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Beginner tesla coil, doen't work

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LAN_403

Dash_Riprock

Sun Apr 06 2008, 06:13PM

Registered Member #1431 Joined: Sun Apr 06 2008, 04:59PM
Location:
Posts: 6

This is (obviously) my first TC. Basically, everything seems to work fine except, well, the entire point of all this effort. The capacitor holds charge, the spark gap fires, and no charge builds up on the spheroid. There is some voltage about half way up the secondary, just barely enough to see at night and can be faintly heard, but none near the top of the column. Ill try to be a specific as possible listing the parts.

This obviously came out blurry, but there isn't too much to see anyway:

power supply: 10kV, 30mA AC CoolNeon NST.

Rectifier: four 30kV, 30mA rated diodes.

Filter: about 60 winds of transformer wire. Probably doesn't do much, but hopefully better than nothing.

Yes, those are legos.

Spark gap: basic static spark gap. It seems to work fine and makes alot of noise when running. Im not sure if this is normal, but it is still cool to the touch even after 30 seconds of running.

Capacitor: 3 1.5L wine bottle capacitors in parallel, filled with baking soda solution and a small amount of motor oil and wrapped in aluminum foil. Im not sure how much charge they hold, but they do make a spark when discharged after running. I made another out of Plexiglas sheets and aluminum foil, but I want to get this working before I try using that.

Primary: made with stripped car battery wire (probably overkill, but I didn't have anything else available) Note: Avoid stripping this stuff with a razor at all costs!!

Secondary: 80ft. of 22ga. wire at the bottom, 150ft. of 26ga. wire in the middle, and 400ft. of 30ga. wire at the top (Radio Shack only sold coated wire in packs of 3) for a total of about 950 winds around a hard cardboard poster tube and wrapped in a single layer of masking tape to protect it (I didn't have varnish...). The top consists of 2 metal bowls, and the bottom is grounded via spike in the ground.

The resistance from the ground wire to the spheroid is about 50 ohms. I calculated the theoretical value to only be about 10 ohms, which does concern me, but i can't imagine that this is the main problem, because Im getting no results at all.

Ive been trying for a while and cant find out whats wrong with this thing, so any help would really be appreciated. Thanks in advance.

Ultra7

Sun Apr 06 2008, 06:47PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

Okay, lets start from the beginning.

Is that a switch mode Neon transformer?
I. E. is it big and heavy and made of metal, or is it light and mostly plastic?
I have only worked with the big, heavy, all metal NST's and have heard that switchmode (light and plactic) don't work.

Do you need rectifiers to run the coil?
I use purely AC with my TC.
Straight out of the NST, into my Terry Filter, and to the spark gap.
I don't use Diodes, but that doesn't mean it won't work.

Basically, My TC schematic looks just like this.

The differing gauges of Magnet wire and how they are spliced might be an issue.
I figure you might be loosing some juice with the differing gauges and the fact that your secondary is 3 pieces of wire spliced together.
Also you said that you get corona in the middle of the coil? I would recheck that splice point.

How are you tuning your secondary?
The last pic looks like you have frayed wire coming from the cap to the secondary.

Oh, and welcome aboard BTW.

Dash_Riprock

Sun Apr 06 2008, 07:10PM

Registered Member #1431 Joined: Sun Apr 06 2008, 04:59PM
Location:
Posts: 6

Thanks for the quick reply.

The transformer is bout 7" long and weighs a little over 2 pounds. The cover is plastic.

I'm not sure how the circuit can work with an AC output from the transformer. Wouldn't the capacitors never charge, because they would only get partially charged before the current would reverse, causing them to discharge? That seemed to be the case for me before I made that rectifier, after which at least the spark gap fired. Other than the rectifier, yes my circuit does look like the one in that diagram.

The secondary is actually 6 pieces of wire. The ends are stripped of their coating and soldered together.

As far as the frayed wire on the primary connection, that is just my temporary solution until I get this working. It's hard to see from that picture, but the wires are meshed into each other. When Im actually using it, I make sure the connection is very solid.

And about the corona, sorry I wasn't clear about that. It only does anything when I hold a grounded wire right next to it. It doesn't do anything with just air. Also, it isn't at just one point. It sort of fades in near the middle and fades out near the top and bottom.

Ultra7

Sun Apr 06 2008, 08:19PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

Hmmmm. . . .

