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Re: [TCML] Spark GAP



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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