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To short secondary coil, can I use it for anything?

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Estragon

Sat Sept 13 2008, 07:37PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Aha, so just solder them against each other. Don't twist them or anything?

Fraggle

Sat Sept 13 2008, 08:38PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

When I snapped my secondary I didn`t make any specific electrical connection, just laid the stripped wires together and varnished over the top. The performance seems unaffected even though the thing is an open circuit to DC.

uzzors2k

Sun Sept 14 2008, 01:50PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Estragon wrote ...

Aha, so just solder them against each other. Don't twist them or anything?

Nope. Just solder.

Relying on the secondary voltage to jump the gap might work for SGTCs or fixed frequency SSTCs, but not for self tuning SSTCs. The inductance of the secondary would change to much for tuning to be possible.

Antonio

Sun Sept 14 2008, 11:31PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

My all-purpose secondary coil has five solder joints, as it was made with wire taken from discarded relays. No problem at all. Scrap the enamel from a few mm, solder, continue the winding with the solder joint placing one wire over the other, to not leave a gap in the winding, and after completing the winding apply several layers of varnish over everything, with some excess over the joints.

Estragon

Mon Sept 15 2008, 02:08PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Eeew. Today I got a lot of new wire, but it appear to be a bit thiker. I guess this is 0.30mm and the original wire is 0.25mm. Not that big a difference, but how you think that would work for a normal SGTC, would it be messed up or can I continiue with the thiker wire?
Maybe I should make another secondary with the new wire, but I don't know if it is enough for a complete coil.

Seoul_lasers

Tue Sept 16 2008, 12:33AM

Registered Member #1630 Joined: Sat Aug 09 2008, 11:36AM
Location: Seoul Korea
Posts: 115

Yes, I think it is just fine.

teslacoolguy

Tue Sept 16 2008, 02:56AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
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Posts: 792

Maybe you should use the larger wire for the bottom of the coil since there is more current than voltage down there.

Myke

Tue Sept 16 2008, 03:22AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

How is there more current than voltage near the bottom of the coil? I would say that the highest voltage and current would appear where there is more coupling right? I don't know though. Another chance to learn :P.

Dr. Dark Current

Tue Sept 16 2008, 06:04AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Myke wrote ...

How is there more current than voltage near the bottom of the coil? I would say that the highest voltage and current would appear where there is more coupling right? I don't know though. Another chance to learn :P.

It is commonly known occurence that the bottom of the secondary heats considerably more.

I may not be right here but maybe its probably because the secondary wire lenghts are often near quarter wave wavelength of the drive frequency, which would ideally mean that there is only current at the bottom and only voltage at the top?

Steve Conner

Tue Sept 16 2008, 10:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes Dr. kV that explanation is correct. Unless you use a huge topload, in which case the current at the top of the secondary is almost as big as it is at the bottom. (And the resonant frequency is considerably less than the quarter-wave frequency.)

But remember that the quarter-wave resonance of a Tesla coil is different to the frequency at which the length of wire in it forms a quarter wavelength. When the wire is coiled up, the electric and magnetic coupling between turns shifts all of the resonant frequencies. The math needed to prove this is scary, though.

I actually have the top of my DRSSTC secondary wound with 0.315mm magnet wire, and the bottom 2 inches with 7/0.2 stranded wire, then I wrapped the whole lot in black electrical tape to hide the mess. It ended up that way because flashovers burnt the bottom 2" beyond repair, and I thought the thicker wire would stop them, because it would have fewer turns, so less induced voltage.

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