On 09/24/2012 08:48 PM, Christian Hill wrote:
Hello. I completed and ran my first Tesla coil this weekend. Putting it together and having it work was a very satisfying experience. I am not extraordinarily happy with the results, however. It is powered by three 12kV NST's in parallel for 1.1kw of power. The coil form diameter is 4.5" and the winding height is 22.5". It is currently throwing several(4-7) small to medium size arcs. (8"-24"). A breakout point helps, but I still think it's under performing. My question is, how can I get a single larger arc? I've seen several 1kw coils outperform my 1.1kw coil. I spent much time on and carefully planned almost (read on) every piece of this coil. I have a simple adjustable static spark gap. I have a very close to LTR capacitor array (off by about 1.1nf) and the coil is as tuned as it is going to get. The RF ground is good as well, I pounded an 8' grounding rod into the earth. The topload is where I think I screwed up. Not only is it rather small for my coil (4" ring, 16" total), it is rather poorly made. By poorly made I mean there are many ridges in the foil tape that is wrapped around the dryer duct. To get a single larger spark should I construct a larger topload? Or should I attempt to smooth out the edges in the foil tape? What size toroid would you recommend? I am considering a 4" ring x 20-22" total.
Well it wouldn't hurt to make it a little bigger, maybe step up to six inch duct and shoot for a couple feet or more in diameter (this will change your tuning point if you change the toroid size). The multiple breakout points are indicative of either too small of a toroid, or a "less than smooth" toroid, or both.
Given the power you are putting through your coil, I can't help but think you would get better performance with a six inch secondary, without being on the edge of flashover with a 4.5".
To make a smooth toroid, you "stitch" the ducting sections together with some wire (or carefully tape them together, then coat the entire thing with a lightweight spackling (I highly recommend Red Devil "Onetime").
Use some drywall sanding screen to smooth it, and apply an additional coat until it is round.
After the spackling is fully dried (plus an extra day or two), apply several coats of polyurethane until the spackling is sealed, then lightly sand until it is smooth.
When the poly is fully cured (several days or more at a warm temperature), cover the whole thing in strips of aluminum tape, carefully burnishing each strip as you go, and then again when you are done.
It is a bit of work, but you will end up with a very smooth toroid for your efforts.
Here are some pics I took when I made mine (6.5" x 30", for a 6.5" coil); I used black poly tubing, but the process will be similar with aluminum ducting:
http://imgur.com/a/D3SjZ#0 Jon _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla