The Spark Gap is perhaps the only part of this coil which is out of the ordinary. Since the spark gap is one of the parts which needs to be adjusted to make the coil run efficiently, I set about designing a spark gap which was able to be adjusted easily and without having to get anywhere near high voltage (This will mean not having to discharge the caps every time and there will be no dismantling involved.) Adjusting the gap is as simple as changing channels on a TV (Very similar feel to the old TV's with a rotary switch). Basically, it is a length of 150mm PVC pipe with caps on both ends. Inside there are 13 copper pipes arranged as a standard RQ spark gap. On the outside of the pipe aluminium 'U" channels are attached to the back of the bolts which hold the electrodes in. Hopefully these heatsinks will help prevent the bolts from getting too hot too quickly and stop the casing from melting. On the back of the assembly, there are holes drilled in the end-cap around the outside so that air can escape quickly. On the front, a pipe comes in at right angles and joins to 4 separate pipes which go in through the front at 3, 6, 9 and 12 O'Clock allowing air to be forced through to cool/quench the gaps. Now for the unusual part: Through the centre of the assembly, there is a PVC pipe which turns, there is a spring-loaded copper pipe which runs parallel to the pipe and electrodes. The pipe and spring connect to the end-most electrode and by turning the 'selector', it shorts out more or less electrodes. Shown in this picture is the gap without the air pipes fitted yet. The pipe shown at the front is the selector shaft. Note also the heatsinks are clearly visible. Another bonus of this design is that with the gap wound all the way down, the gap will be shorted out allowing it to be 'locked down' giving an extra safety bonus.
18/2/2002: Slight design modification decided on. Where the power connects to the first electrode, I am going to connect the power to a thoriated tungsten tig welding electrode which will stop at the edge of the pipe and be centred to it.
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air supply-----> ----------------- electrodes (Blue)
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The air pressure will all be forced down the pipe and past the electrode to quench the arc. This will give me two gaps in one, A blown gap with PWM control on the fan AND an RQ gap all in series. This will give me 2 lots of adjustment on the gap. The only problem with this is that the gap can't be 'locked down'. All I need is a way of selecting the gap number remotely from the front panel (Now that is a pipe dream and unless I get a brainwave, I won't bother trying to figure it out for a while yet.) |
