Speaking of small Tesla coils -
One of my very first was made out of junk (I didn't spend a penny on it) and it stood only about four inches high. It used wire from an old microwave oven fan motor wound around a toilet paper tube for the secondary, and there was no topload. The primary consisted of just a few turns (4-6?) of bare copper ground wire removed from a section of 12-2 Romex residential cable, and it was set up on bottle caps at the base of the secondary. The capacitor was a single beer bottle wrapped in aluminum foil and filled with salt water. The capacitance measured about 0.5nF, if I remember correctly. I used a static spark gap (I believe it was 6 or 7 sections of copper tube mounted next to each other on a hard plastic VHS case) and the whole thing was connected to a 9kV 60mA NST.
https://www.youtube.com/watch?v=xvIowPqcWek
Looking back, I realize that the fact that it worked at all was sheer luck - I did not do any math whatsoever when I built this coil and I had absolutely no idea what I was doing. Nonetheless this build really sparked my interest (no pun intended) in Tesla coil building and brought me to where I am today. Despite its horrible design and assembly, I'm still fairly proud of this little coil, though if I ever tried to replicate it I can guarantee it would never work the same.
Regards,
Matt Lewis, Fairlee VT
-----Original Message-----
From: Gary Lau <glau1024@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, Jan 15, 2019 8:09 pm
Subject: [TCML] Let's Get Small
With apologies to Steve Martin, I was hoping to inspire some discussion on
the small end of the Tesla Coil spectrum. Not to suggest it's easy but
everyone knows if you throw 10KVA into a coil, you're eventually going to
get some big sparks. Not much has been shared about the other end of the
spectrum.
Several years ago I threw together a palm-top sized coil powered by a yard
sale bug zapper transformer. Bug zapper transformers are built just like
NST's, current limited but tiny. Inspired by the recent Little Coil
thread, I dusted it off and made some primary coil tweaks and adjustments,
and finally got around to taking some pictures. The performance is OK-ish,
maybe 2" to a nearby screwdriver, but I was really hoping to get some
similar sized sparks just wandering about the topload. Yeah I have plans
to tweak some more, although such a small 4-turn primary is difficult to
adjust. Looking for that round tuit.
Well, I was hoping to hear other successes in the micro-sized league and
what might be attainable.
Pictures and a short video are at:
https://drive.google.com/open?id=1q83wHgtXXlpcKSobd8bXSQ1ZlmvlK3zp
Specs:
Power source: 4.8kV/8.7mA Bug Zapper Transformer, modified to remove the
potted built-in ceramic capacitor across the secondary.
Primary C: .0094uF/8KV MMC (5x 47nF/1600V)
Primary L: Helical 4 turns PVC insulated 18AWG solid wire
Secondary L: 0.84”D x 4.43”L x #38AWG – 3.37mH
Top load: Pine disk, turned on drill press to form .75” x 3.4”
pseudo-toroid, Al tape covered
Spark gap: Single cylinder gap, .020” separation
Performance: 2.25” to a screwdriver blade (very little tuning performed)
Regards, Gary Lau
MA, USA
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