i went to an electronics store today looking for high voltage capacitors for building a marx generator,the lady behind the counter was as confused as i am by the name spark gap capacitor. can anyone tell me how these are any different if at all from regular capacitors, and would they work for a marx generator?
No difference in function, but maybe a difference in construction - A cap specifically intended for spark-gap use might be built a bit "beefier" to avoid frying it with the high voltages that a spark gap wants to run at, or with different materials so that its "dump" speed is faster, but aside from that... A cap is a cap is a cap, at least as far as basic function is concerned.
Basically, it sounds like you're looking for a high voltage rating, high capacitance unit. What voltage range are you expecting the spark gap to fire at? Use that as a base, and look for something rated for at least that high a voltage, if not higher, in the mFd/pFd range your tuning calls for. Your main worry is probably going to be arcing between the plates and the possible resulting "pop" (or maybe "KABOOM!", depending on how much power you're running) that can result from exceeding the breakdown voltage of the cap's dielectric material.
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It's usually a ceramic disc cap that has a slit sawed a bit of the way down from the top edge of the disk. Imagine cutting a small rectangular slice out of a pie. When the voltage gets high enough, an arc jumps between the exposed metalization layers, protecting some other circuit component, or the cap itself, from overvoltage.
John
yes thats what this is, its a capacitor with a built in spark gap in parallel, it often looks like a totaly ordinary ceramic capacitor with a slot machined into the top of it.
theyr often used for protecting high voltage electronics where even higher voltages are used such as in CRT where the high voltage EHT might arc over to other electrodes ocasionaly. youl find them on the base of most CRTs
not sure they have any use for a marx generator though.
Colin =^.^=
Maybe the answer is hidding in this last sentence, it might be a cap with two safety electrodes (air gap) that discharge when voltage comes close to maximum allowed voltage for that cap thus protecting the cap from explosion/destruction.
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just two plates close together that will arc.. also they made ceramic caps at one time that has a spark gap cut in them but i don't think that is what you want. check a guess.
thanks for all of your help. i plan on running this generator at the low end of high voltage, the caps they had were rated at 2 kv. as for the capacity, 1nf. i am not planning on blinding 2 foot arcs here, just a little high voltage generator to "play" with. while wre on the subject of capacitors, when using dc pulses and a capacitor to even them out do capacitors maintain voltage while amperage drops between pulses or the other way around? thank you so much.
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