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coax withstanding voltage

Discussion in 'Electronic Design' started by kell, Nov 29, 2004.

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  1. kell

    kell Guest

    Is there such a thing as coaxial cable with a high enough dielectric
    withstanding voltage to use as spark plug wire? i.e. >>50kv
    Did a little googling but didn't see much.
  2. Ian Stirling

    Ian Stirling Guest

    I recall typical 'working' voltages of 2KV in many cables.
    I suspect many low-loss solid polythene dielectric cables would probably
    qualify, though may not be specced for it.
  3. Jim Thompson

    Jim Thompson Guest

    IIRC, teflon insulated RG-8 coax will do 30KV, at least.

    ...Jim Thompson
  4. Carl Ijames

    Carl Ijames Guest

    Is there such a thing as coaxial cable with a high enough dielectric
    A company called Nology sells grounding sleeves to go over spark plug
    wires. Be aware that this creates a capacitor that gets charged up by
    the discharging coil to whatever voltage the plug fires at, which then
    discharges with a much shorter time constant giving much higher peak
    currents (same capacitive transfer circuit used in lots of pulsed
    lasers). Nology claims wonderful amounts of peak power from this
    scheme, 10-100x what the coil discharge would normally give. What they
    don't tell you is that if the mixture isn't sufficiently uniform in the
    chamber you can get lean spots and if one of them is at the plug it
    won't light off during the now sub-microsecond discharge where the
    millisecond coil discharge would have allowed time for the mixture to
    change and light anyway. More important, this gives huge kA current
    pulses which can wreak havoc with computer sensors (can you say rfi and
    ground bounce? :)). Also, the dielectric of normal spark plug wires
    isn't designed to handle this stress and doesn't last. I'm sure Nology
    is on the web.
  5. Marc H.Popek

    Marc H.Popek Guest

    1.5 inch coax is used at 50 KV working voltages... thick unruly cables!

  6. Look at aviation ignition leads.
    Most of these have a shielded 'braid'.
    Remember though, you also have to work out how to do the ends very
    carefully indeed. The aviation ones have a ceramic insulator in the plug,
    and a external thread on the plug, with a clamp nut assembly that grasps
    the braid, which ends about an inch before the end of the insulator

    Best Wishes
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