Re: Capacitor plastic thickness

To: tesla <tesla-at-grendel.objinc-dot-com>
Subject: Re: Capacitor plastic thickness
From: Richard Hull <whitlock-dot-com!RICHARDH-at-uucp-1.csn-dot-net>
Date: Thu, 04 Apr 96 15:14:00 PST
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Ed,

The pros start by avoiding polypropelene dielectrics much thicker than 1 
mil!  .5mil is preferred (this stuff tears if you look at it wrong).  This 
thickness is the point where a dielectric exhibits its greatest strength 
often in excess of 10kv/mil!  thicker sections of the same dielectric have 
the strengths plunge to ~500v/mil.  Next they use 1/4 mil foil from a long 
roll.  The rolls of dieletric and foil are threaded onto a machine which 
high speed rolls hundreds of feet per minute into an "extended foil" design 
cap.  With stuff this thin and tightly wound, virually zero air is present 
in the cap. The foil ends are then crushed to a mass of aluminum on each end 
of the finished cap.  These caps are then aluminum soldered/welded together 
in a group of series connected caps to yeild the desired capacitance. 
 Finally this is assembled in a case which is filled with silicon oil (in 
the better caps) and a vacuum is pulled to remove all traces of trapped air. 


Please note that the best caps for Tesla work are pure polypropelene film 
and aluminum.  They are filled with silicon oil (must be specified) and 
should always be in a plastic case with end terminals.  Caps placed in 
welded steel cases with beautiful insulators are pretty, but exhibit about 
100% more internal inductance and cost a fortune extra.