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Re: Rolled PE design question

Chris,

The capacitance will be almost exactly twice as much rolled up as
unrolled - allwoing for some slippage of the plates when you roll it. If
you think about it you are simply doubling the area of dielectric which
it between the cap plates and thus doubing the capacitance. Just like in
a multilayer cap - each plate will then have a dielectric then the other
plate on *both* sides as opposed to one.

You talk of using an "insulator" - this will always form some kind of
dieletric when rolled up - it's simply that PE has good strength and is
much cheaper than, let's say, teflon or polyester in the thickness you
will require to prevent breakdown.

The tightness of rolling isn't really an issue (unless the thing is
pretty loose, in which case you're asking for corona and simply reducing
capacitance by having extra space in addition to the dielectric). In any
rolled cap properly made (and when vacuumed) there should be very little
extraneous space anyway).

Stick with the PE, you'll save money that way! I have spent about £150
for making up a two-layer 0.06uF cap, although I'm gonna try with half
that to begin with, as resonant charging is not strictly neccessary.

Good luck

Alex



Tesla List wrote:

> Original Poster: Chris Tominkson <internetinbox-at-yahoo-dot-com>
>
> But do you calculate this extra capacitance in? And
> also that would mean that the tighter the roll, the
> more capacitance you would get, right. Well, anyways I
> was just trying tosave some PE so I could make more
> caps later...
>
> Chris.
>
> --- Tesla List <tesla-at-pupman-dot-com> wrote:
> > Original Poster: Hollmike-at-aol-dot-com
> >
> > In a message dated 3/29/99 3:12:09 AM Mountain
> > Standard Time, tesla-at-pupman-dot-com
> > writes:
> >
> > >
> > >  So my question is, could you replace the extra PE
> > layer
> > >  on the bottom (could be on top) with an
> insulater?
> > >
> > >  Thanks in advance, Chris.
> > >
> > Chris,
> >     The "extra" layer of PE is needed.   If you
> think
> > about it, the
> > capacitance will double in a rolled cap vs. a flat
> > plate cap of the same area
> > (with two plates) due to the backsides of the plates
> > acting like a third plate
> > once rolled.   Would it not make sense to use the PE
> > rather than some other
> > insulating(dielectric) material?
> > Mike
> >
> >
>
> ===
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