Re: Spark gap not firing

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 2/2/01 8:45:06 PM Pacific Standard Time, tesla-at-pupman-dot-com 
writes:

<< I
 built a foil stack capacitor composed of five aluminum flashing plates that
 were 5" x 7"  sandwiched in between them was a rubberized adhesive coating
 which I do not know the exact K value for.  The rubber adhesive was four 
inches
 across and covered the length of the aluminum plate, giving a capacitor area 
of
 4" x 7". The rubber layers is about 1/64" of an inch across. >>
 
Michael,

I would say that your cap is shorting your NST out. You say that the aluminum
plates are 5" x 7" but your rubber adhesive strip is only 4" wide, if I'm 
under-
standing you correctly. The dielectric MUST must exceed all deminsions of
the conductor plates or the HV will easily arc around the egdes of the dielec-
tric or worse yet, the foil plates will lay on each other where they overlap 
the
dielectric and completely short out the transformer. You need at least a 1"
clearance of dielectric on all sides of the conductive plates, i.e.- 6" x 6" 
conduc-
tive plates need at least  8" x 8" dielectric plates between them.

Also, you will definitely need a dielectirc thicker than 1/64" for a Tesla 
service 
capacitor. And it will need to be oil-filled and vacuumed down or it will 
surely
fail. In my opinion, if you can afford it, you need to buy some of Terry's 
Pana- 
sonic .056 uFD MMC caps and build your cap from that. I think this would
save you a lot of headache in building your capacitor. I've successfully built
homemade caps that would hold a charge and give a visible spark discharge,  
but I have never successfully built one that was suitable for Tesla service. 
Some people have, but most them had skills and facilities  that are beyond 
the average hobbiest reach. And in the long run, it would probably be a lot 
cheaper for you to buy the MMCs than to buy the polyethylene sheets and 
alum. flashing and then it fail on you anyway :-(

My $.02 worth,
David Rieben