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Re: [TCML] Spark GAP



bunnykiller wrote:

Hey Robert...

wonderful idea but not the proper material... probably conductive to boot.... the disc is brittle and designed to wear away as it is used. Ergo, the material is not homogenious ( actually the grit is held together with an epoxy) and very prone to shattering in the wrong application.

When designing a rotory spark gap, you NEED a material that is either homogenious ( solid metal, etc. :) ) or a cross fiber patterned laminated material ( G-10 is a popular choice). When you put several ounces of tungsten into the periphery of a rotating disc and spin it up to or past 1800 rpm, the electrodes can produce in excess of 5+ G's with no problem. Can you say bullet? ;) Another consideration to ponder is the amount of heat that can be transfered to the disc via the electrodes. Since heat can be a problem, this leaves out using plastics that can become soft at less than 400 degrees F ( which is most of them).

There are about 3 general designs for rotory gaps
1. 1/4 - 1/2" thick, 8 - 10+" dia. disc with electrodes approximately 1/2- 3/4" from edge ( G-10 being the popular choice) Pole piggie usage. 2. propeller gap, basically an insulative hub holding a "lengthy" ( 8" or so) piece of tungsten rod ( hub being UHMW PE) normally used in NST applications. 3. a work of art, the gap used in the China Olymics Tesla coil ( probably cost as much as a small pick up truck).

When designing for Tesla coils, there are a few things to remember
Primary voltages can be from 5KV to 30 KV, insulation is a prime factor ( especially after 25KV) Secondary voltages can range from 50ish thousand volts to 1.5+ million volts ( not much can insulate against that... think lightning) Spark gaps create plazma... I dont know of much that can resist the errosive effects it can produce... but tungsten does seem to hold its ground to a degree...

Browse the active websites, see what is normally used... its been tested and most likely works most of the time. There are exotic materials out there that can be substituted, but the cost factor is the determining point of implementation.

Alot of great ideas come from the "What if" attitude... it gets people thinking and wondering....

Scot D



Robert Davies wrote:

WOW!!!

http://tesladownunder.com/

I was at Lowes yesterday and I was looking at a 7 1/2 angle grinder disc, it has a threaded center and can handle high rpm. Has anyone used this type of material for a spark gap?

http://www.lowes.com/lowes/lkn?action=productDetail&productId=22836-70-DW4999&lpage=none <http://www.lowes.com/lowes/lkn?action=productDetail&productId=22836-70-DW4999&lpage=none>


Rob
KI4HXT
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Thanks Scot, this is exactly the information I was looking for. I'm leaning heavy toward the propeller gap, I have a large supply of various sized tungsten electrodes for my TIG welder 1/8,3/32 etc. plus it looks like a simple no fuss design and since I will be using a 15/60 or 15/30 NST it would be the best choice.
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