Sounds like you have a switch mode NST.

My circuit is purely AC.

I'm not too keen on DC resonant charging tho.

ArcLight

Sun Apr 06 2008, 08:40PM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

Legos and a milk crate very creative, kudos.

I've never tried an electronic neon power supply, but my understanding is that they will not work for Tesla coils. The smallest NST that I have is a 12kv 30ma. unit and it weighs 20lbs.

Your sparkgap would make a great safety gap but it desperately needs forced air (lots of air, like an air compressor) to blow out the arc if you want it to be a main gap. When operating, the gap should hiss like an arc welder, if it bangs like a very fast machine gun, you are probably way out of tune.

All of my coils to date have been MOT or NST and I have never used any diodes.

My 3" AC, static gap coil in action.

Good luck, ArcLight

Edit: I see that while I was composing my response Ultra7 posted so mine is redundant. Oh well, that's what happens when ya get old and slow.

Coronafix

Sun Apr 06 2008, 09:59PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Get rid of the rectifier, without a charging choke it won't work.
For the theory of how an AC tesla coil works and choosing the right capacitor for it,
see Richie's page here,

Also you might have a break in your secondary wire, it really is best to wind it with one length,
but that's not to say it won't work as you have it, just make sure you insulate it properly.
Transformer is a problem though, but if spark gap is firing then it might possibly work.
Your gap looks a bit small, try opening it up, but put a safety gap on first.
Good luck.

Dash_Riprock

Sun Apr 06 2008, 10:00PM

Registered Member #1431 Joined: Sun Apr 06 2008, 04:59PM
Location:
Posts: 6

So you're saying Im boned?

I still dont understand exactly how an AC current can charge a capacitor... unless the capacitor is exactly the right size that it fills up and the spark gap discharges right when the transformer switches polarization... but I would think even a minuscule difference would create a beat frequency that would kill performance, unless Im completely misunderstanding this whole thing...

And BTW, the gap does fire fast enough that you cant distinguish between individual firings, so it just sounds like a constant buzz.

FireBird

Sun Apr 06 2008, 10:47PM

Registered Member #1104 Joined: Tue Nov 06 2007, 07:38PM
Location: Wisconsin, United States
Posts: 34

If your gap is firing, it should work.

It should work with DC but I would recommend using AC. I would also recommend getting an old type (NO-GFI) neon.

Iâ€™m thinking that the coil is badly out of tune. Here is a good website that has all the coil calculations:

Also at 10kv that gap probably could be a little bit wider. It would also be a good idea to use forced air cooling on that gap. Something as simple as a PC fan would work ok.

Dash_Riprock

Mon Apr 07 2008, 12:45AM

Registered Member #1431 Joined: Sun Apr 06 2008, 04:59PM
Location:
Posts: 6

Thanks for all the help from everyone, but still no luck.

I tried opening the gap up to varying widths and quenching it with a vacuum cleaner- still the same results. I can see a spark about 1mm long when I touch the sphere, and about 5mm long when I touch the secondary about half way up. I also used the design tool at

, which says that my primary is 10% too short, and teslamap, which says the design is good.

The circuit doesn't work at all without the rectifier. Current just passes right through the 3nF capacitor like it isn't even there, and the gap never fires.

And I actually did have an 80mm computer fan on there originally, but I took it off because I thought such little airflow wouldn't have any significant effect. I will probably put it back on or make an entirely new gap if I ever get this thing working in the first place.

Also, I dont think the secondary wire is the main problem, since I get about 50 ohms from top to bottom on it and according to that java program I should be getting just under that.

MOT_man

Mon Apr 07 2008, 01:59AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Thats the problem Dash - you have a solid state NST. It really isn't going to give much power at all - in fact if you were to get something you'd likely blow the FETs in the transformer. My recommendation is to look at other coilers and get ideas from them. If you can spare some money you might make a trip to the hardware store and buy some 3-4" PVC pipe, end caps, varathane and some magnet/motor wire.
I think you have to start somewhere - but your coil set up as you have it won't do much good. Your going to need some components. I'd gladly help you out if you need some advice. Just send me a PM...
I teach Fine Arts - and have been in various large scale Tesla Coil demos for schools as well... I turn myself into a sculpture of sorts.
So - let me know what I can do to help.

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