Mini-coils?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: The MCP <ejkeever-at-comcast-dot-net> 

This was a cute little thing I thought about a while back. I was considering
taking some batteries for power, one of those little step-up switching
transformers you find in portable fluoresent lights, and using it to power an
ultra-tiny tesla coil (secondary maybe 1-2 inches tall, .5 or so dia).
Methinks it'd be a cute demonstration coil.

The problem I see is creating a good secondary. If you shoot for 750 turns,
that comes out to 350 turns per inch, which would require *42 gauge* magnet
wire. Not only will you be using something far smaller than hair and rather
ductile, but the 100 feet of wire used would have almost 160 ohms of
resistance (The same as my coil). I can't imagine this having a good effect
on performance. On the other hand, if you can stand to settle for a mere 500
turns on the secondary :) then the resistance drops to 86 ohms.

I went to the new version of JavaTC, and it says that this baby coil will
resonate at 4.86Mhz, and has .91pF of self-capacitance.

I did a little theorizing on the primary coil, and (if you use a 12.5nF cap)
it should be a single 1-inch diameter turn at the center of the coil.

I haven't quite figured out what to use for a power supply (Current-limited +
wall plugin or batteries + mini switching supply) and I was wondering if it
would be possible to use a high-speed power transistor to switch it.

Well, that's my cute idea for the day. My idea for the setup is to keep the
electronics in a box, about 4" long, 2" wide, and maybe 1" tall. Then mount
the coil horizontally above that, and just rise the 1-turn coil out of the
box. Attach the ends of the coil to a pair of little balls on movable mounts.
BANG, instant miniature tesla coil. Or no?

The idea occured to me when all my friends were amazed by the coil I already
built (No one recognised the term "tesla coil" so I ended up calling it a
"lightning machine." Sigh...), underperforming as it is. So why not make a
cute little coil to play with?

Plus, since it is (except for the transistor) a real tesla coil, you can use
it to explain how they work. Ok, I'm done talking now.