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can anyone tell me what a spark gap capacitor is?

Discussion in 'Electronic Basics' started by [email protected], May 3, 2005.

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  1. Guest

    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?
     
  2. Don Bruder

    Don Bruder Guest

    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... <shrug> 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.
     
  3. SioL

    SioL Guest

    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.
     
  4. colin

    colin Guest

    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 =^.^=
     
  5. John Larkin

    John Larkin Guest


    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
     
  6. Jamie

    Jamie Guest

    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.
     
  7. Guest

    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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