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Registered Member #3768
Joined: Tue Mar 22 2011, 12:46AM
Location:
Posts: 107
Hello, I tried running my Tesla coil and nothing happened but the spark gap sparking. I have this secondary, and I have a 9.3nF capacitor bank to go along with it and I am powering it with a 15kV NST with protection filter and protection for the mains power. I have the spark gap blown by a fan. I should mention that I couldn't find a very good RF ground where I was doing this, so instead of using the building's ground I drove several 1 foot long rebar into the ground and wired that to the bottom of the secondary coil. I should also mention that the primary windings are not the 1/4inch copper tubing that I bought, because I could not get it to curve so it got all kinky and bendy, so I replaced it with insulated wire.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Is the "spark gap - capcaitor - primary" a series circuit, or do you have the SG in parallel with the cap? I have always had better results with a series circuit. Even with a poor ground connection you should still get some sparking if it;s properly tuned. If everything is connected up right I would say it's a tuning problem. How many turns on the primary? What is the secondary coils res frequency? Hope you have a 3-point safety gap across the NST output or that transformer is not going to last long.
Registered Member #3768
Joined: Tue Mar 22 2011, 12:46AM
Location:
Posts: 107
I have the spark gap in parallel with the NST and then the cap bank is in series with that to the primary coil. I have this as protection on the NST I think it might also have to do with the bad fact that I am not using what the person who sold me the secondary coil said to use for the primary winding, I am using just some thickly insulated wire...
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
ok - so that's basically a series circuit. Should work just fine. I am not sure the wire as opposed to tubing would stop the coil from working. May get better results with the tubing but I doubt that's the reason you get nothing out of the coil.
Watch the coil in a dark room (cover the bright spark gap). If you start seeing corona discharge somewhere on the secondary winding you have mismatched res frequencies. Try adding or reducing turns (one at a time) and see what happens. Of course if you have an oscilloscope and signal generator you could test with low voltages and tune it that way.
Not sure what secondary current NST you have, but make sure the impedance of the NST output matches that of the 9.3nF cap at 60Hz. If they are not matched you will not get maximum power transfer to the primary circuit. Probably not your issue, just a side note.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I have in the past, The problems can arise when the secondary arc hits another grounded object and tried to find a path through your house wiring back to to other end of the secondary. Try and keep ground strikes to something connected directly to the base of the grounded coil. I think that's how most of the guys run their solid state coils.
Registered Member #3768
Joined: Tue Mar 22 2011, 12:46AM
Location:
Posts: 107
Ok, but do you think that the insulated wire will work though? We tried a bunch of stuff and it didn't work... What should the spark gap length be for this coil?
Registered Member #5300
Joined: Thu Jun 14 2012, 12:00AM
Location: California
Posts: 31
I had similar problems when I first fired up my first SGTC. Our capacitors were messing up for some reason, and our spark gap was on the order of four inches. Make sure you're on the millimeter scale. We eventually got better capacitors and used a parallel circuit. I highly recommend the parallel circuit.
Another, main issue we were having was grounding. We originally had a two foot iron rod pounded into wet soil ground, which I think should have been fine but didn't work for whatever reason. We got a legitimate grounding rod from Home Depot and pounded that suck 6 feet down.
Finally, something that I've made a habit out of now since it works VERY well is using a handheld grounding rod. I hooked a separate aluminum rod up to the iron rod shoved in the ground, and whenever we turned on the coil, I started the rod very close to the toroid and pulled back to draw out the spark.
As it was said above, test in a dark room. It really helps to see the spark. The first time I got sparks, I was so out of tune and using the wrong capacitors that the spark was half an inch--I never would have been able to see it in the daylight.
Can we get pictures of your setup? What kind of primary coil are you using? I went with a flat, pancake style. Am I right in imagining yours as a helical, insulated wire coil running up the secondary?
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I have built many SGTCs with insulated wire and they work. That is not your problem. I always tried to keep the spark gap just under the open circuit gap for the NST. you can get really high over-voltages on the primary circuit when resonating, which can put the NST and/or capacitors at risk. Photo of the whole setup would be helpful.
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