Tesla Coil 3

A Rather Small Tesla Coil


This project was born after I found and bought a curiously thin AWG 40 (0.08mm) wire from an electronics shop. Having achieved rather good results with my Tesla Coil 1 and Tesla Coil 2, I thought it would be a great idea to build a ridiculously small tesla coil! I also submitted this as part of a thread in the 4hv.org forums back in end 2004 / early 2005, when there was a little competition going on to build the smallest Spark Gap Tesla Coil possible. I named this project ARSTC - A Rather Small Tesla Coil.

[ Note]
I always wanted to post a little page about this project, and some 9.5 years later, I've finally done it! Perhaps one day I'll try my hand at building another tiny coil sometime. Enjoy!

ARSTC Specifications (I modeled this is JavaTC some 9.5 years after it was constructed!):

- ~10kVDC input from a flyback transformer
- ~5 x 29mm pen refill secondary
- Wound with ~330 turns of AWG 40
- 5 or 6 turns of normal 24AWG wire (primary)
- Four 680pF 2kV ceramic capacitors in series
- Approximately 6.9 x 14mm 'toroid'
- Just about 1cm sparks
- Secondary resonant fres: 20.4Mhz
- Primary resonant fres: 24Mhz
- Spark length - 10mm

Back then I didn't really do any modeling for the coil, but the fact that it made ~10mm sparks was quite amazing, even though the flyback transformer acting as the power source made bigger sparks than the coil itself!

 10 Dec 2004 

A Rather Small Tesla Coil

December 2004

I started the project by finding the smallest secondary form I could find. I originally wanted to use a pen as a coilform, but that was too big, so I decided to use the inner tube of a Pilot G1 or G2 pen (I can't recall which one), but it was 5mm in diameter. Then with the help of a magnifying glass, I starting winding the insanely thin 40AWG wire! The first time ended in disaster and I had to restart, but the second time went well and I completed the coil in just around half an hour.

With the secondary coil complete, I varnished it to protect the coil, and set up some test primary coils as a proof-of-concept. For the capacitor, I used a self-made Lynden Jar using salt water, aluminum foil and a small glass vial. First light was produced using simply my crocodile clips as the primary coil. For the power supply, I simply used my flyback high voltage source. Needless to say, I could not tell what the voltage or current was. Then I formed a 'toroid' out of aluminium foil. But would it work?

First light is always a milestone event! Even though this coil produced only 1mm sparks, it was working as a Tesla Coil, making sparks without electrical contact with the primary circuit! However, I thought it was a bit ridiculous since the flyback power supply was making 10mm sparks - 10x longer than the coil it was powering!

I started tuning it by adding more primary turn, and the result was a coil that made sparks about 5 to 6mm long. I eventually settled for a cute-looking primary coil held in place with hot glue. Finally, I used two brass screws as a spark gap! The coil now made 5-6mm sparks. 


29 January 2005

I had some spare ceramic capacitors lying around so I thought that maybe I could try to improve the performance of the coil.

In addition, I added some more projection for the secondary coil by shrink-wrapping it with clear heat-shrink. I used four 2kV 680pF ceramic capacitors as the resonant cap (in retrospect this was just guesswork - I was lucky that the coil actually worked!), and a new cylindrical primary was made via a few turns of wire and everything was secured via hot glue. I did this to increasing coupling to the coil. How would the new design fare?

Not only was it producing bigger sparks than before, it was also producing a small but stronger electric field enough to illuminate neon bulbs a few centimeters away with no difficulty. Compare how much brighter the neon bulb lights up!

What I thought was especially nice was the extremely delicate 20+Mhz spark forming at the top of the toroid, similar to that from a flyback transformer, but very wispy and looked almost quiet (of course with the buzz of the spark gap, I could not verify this). But it was very fascinating for sure.

I submitted it to the forum's competition and I believe at time of posting, was by far the smallest Tesla Coil. I believe that this forum was at the time (and even today), the forum for Tesla Coils (for English speakers), it could have been the smallest Tesla Coil in the world! Someone soon built a very slightly smaller coil, but I am happy to have got this working! Perhaps next time, I'll try building a tiny coil like this, but with the power supply integrated together!

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(c) Gao Guangyan 2024
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