Re: failed cap

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

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net> 

Hi Gerry,

I have, using eight 0.004" polyethylene sheets between plates in a flat 
plate cap to form a module that was then connected in series with 1-3 
identical modules. The cap is still going strong after 7 years of use (and 
abuse). The tough part is getting the air out from between all of the sheets.

All commercial film capacitor vendors use the multiple layer technique with 
two layers of dielectric because it works so well.

Best regards,

-- Bert --
-- 
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Tesla list wrote:

>Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net>
>Has anyone tried to use two or three layers of thinner PE dialectric between
>plates to allow statistics (of having the defects of those multilayer sheets
>line up at a common point) to improve the reliability of the home made cap.
>Gerry R
>Ft Collins, CO
>  > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
>  >
>  >
>  > Any home brew caps using a relatively thick dielectric (64 mil) is subject
>  > to this type of failure.  You had some small voids in the dielectric.
>  > Inside these voids the dielectric constant is different from the
>surrounding
>  > material.  The result is corona inside the small void.  Corona produces
>heat
>  > and eventual failure occurs.  Some of these voids are so small they almost
>  > can not be seen with the human eye.  As the corona forms immediately,
>  > breakdown begins.  It's a slow process but eventually the void produces
>  > dielectric failure as you have experienced.
>  >
>  > Professional manufacturers always use 0.5 (1/2) mil thick dielectric
>  > material to avoid this problem.  This dielectric material is so thin it
>can
>  > only be handled by expensive winding machines and can not be touched by
>  > human hands.  The entire surface area of this dielectric material is
>checked
>  > for voids prior to acceptance by the cap mfgr.
>  >
>  > I toured Maxwell Capacitors years ago and they use a "clean room" for all
>  > their special energy discharge cap winding processes.  Some of their other
>  > processes such as soldering extended endfoils together were equally
>  > interesting.
>  >
>  > Stick with the MMC caps and a 2.5:1 ratio (DC to AC) and you will have
>  > virtually no trouble in the future.
>  >
>  > Dr. Resonance
>  >
>  > Resonance Research Corporation
>  > E11870 Shadylane Rd.
>  > Baraboo   WI   53913
>  >  >
>  >  > Hi.
>  >  >     i built a cap with 1.6 mm or 64 mil thick PE dielectric and put the
>  >  > whole thing in canola oil. It worked great for a while but while i had
>  > just
>  >  > the cap across the nst ,,, with no tesla coil connected.. to test my
>new
>  >  > mulitgap sparkgap... the PE between 2 of the plates broke down and now
>it
>  >  > blows bubbles and hisses and only produces a spark in the gap if the
>gap
>  > is
>  >  > 1 mm or 30 mil . Its pretty much had it and must be breaking down at 1
>or
>  > 2
>  >  > thousand volts..IS it more stressfull on a cap with no tesla coil
>  > connected
>  >  > and is it suprising my cap did not last in my config. The plates are
>1.75"
>  >  > clearance from each end and 1" along the sides. !6 sheets of makes each
>  > layer
>  >  >
>  >  > Phil
>  >
>  >
>
>.