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Re: HV wiring
Hi Kent,
I build a lot of classical Tesla coils (relatively thin long, not
magnifier types).
You will see corona off the last turn with that small top capacitor.
Along the length of the coil, each turn is in close proximity to a turn
of similar potential - that, and the curvature of the coil suppresses
discharges from the side of the coil (unless there is a nearby ground).
I've tried a number of things to try and eliminate it (since it does
waste some power). The only things that seem to work are insulating the
entire coil in oil, or using a large top terminal. Oil is a real pain,
but works very well.
A large top terminal, if it is close enough to the last turn of wire,
effectively over-shadows the last turn and suppresses corona.
Large top terminals, ala mixing bowls, or toroids (from aluminum duct)
are the only practical way to deal with it. But your driver has to have
enough power (watts) to drive the added capacity and still break out an
arc. That's when you begin to see the white hot arcs everyone seems to
try for.
I tried spacing the final (top) turns at various spacings, and even
tried a logrithmic spacing of the top turns. As soon as the spacing of
the turns opens to about 1/4" (on a three inch diameter) the corona
starts breaking away.
What may be an elegant solution is something I saw in a publication (but
haven't tried). Someone has built a top terminal using a plywood
support to hold what looked like 1/2" copper tubing rolled into a
generally spherical shape for the top terminal as well as the final
turns of the coil. The sphere over shadowed the top turns by about one
diameter of the coil. The tubing seemed to be spaced at roughly two
diameters apart.
Note (list): anyone have any experience with a coiled tubing top
terminal? Does it work? How was it made?
Insulating coatings help, but it takes something like a big gob of RTV
rubber around the entire turn and you still have to deal with the lead
to the terminal.
Attaching the top terminal? any way you want. It doesn't even have to
be a good connection, 100KV always finds a way to get where it wants to
be. I like experimenting with a lot of different coils, so I use end
caps of PVC or Plexiglas and just set the sphere or mixing bowl on the
lead wire. For toroids, I cut a series of gores (truncated triangular
shapes) from aluminum flashing and glue them into a huge, shallow funnel
shape that goes into the center of the toroid.
Take care
bob