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RE: [TCML] Jacob's Ladder
No intentions of creating controversy....just my experience...
I've had good luck using 1/4" copper tubing for Jacob's ladder electrodes.
In my design I utilized 1.5" long ceramic tube insulators (the kind they used in houses way back when to insulate wires in the attic) to get through the wood. I crimped the end of the copper tubing to make it fit into the wire hole of a heavy duty connector and bent the tubing into an s shape to route it to the end of the NST. I connected these directly to the NST.
This made the electrodes pretty stiff. The 1/4" tubing actually seems to work very well. Bends to shape fairly easily, but requires enough force that it won't bend out of shape once its set.
I've never been able to get a Jacob's ladder to function with a cap across the electrodes. It just makes an evil buzz sound.
Sorry Scott, I have to disagree on the voltage vs. current thing. Yes, you can extend a lower voltage arc of considerable current out a larger distance than a higher voltage and lower current, but the lower the voltage, the harder it is to get the arc self started across the same distance as is possible with a higher voltage. Which is why we use level shifters (voltage multipliers) with microwave oven transformers. Getting the spark gap to self start across a reasonable spark gap space (with a MOT without the shifting) is quite difficult, and then getting it to quench is damn near impossible once its started.
A Gabriel electrode helps with getting the arc to self start (google it), but really I've found the 15/30 to be an absolute minimum to obtaining a reliable ladder, and a 12/60 is really optimum if you want something impressive, and you'll still need the Gabriel electrode to make it work reliably.
If there are safety concerns, get an acrylic (or polycarbonate or pyrex, ect) tube with an inside diameter larger than the span of the electrodes and long enough that the electrodes cannot be touched easily, and mount this over the electrodes. This actually adds an echo/amplification to the sound and adds to the cool factor.
Spirals are tricky, and the main thing to consider is that a Jacobs ladder works by continuously moving the arc into the super heated (and there for more conductive) air space directly above the current position of the arc, so the spiral need to be going up more so than out to keep this convection process in play. Good luck with the spiral thing. Its tricky.
Shannon Weinhold
"Our virtues and our failings are inseparable, like force and matter.
When they separate, man is no more."
~Nikola Tesla
-----Original Message-----
From: Gary Lau [mailto:glau1024@xxxxxxxxx]
Sent: Tuesday, February 01, 2011 8:08 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Jacob's Ladder
Capacitors are NOT typically used in a Jacobs Ladder. Putting a cap in parallel with the NST and electrodes will make for a much louder sound, and it may also result in a brighter arc. However, this circuit can easily result in the destruction of the NST if the cap value is remotely near the mains-resonant value, because the gap on a JL is by definition, wide open.
I have seen a very impressive display that creates VERY long arcs using a ballasted pole pig and a series-connected capacitor. I suspect that this would also result in over-voltage damage to an NST so I wouldn't recommend this either.
I would recommend against using copper tubing for the electrodes. You need the electrodes to be straight and rigid, and copper tubing is neither.
Instead, go to Home Depot and get some 3 ft 1/8" steel rods, in the hardware aisle.
For "special effects", I've found that common table salt applied to moistened electrodes results in the brightest colors - even more-so than strontium salts. And skewered baby carrots yield a surprisingly bright and colorful arc.
Regards, Gary Lau
MA, USA
On Tue, Feb 1, 2011 at 11:39 AM, David Steinberg <david.steinberg@xxxxxxxxxx
> wrote:
> I have a 9kv / 30mA NST, some ¼" copper tubing, 7 CDE 942 caps
> (0.15mfd 2,000 v) and high voltage wire left over from building my tesla coil.
>
>
>
> I'm looking to construct a good jacob's ladder. Here are my design
> parameters:
>
>
>
> 1. The voltage / current should be sub-lethal. That being said, I
> think the 9kv transformer may not be powerful enough. I would
> consider building a voltage multiplier, etc., if that would help. Or
> switching to a
> 15 kv NST.
>
> 2. I'd like to use my left-overs, but I don't mind buying a few new
> things;
>
> 3. A simple coat-hanger V-design is out of the question. It must be
> interesting - perhaps a spiral, perhaps something different and
> interesting;
>
>
>
> I am looking for any and all ideas and / or designs. Should I go ac or dc?
> Is there a simple way to boast the power of the 9kv transformer, or
> should I go with something else? Anyone have a great and novel
> design?
>
>
>
> Thanks,
>
>
>
> David
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
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