On 3/23/13 8:33 AM, Scott Moseley wrote:
Has anyone come up with a good electrically triggered gap yet? Maybe something that uses magnetic quenching? If so, then you could sense the voltage across the cap, and then set a firing voltage.
triggered gaps are easy.. use an auto ignition coil as the trigger pulse generator. I built one using copper pipe end caps with holes drilled in them, and a tungsten welding rod as the trigger electrode.
What I have not come up with is a easily replicatable trigger generator for the primary side of the auto coil. I keep thinking that I could modify a "electronic ignition" of some sort, but I haven't had the time to fool with it. You want something that has good isolation, or your trigger timing electronics will surely die.
A very simple scheme like the "triac light dimmer" does work ok, but doesn't give you a lot of control. At least it generates pulses synchronous to the power line, though. And it's tough, and cheap.
There are some issues with polarity and voltages appearing on the coil (the arc essentially shorts the NST to the HV terminal of the coil, so you get the voltage of the NST back through the auto coil..)
I don't think magnetic quenching is needed.. Run compressed air through the gap so you get cooling AND quenching. You'll need the cooling in any case. With a triggered gap, you can run a fairly large spacing (that 40kV pulse from the auto coil helps...)
A friend suggested using water instead of air as the flow medium (sparks will jump through water as well as air), but there are enough practical problems that I haven't explored that. Air isn't particularly messy when it spills.
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