[Prev][Next][Index][Thread]

cap specs or non-specs

Since 80% of email I've received from this group has been about 
capacitor specifications, I thought I'd weigh in on the discussion- 
even though in my own setup- a solid-state driver: the only resonant 
caps are in the oscillator circuit (a mylar 4700pf unit, and not 
really resonating: a relaxation osc) and the parasitic series resonant 
C from the coil to ground.

What I was getting at in my previous post is that it appears that 
there really is no specification at all in regard to these commercial 
caps that are rated to work with an AC transformer of X volts-rms.

Although the manufacture specifies that the cap will work with X 
volts, it really doesn't mean anything since, as I showed, and others 
confirmed, under some conditions the real voltage across the cap can 
be many times the rms transformer voltage.  (and confirmed again by 
the real world explosion of a very expensive cap)

I imagine that the situation results from a defense contractor selling 
to hobbytists.  In my experience in the semiconductor industry, in 
most cases the cost of testing and characterization of a mil device 
was many times the actual value of a similar commercial device. 

To many of you I imagine I am just stating the obvious; but to a 
person inexperienced in the world of component vapor specs, maybe you 
might save several hundred dollars that you could pay toward rent- or 
some other trivial expenditure.   :)  :)

I have worked as both a product engineer and a test engineer, so I am 
proposing that this group form its own specification for caps.  This 
can't be that difficult, and might extend the state-of-the-art.  Who 
knows, the next "black budget" gov. project might reference telsa 
group cap specs for some exotic cap application.

Finally, I am wondering about home built caps.  Tesla used bottles 
filled with salt water (no- not the cheapo seamed bottles of today, 
but real blown ones made out of decent quality glass- would probably 
be impossible to obtain except by custom manuf. by some glass blower) 
Using modern materials, maybe I am reinventing the wheel again, but 
what about polypropylene film caps using dieletric sandwitched between 
some thin brass or other metal and compression adjusted like in the 
small trimmer caps. It seems like an oil impregnated version of this 
would be ideal and cheap for amateur to build.  Poly sheeting is avail 
in many thicknesses from hardware stores.

Best Regards. Rob.