David Steinberg wrote:
Thank you all for your suggestions. I'm considering the glass enclosure with argon gas. As I've never worked with glass enclosures or argon before, I have a couple of questions: 1. What length of arc should I expect?
The breakdown and reignition voltage of argon is considerably lower than air, and an argon arc will typically be ~5X the length of an arc in air under identical conditions.
2. Does anyone have a basic design for this?
Scale up the gap/design of a regular air Jacob's ladder for the desired voltage. Because of the lower breakdown and arc extinction voltages, you should be able to drive a very wicked ladder from one or two ballasted MOT's, and the argon will make the arc easier to (re)start at the bottom of the ladder. The sides of the cylinder (or box) must be at least a 2-3 inches away from the arc to prevent the heat of the arc from damaging or fracturing the sides of the container.
3. Do I need to "de-gas" the glass before filling with argon?
This will not be necessary, since you'll be running it at atmospheric pressure. Argon is about 38% denser than air, so you can "fill" your glass container by injecting argon from the bottom, displacing the lighter air above through the open top. Completely enclosing the top can be done but is not necessary since the cost of the gas is relatively low. Leaving the top open also simplifies convective flow and shedding heat from the arc. You can continuously inject a small flow of argon at the base of the container to keep it full of gas while running the ladder.
4. Where do I get argon?
Fortunately, argon is relatively plentiful (about 1% of the atmosphere). It's primarily used for inert gas (TIG) welding or as an inert gas blanket to prevent oxidation or combustion. You can buy or rent a cylinder of argon (or various mixtures of argon and other gases that are mostly argon) at welding supply houses. These mixes will work almost as well as pure argon for your application and may be less expensive than pure gas. You can occasionally get smaller "lecture bottles" of chemical grade gas or small CO2-cartridge-like containers for using as an inert gas blanket to keep wine from oxidizing, but these are significantly more expensive per liter of gas. Also, check eBay or local chemical supply houses.
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Thanks, David -----Original Message----- From: jimlux [mailto:jimlux@xxxxxxxxxxxxx] Sent: February-01-11 2:37 PM To: Tesla Coil Mailing List Subject: Re: [TCML] Jacob's Ladder On 2/1/11 9:35 AM, Scott Bogard wrote:Hi David, It is the current that nearly solely determines the range an arc can be stretched, so I imagine there will be no improvement at all upgrading to a 15kV NST. You can add another 9kV in parallel, and it will make your arc stretch much longer, but also puts you deeper into "lethal" territory (most likely not, but there is always a chance.) DO NOT USE DC!!!!! If you touch a wire it will latch onto you and you will die an agonizing death. Ac will let go in one 60th of a second and muscle contractions will pull you off of the wire, substantially safer.Not entirely accurate, but, in general, you shouldn't be touching either. If you want to do something cool and new, I would suggestbuilding a glass enclosure and filling it with with an argon gas/air mixture, with the right concentrations you can make cool colors, get a much longer spark, but still have it keep it's Jacob's ladder characteristics. Not to mention a glass tube will support a helix shaped ladder quite nicely. Food for thought.You can do spirals quite nicely in air as long as you have something to hold the top of the ladder still. For fun, put things in between the electrodes (but not touching) that have been dipped in suitable salts (strontium and barium compounds are nice). A tennis ball works nicely, although the smell of burning wool (the fuzz) is kind of disgusting. A cork works too. The sparks will go around the surface, and be strongly colored by the salts. _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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