Re: Please help with capacitor

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

Original poster: Esondrmn-at-aol-dot-com 

In a message dated 1/6/04 10:24:56 PM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:

Dan,

I have made several rolled poly caps as well, many years ago when I first 
got into coiling.  You certainly can make rolled poly caps that will 
survive and work well in service.  If adequately designed, they take up a 
lot of room, require thick dielectric layers (or several in series) and 
don't produce many microfarads at our voltage level per cubic foot - if you 
know what I mean.  I started out with one dielectric layer of .0625".  Two 
of these worked well at 12 kv rms when used in series.  Both failed when 
used in parallel at 12 kv.  I rebuilt one with two layers of .065 poly and 
seems bullit proof but is low on capacitance.  My opinion is 4 layers of 
.020" poly or 3 layers of .030" poly is required to work at 12 kv.  I would 
question the reliability at 15 kv.

Ed Sonderman

>Original poster: dhmccauley-at-spacecatlighting-dot-com
>
>I might have to disagree.  Richard Hull was using rolled poly caps in many
>of his magnifier coils which I have seen in a few of his videos.
>He was using these with both 14.4kV and 34.5kV potential transformers.  I
>believe he used two of these caps in series for an equi-drive type
>system for use with his magnifiers.
>
>Dan
>
>
> > A home made cap used with a 15kV power supply must be made from at least 2
> > or 3 individual caps, in series.  A single
> > cap will fail due to corona at the edges of the foil.  I spend a huge
> > amount of effort on two attempts at rolled poly caps.  The first used a
> > single layer of 40 mil poly, and dies after a few minutes.  The 2nd
>attempt
> > was made with two units in series, each with a single layer of 40 mil
> > poly.  It too died after several minutes (see
> > http://www.laushaus-dot-com/tesla/rolledcap.htm).
> >
> > Assuming you are using 60 Hz power, your cap is mains-resonant with the
> > NST, and this is a bad thing.  In addition to being healthier for the cap,
> > I have found that a value of about 2X the mains-resonant value gives the
> > best performance with a static gap.
> >
> > Regards, Gary Lau
> > MA, USA