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My Solid State Tesla Coil

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Wolfram

Wed Aug 20 2008, 04:43PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Not very much new unfortunately.

I have tried running it with fullwave rectified and smoothed mains, at 20 primary turns. I didn't dare go any higher than halfway up on my variac, as there was corona from all sharp objects nearby and gas discharge tubes were lighting up in the shelf beside me. It also managed to crash the wireless router and the ADSL modem. Nothing that a reboot didn't fix though.

I have used the coil at full power with 4 primary turns and 250V RMS halfwave rectified input many times the last months, often many runs a week, and so far it has been completely reliable since April. I must admit that I haven't run it for prolonged periods at full power, due to some thermal issues. The main problem is that I use quite small heatsinks on the FETs. This problem is easy to fix but I haven't gotten around to it yet, as I seldom need to run it longer than half a minute.

I've also tried to use it with a PIC-based MIDI musical interrupter, but had some trouble with the coil messing with the PIC. This was probably due to insufficient screening of the interrupter and it's direct connection to the coil probably didn't help. When I get the motivation, I'll try again, but I'll optically isolate the output from the inverter. This is not very high on my priority list.

Anders M.

LithiumLord

Tue Feb 23 2010, 02:12AM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Guys sorry for archeology but this is where my question fits best. Having a look at the nice results in here (and also having moved to my gf ;) ) I decided to try out a smaller secondary with my old driver being a bit optimized (made the bridge somewhat more compact, removed schottkys though as the research proved that there should be nothing wrong in running with UFs alone, and added the overcurrent protection, also trimmed the deadtime a little and made an improved feedback, all details later on should I get something interesting soon enough). As for the secondary, I just wound one with a 0.3mm (at least it looks so) copper wire on a 25x8cm tube, used the old 18x8 top load and with all that rigged up I tried to push it somewhere. Well, all gone bad, apparently :) The first test was with only three primary taps (didn't care of the safety as got the OCP). Didn't push above 100vdc or so, gave me like 8cm spark. Hmm, weird. Rigged everything properly and wound 11 primary turns, then cranked it all the way up. Nothing - only neon light flashes and a tiny corona. Now just have no idea what's wrong - probably yet unlikely there may be an issue with the deadtime too high or whatever, yet that's still weird. With 3 or 4 turns I get some short streamers on the lower voltage, and their length is highly dependent on the coupling (best is when they are tight and placed at the very bottom of the winding). Anyway, 3 turns do not feel right no matter what. So, why isn't the thing ringing up? Is there anything I missed like lags etc, or I just can not proceed with this secondary?

[add]nvm looks like I figured out. With a secondary running that high on frequency higher coupling is not an option as it will get the Fres even higher. Low coupling will be ineffective as will put even more stress to the switches so therefore just one thing to learn: thick wire is not an option no matter how much pain is it to wind with a thin one. By now I got an xformer dismantled so stripped down my secondary and will now be rewinding it.

teravolt

Wed Feb 24 2010, 04:11AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hello Anders M., what ever happened to this coil? I see that the primary is using cat 5, do you remember how the primary was inter connected and connected to the bridge. this coil is amazing in its simplicity and efishency. its to bad the thread ended before the project. would you be willing to poast a scematic. thanks Nathan B.

Wolfram

Mon Apr 04 2011, 09:49AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Sorry, didn't see your post until now. The coil is currently in bits, but I still have everything. I brought it with me to the Cambridge Teslathon in 2009, and got it working there after borrowing a suitable variac. One big mistake I did was going back to a single heatsink and sil-pads to make it more compact (I needed to bring it with me on the plane). This of course brought back the problems I had earlier with MOSFETs overheating when running at 3kW. I could of course tap it back to 10 turns to limit the power, but that wouldn't be too interesting, so the Friday I kept the runs short, and on the Saturday, I blew a few MOSFETs when trying to see how long I could run it, some people were filming it, and I wanted to give them a proper run for their money.

Here

is a film from the event.

I gave away the bridge/heatsink, to make more room in my baggage, and brought the rest of it back home with me. I haven't really done anything more with it since, as I have worked on other projects. When I get back to it, I'll surely make a new bridge with separate heatsinks for each MOSFET, and see if I can push it any farther. With some more beefy MOSFETs or suitably fast IGBTs, even higher powers should be possible. Interrupted coils can surely get much more sparklength per kilowatt, but the raw power of many kilowatts being burned off in a half-meter spark can be quite a show.

3l3ctrici7y

Mon Apr 04 2011, 12:01PM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

Anders M.; Those videos are just incredible. That is a fine looking sstc :)

For measuring current, you can simply take some wire of known ohms/length, cut it to length, and measure the voltage across the wire when connected in series with the load. For quick computation, you can use the calculator at powerstream

I have built a number of shunts this way. I used a long section of 22ga wire giving me 10mV/A for precision measurement of AC current from the mains. It was so long I bent it in half to minimized its reactance*, then wrapped it up. Another one I built, I used 4 feet of 4ga. I used this for measuring electric arc welding current. It drops 1mV/A, and at 400 amps, that 4' section of wire is dissipating 160 watts.

*not that it would be much at 60Hz, but still; it's a measurement instrument.

radhoo

Thu Apr 07 2011, 10:24AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

You've got some impressive sparks there, congrats on this project!

Did you continue working on it? Would love to see some news.

Wolfram

Thu Apr 07 2011, 10:38AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Not much news, unfortunately. I don't think it will take a lot of work to make it functional again, and I plan on doing that one weekend when I'm at home. I don't feel that I've gotten any good pictures of it so far, so I need to get this fixed. The plan was to add reverse phase angle control to it for lower power and/or longer sword sparks, but Steve Ward proved that there's a much better way of making long sword sparks with his QCW, so I'm considering making it into a QCW coil when I have some time to work on it.

Goodchild

Thu Apr 07 2011, 03:06PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Ill tell yeah the QCW is a hell of a lot of fun and well worth the effort. I just got mine working a little while ago.
5593516579 881060d631

teravolt

Fri Apr 08 2011, 02:40AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

beutiful sparks Eric, and Anders. I dont know if the jury is still out or not on that are the sword sparks are because of the type of modulation feading the teslas or its resonant frequency of 350 to 500khz? Steve Ward said it is about growing the sparks. Boath of you are using a ramped or unfilterd recified AC. So I put it to you do you think sword sparks could be generated with a tesla with a lower Fres or is it a product of modulation?

Goodchild do you plan to do a thread in your coil?

Goodchild

Fri Apr 08 2011, 05:52AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

The sword sparks are a combination of resonant frequency and modulation of the bus voltage. You need a rather high resonant frequency to achieve "perfect" swords with no branching in the range of 350KHz and up. Not saying sword like sparks don't exists at lower frequency, but there is more branching and they are not as strait.

The next big thing after frequency is modulation of the bus voltage. The idea is to grow the streamer over a long period of time. The longer the spark the longer you have to grow it for. If you try and grow a big spark to fast it will just splinter and branch out.

I modulate the bus of my QCW with a synchronous buck converter that is able to produce a ramp that can be 5 to 25mS in length and peak at close to 400VDC. Just to give you an idea; a 4 foot spark needs about a 15mS ramp up time and a peak voltage of about 250VDC (spark in photo is about 4 feet).

I don't think I will be making a project thread for this coil, but if you are interested you can look at my flikr page

it has a lot of the details of my build.

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