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Just wound my first secondary

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speakerguy79

Mon Mar 16 2009, 09:57PM

Registered Member #1460 Joined: Thu May 01 2008, 12:45AM
Location:
Posts: 19

I just wound my first secondary. It's 3.5" x 15.25" wound with 24AWG magnet wire. About 700 turns for 9mH. Does anyone know what my self resonant frequency of the system will be about without a top load? Not scientific or anything, just ballpark if anyone has used a similar secondary. I have no idea what the parasitic capacitance will be.

Arcstarter

Mon Mar 16 2009, 10:04PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

It would be about 663khz.

speakerguy79

Mon Mar 16 2009, 10:17PM

Registered Member #1460 Joined: Thu May 01 2008, 12:45AM
Location:
Posts: 19

If I add a toroid + breakout point (a sharpened tungsten welding electrode), would it drop the resonant frequency? What about when I am drawing a continuous arc from the breakout point?

This is intended to be a small solid state tesla coil. I wanted the primary to be a little longer but the dang wire kinked on me and got all messed up, so it's 15.25" instead of 17" or more. My half pound of wire still had some left on the spool.

speakerguy79

Mon Mar 16 2009, 10:18PM

Registered Member #1460 Joined: Thu May 01 2008, 12:45AM
Location:
Posts: 19

Oh hey! I see you are in Beaumont. I am in College Station btw.

Arcstarter

Tue Mar 17 2009, 02:57AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Haha really? My brother goes there :). Going to school for process and operating, hopefully getting a job with Motiva. Hehe.

Anyway... Topload will lower the resonant frequency, drawing arcs will lower it, the higher the primary is in relation to the secondary the lower the res freq is, the surroundings will change it. That is why a continuous oscillator is not so great for use with drawing arcs and the like. A feedback based oscillator is much better.

speakerguy79

Tue Mar 17 2009, 06:04AM

Registered Member #1460 Joined: Thu May 01 2008, 12:45AM
Location:
Posts: 19

I was planning a feedback based design based on a current sense transformer on the primary coil with either a microcontroller (which I'd like to avoid due to all the ambient noise and whatnot) or a pure analog feedback system. Then I get on here and see people are already doing feedback systems... so there is a lot of information I need to read first. No need to reinvent the wheel. I just bought the two books from Eastern Voltage Research tonight and will be doing a lot of reading. I am a degreed electrical engineer (BSEE UT '03) and have worked as an embedded electronics engineer for several years. I quit my day job last April and set up my own shop (Tek DPO scope, OKi rework station, lots of development goodies). Bad move with the way the economy has gone but I'm having fun. Don't ask me how I ended up in B/CS after being a UT grad. Long story.

Are there ever any Tesla coil / HV gatherings in the area? I would be very interested in anything like that. A&M is having a Physics weekend thing next weekend that I'm sure will have lots of neat displays.

Anyway, here is a pic of what I've done so far. How much polyurethane should I use to seal it? I have put on two medium-thin coats so far.

Sulaiman

Tue Mar 17 2009, 05:58PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Next thing to do is coat the secondary with varnish/paint/epoxy or any insulating coating.
It's not for insulation - it's to hold the wire in place when things heat up.

Also looks nicer.

Arcstarter

Tue Mar 17 2009, 07:36PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Are there ever any Tesla coil / HV gatherings in the area?

Well, no. Hehe, i wish there was one, but nope. There is no good electronics stores around here that i know of.

But bad onto the subject. My small/medium secondary has 11 thick coats of Minwax fast drying clear gloss polyurethane. It is VERY good with all of that poly, when i pull the output wire, it oes not move unless i pull hard. In other words, the coatings are thick enough to ensure it will not get pulled and come unwound.

Also the insulating properties are good :).

All of his solid state tesla coils are very good, including drsstc's. I would recommend sstc before drsstc though. A good one is the mini sstc. It is run purely on the antenna feedback, there is no startup oscillator. Make sure you always look at the bottom of the page to make sure you use the right schematic.

My latest audio modulated sstc was a PLL:

I used that basic schematic, with a bunch of modifications :P. This one is harder to get working right though.

Mads Barnkob

Tue Mar 17 2009, 08:03PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

You can find some good tools at JAVATC and JAVAMMC at

And there are some good javascript calculators at

With these two sites you can calculated about everything you need for a tesla coil :)

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