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On 7/4/18 11:40 AM, David Rieben wrote:
Hi Phil,
My deepest condolences for your loss. I know it's JUST a secondary coil,
but as a fellow coiler, I most assuredly feel your pain. On the bright
side, at least you did manage to capture some truly spectacular footage
of this secondary coil mishap. I have had this happen on rare occasion
with the operation of my big coil, though fortunately, none of my
mishaps turned out quite that severe! Only once did I actually have to
repair some damage to the side of my coil and was able to get it back
into full functioning mode via the repair. Since I must operate mine
outside, I did have one occasion where the wind actully "blew" one of
the streamers back into the side of my secondary coil, too. Lesson
learned - although refraining from outdoor operation during rainfall is
an obvious good rule, non-starters in windy conditions are also well
advised.
I suppose this is a risk, that although may be small with a well-tuned
and efficiently operating coil, is never completely absent. :^/
I wonder if we could figure out a way to segment a large coil
vertically, so if a segment gets damaged, you can just rewind that
segment. Just off the top of my head, I'm thinking about something like
segments with a hundred turns or so. Could we come up with a way of
making the connections in a "good" way. I'm almost thinking about how
you using field grading rings on a Van de Graaff. You don't want a
complete shorted turn, but you could terminate the winding in some sort
of flat terminal on the "mating face" of a segment. You'd stack the
segments, and then put some compression on it (threaded fiberglass rod?)
The other idea that comes to mind is if there is some way to "spread"
the energy of the secondary strike.. Say your secondary were coated with
a resistive (but still conductive) coating. Would that spread the
current density enough to prevent burning through the insulation? Or a
dissipative tube covering the secondary - not enough to "load" the
secondary, but enough to "take the hit".
OR, what about a second helix, space wound, that extends the length of
the secondary, with some suitable resistive conductor, so the voltage
profile matches that of the secondary (so no protective helix to
secondary arcs), but so it doesn't enter into the resonant circuit. The
protective helix would be mostly capacitively coupled to the secondary,
establishing the voltage.
What about something like a helix wound with wire, but with small gaps
along the length.. the gaps don't break down normally, but if a streamer
strikes, the gaps break down and provide a conductive (but lossy) path
to the base.