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Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
I bought one of those pre-assembled Chinese Marx generators that you see on E-Bay. The one that I bought is a 20-stage unit with 2 nF, 30 KV capacitors and 1 Mohm resistors. It uses simple looped copper wire for the discharge gaps. The charging device is a flyback transformer. It is built surprisingly well, better than I expected. For the first 30 or 40 shots, it would consistently produce 11 inch loud sparks. Lately I have noticed that it misfires occasionally at 11 inches. It always misfires at spark gap number 12. When this happens, all subsequent spark gaps after number 12 do not fire. The next charging cycle, all the gaps will usually fire again probably because there is charge remaining on those latter stage capacitors which is then augmented during the current charging cycle. I have tried adjusting gap number 12 within reason to no apparent effect. Reducing the discharge distance between the main firing leads to amounts less than 11 inches does make the firing consistent. Is there anything I can do to make it fire more consistently at 11 inches or am I asking too much from it?
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
Strangely atmosphere and charge storage, can affect that but I think the problem is a wire has burnt out and only the high voltage arcing the gap that makes it semi work
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
20 x 30 kV = 600 kV and air breaks down at around 70 kV/inch so arcs of up to 8.6" would be expected from simple theory. Using pointed electrodes allows longer arcs. As above, humidity has a significant effect, atmospheric pressure variations have a small effect. If the spark gap electrodes get hot the firing voltage reduces.
I do not know how significant the effect is but I have read that allowing the uv created at each gap to illuminate its neighbour gives faster more reliable firing of all gaps.
A typical SM member approach would be to tweak everything to its limit for maximum effect then try to repair it, or plan version #2
Arcs and Sparks are never big enough, we always want more. But a working 8" arc generator is better than a broken 11" one.
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Misfiring Marx generator
