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New Spark Gap demonstration coil

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StevenCaton

Sat Apr 18 2009, 12:05AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Hello 4hv members.

The twin spark gap system I built took up too much room in the garage, so I decided to take the parts from the twins and build a single SGTC. The goal with this project is to create a coil that's always ready to fire up, for demonstrations for family and friends. I've been gaining experience with tube coils and solid state lately, but those projects are always half way taken apart, being fixed, modified etc. (for now at least)

The four toroids are temporary. I'll replace them with two large ones soon, as the current four look a bit goofy. So far, I've got the best results with four toroids. Tuned coil with one (bad output) two (better) three (really good) four (Run!!!)

I haven't tried five though. It seems that with spark gap coils, more toroid is usually better. I think people underestimate often and have too little capacitance.

I reached full power this morning when I was tuning it, and racing sparks started to set in at 110 volts AC input. There were some very wispy flashovers also. I'll raise the secondary up 1.5 inches. Hopefully that might stop the racing sparks too. At 110V AC input, the coil starts hitting the ceiling in the garage, so this coil can only be run outside from now on. (I wouldn't want to start a fire!

)

Quick question about LED's. I had a neat looking string of 8 green led's around the outside edge of the spark gap box. After the first couple tests of the tesla coil, the LED's died. I'm assuming the coils electromagnetic field is inducing too much voltage across the led's leads. Same thing as lighting up a flouro tube Usually about 9 volts will make an led burn out.

So question is, do you guys think the Led's would be likely to survive if I put them INSIDE the spark gap box. (which is covered in plastic)
Chris Hooper usually has a bunch of leds on his coils and they seem to survive. He must rout the wires inside the coil, unexposed to the open air.

Next project will be my first DRSSTC.

Firefox

Sat Apr 18 2009, 03:46AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Looks good, Steve! How is your primary coil wound/tapped? Also, you could also take the secondary out and coat it with more varnish/epoxy. That should help with your racing arcs, though you may still have to raise the secondary.

Arcstarter

Sat Apr 18 2009, 04:04AM

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

That looks very good indeed! That primary looks awesome! I made a primary like that too, but it turned out to be steel, not aluminum. Oh well.

I cant wait to see some sparkz, looks like it is a great performer!

StevenCaton

Sat Apr 18 2009, 04:38AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Hi guys.

Just got back from the garage after a bit of tuning.

Raised secondary 1.5 inches, at 90% input power, racing sparks are not there.
Hopefully racing sparks will not occur at 100% input power, but I haven't made it up to that point,,,, still more tuning to do.

Also, you could also take the secondary out and coat it with more varnish/epoxy. That should help with your racing arcs, though you may still have to raise the secondary.

Its got quite a bit of polyurethane on it. I may have to do additional coats if I get racing sparks at full power. Raising secondary seems to have worked,,,, don't know about Full power though.

With 93% input power, and rough tuning (nothing too fine yet) I'm getting 46 inches out to a spherical target. Sparks are hitting the ceiling though, and they look really long, closer to 50+ inches.

As I said earlier, I really can't do any more tuning in the garage. I'm scared I'll set the ceiling on fire.

However, I can't go outside at the moment, as my dad is hosting a party with 40 guests outside. I wouldn't want to cause too much of a stir.

Tomorrow, I'll tune it up to its max. I still might add another toroid just to see if I can get even more output. I wouldn't doubt it

I'll make a guess right now and say this coil will do just over 50 inches when complete. (51-55 inches maybe,,,,,,55 is being really optimistic I think)

I cant wait to see some sparkz, looks like it is a great performer!

Will post pics for sure once coil reaches it max. Will be pushing coil out of garage tomorrow night for full power and extensive tuning.

How is your primary coil wound/tapped?

Primary is brass weatherstrip. .25 inch thick polyethylene foam goes between the strips to maintain spacing. Tap is two stainless steel alligator clips I believe. I was worried they would get hot but they are only warm after a short run.

The fact that the primary is BRASS brings about a question. Do you guys think that I should change the primary to Copper in the future. I'm not really sure how much of an increase in spark length it would get me. Lowering primary resistance is apparently critical in a drsstc, but what about spark gap coils? Any guesses.

coillah

Sat Apr 18 2009, 09:20AM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

Well... I am not an expert, but if I had to guess, having a higher resistance for your primary coil will mean lower current. Thus, lower power output, since the amount of charge moving through your primary is proportional to your magnetic flux which is a direct factor in how much energy is transferred between primary and secondary.

I have been into coils for about a year and I can hardly remember anyone who recommended anything over copper.

Otherwise, that thing looks like it can really cook! Lets see some sparks!

Dalus

Sat Apr 18 2009, 09:55AM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

The performance gain that you would get from switching to copper would be minimal. SGTC's use a relatively low primary current compared to DRSSTC's I wouldn't expect more then 1 inch gain in spark length. In short not worth the trouble and cost unless you really want to fully optimize your coil and go all the way.

StevenCaton

Sat Apr 18 2009, 04:37PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

OK, Dang racing sparks are a problem and need to be fixed. They are preventing me from reaching full power. I need to get rid of them, as this coil is supposed to be able to run all the time with high reliability for demonstrations.

TO SOLVE RACING SPARKS....

Someone suggested coating the secondary with even more polyurethane to solve the problem, but I have another idea.

What about winding a slightly taller secondary. (4 inches taller) Shouldn't this spread the voltage out a bit more?

Also, if I was to wind a taller secondary, should I go with a slightly larger gauge wire, or slightly smaller gauge wire. Which would be better to stop racing sparks? Too hard to say? (current size is 24 I think) I will also coat the new taller secondary with twice as much polyurethane. What do you guys think of the plan.

Mike

Sat Apr 18 2009, 04:40PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Racing sparks happen when you have overcoupling. To fix it most people raise the secondary up to change the coupling coefficient. Try this before spending time winding a new secondary.

Hazmatt_(The Underdog)

Sat Apr 18 2009, 07:01PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Yea, you're way overcoupled there.

I made the world's first parabolic primary just for fun, and it was extremely overcoupled. I had racing arcs even at the middle of the coil!.

You need to raise that coil about 4" up.

StevenCaton

Sat Apr 18 2009, 07:22PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

OK, I'll raise it up a bit.

getting 47-48 inches right now at 105VAC input.

Hopefully with raised secondary and full power (120VAC) I'll get 50+ inches

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