From: John Larkin
Subject: Re: Combustion-triggered spark gap?
Date: Tue, 26 Nov 2002 08:51:53 -0800
Organization: Posted via Supernews, http://www.supernews.com
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On 26 Nov 2002 13:51:21 GMT, Mike Poulton
>As I was thinking about electromagnetic can crushers, coin shrinkers,
>and other cool devices based on monstrous capacitors, my mind turned to
>the switch needed to discharge such a contraption. The websites I have
>seen speak of either big metal bars (which weld themselves in place) or
>triggered spark gaps. The triggered spark gap is probably the better of
>the two switching methods. As I was considering how to trigger a gap
>which must reliably hold off 25kV, I thought of using a flame. Picture
>a vented combustion chamber with two metal balls in it, spaced an inch
>or so apart. The balls are the spark gap electrodes. Fill the chamber
>with a flammable mixture of propane and air, and ignite with a spark
>plug. The ionized gas would conduct and cause the gap to break down and
>discharge the device. Has anyone ever heard of this being done?
Most triggered spark gaps use a small third electrode that is driven
with a small flash-type trigger transformer. The trigger electrode can
be near one of the main electrodes, so doesn't require a huge firing
voltage. The trigger spark ionizes the gas and creates a bit of UV,
both of which trigger the main gap. It doesn't take much to push an
about-to-fire gap over the edge.
Big marx generators have multiple gaps that must be fired
simultaneously; they are sometimes triggered by illuminating the gaps
with a high-power laser, which causes photoelectric emission from the
metal electrodes. A photoflash might work.