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Re: Capacitors

Tesla List wrote:
> 
> >From julian-at-kbss.bt.co.ukFri Sep  6 22:00:49 1996
> Date: Fri, 6 Sep 96 11:38:52 BST
> From: Julian Green <julian-at-kbss.bt.co.uk>
> To: tesla-at-pupman-dot-com
> Subject: Capacitors
> 
> >The color of the spark always tells me a lot about a persons capacitor.
> > purple or purple-violet tells me the fellow is a novice and his caps are
> >at the very bottom of their performance curve.  Brilliant pretty blue
> >sparks are better but indicate high loss in the tank capacitor is still
> >taking place.  Rich blue-white sparks indicate only satisfactory
> >operation.  Snow white arc channels only fringed in brilliant blue
> >indicate top performance operation and snyergistic tank operation and
> >energy transfer.  With enough power input, to over come losses,  Mylar
> >and mica can give quite impressive sparks.  Both will heat rapidly and
> >only the Micas stand much chance of survival if long runs are the norm.
> 
> Thank you Richard for this posting, you explain a symptom that I am getting,
> namely the purple-violet sparks of the novice.
> 
> I must admit I thought that I had built a good cap having made it from foil,
> poly sheet and oil, using the extended foil ends to form the terminals.  I
> understand that the advantage of the extend foil ends allows terminal
> connection down one side of the cap plate thus keeping self inductance low.
> 
> My question is how do you make a good cap?  Or is the bad performance due
> to some other factor?   How much does conductor size of the primary tank
> circuit make a difference?   Size of toroid (14" on a 7" coil), operating
> frequency (220KhZ).  What I do know is that the sparks are not white.
> 
> My plan is to make as many mistakes on my current coil in order to learn
> the most from the experiance.   Work has just started on a 10" coil which
> I hope to fire at 10KVA.
> 
> Any comments most welcome.
> 
> Julian Green


Julian,  It is very difficult to make a true polyethylene capacitor which 
is less than fantastic.  End foil won't help you.  It sound as if 
something else is reducing the performance.  Perhaps too much cap and not 
enough transformer.  To big a toroid for too low an input power will also 
do it.  Does your cap glow with corona when it is run?  Put two or three 
in series until no corona exists.

Richard Hull, TCBOR