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hawly cow! 200kV ! :shock:

What kind of material are these types of resistors made of?

 

Most folks only think that resistors have "value" and "wattage" ratings. They don't realize that they also have voltage ratings. A typical 1/4-watt carbon film resistor is rated at 250 volts while a 1/2-watt unit is rated at 300 volts. Intermittently, they'll handle 750 volts. That's why you often find lots of lower-value resistors strung together in series in higher-voltage circuits, such as for voltage dividers. In fact, Tek used half a dozen 1/2-watt 510K ohm resistors in series in the focus section of the CRT circuit for just that reason.

Of course, 270 of them in series for that intermittent rating for the 200KV is a little ridiculous! HV resistors are often made of glass or ceramics. The resistor used as the series divider for the 20KV HV probe for my VTVM was a glass thing about four inches long.

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

to my knowledge the best insulator out there is mica. I t is rated a 2 million volts at a thickness of 1cm (2/5 of inch). for something like this only glass or mica will work. You could try winding your own resitors out of nichrome wire for something like this.

Sounds insane, but where are you gonna get a 200kv rated resistor, ey???

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Are you actually inputting 200kv, or is that the intended output? If it's the output, you don't need each stage to have 200kv resistors, they only need to withstand the charging voltage. Some people also use inductors instead of resistors.

As for buying high voltage resistors, I would start my search at Newark and ebay.

 

I've seen 50kV resistors for sale for a few US dollars (maybe 10).. They will probably withstand 200kV for a few microseconds.