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Re: Multi-Rolled Cap

Subject:  Re: Multi-Rolled Cap
  Date:   Sun, 18 May 1997 13:07:55 -0500
  From:   "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>
 
> 
> Greetings All,
> 
> I have been following the posts on
> building caps and I understand the
> advantages of putting caps in series.
> 
> Let me represent 4 caps in series as
> 
> -----||---||---||---||-----
> 
> This is equivalent to:
> 
> ----|||||------
> 
> That is why not make a sandwich of 5 plates
> of Al foil seperated by polythene sheets.
> No connections are made to the 3 inner plates.
> This would be very dificult in a rolled cap,
> because of the number of layers. But easier
> in a flat cap. The layers would need to
> be staggered. Again showing only the foil:
> 
> ----------------------------
>      ------------------------
>       ------------------------
>        ------------------------
>         ------------------------------ 
>        ------------------------
>       ------------------------
>      ------------------------
> ----------------------------
>      ------------------------
>       ------------------------
>        ------------------------
>         ------------------------------ 
>        ------------------------
>       ------------------------
>      ------------------------
> ----------------------------
> 
> I think that this would save some material.
> and interconnections. And that it might be possible
> to prevent corona forming inside the cap,
> by reducing the electric field - oil will
> still be needed at the edges - where it can
> penetrate most easily.
> 
> The inbetween foil layers are used to even out
> electric field - no current is drawn from them
> so I think cooking foil would do.
> 
> This is just a thought - I haven't tried building
> caps yet - wait for the comments of the "old wise
> ones" before trying it yourselves.
> 
> Have fun,
> 
> Alan Sharp.

Alan,

I think your idea is a good one and deserves to be tried.  Employing 
the foil as equipotential layers ought to get more space efficiency out
of 
the amount of plastic sheet dielectric used. 

I've seen a couple of very negative replies about your idea and I 
still think it is worth trying.  Although you might have to derate 
the voltage per sheet of dielectric, the net result may still be more 
compact than these other homemade caps.  As also pointed out by 
others, this design will be less forgiving of impurities or blemishes 
in your plastic.  Only virgin cap grade poly should be used I guess.

Please keep us informed if you decide to 'do the experiment'.

rwstephens