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Re: Foil Caps (was Cap Pr (fwd)



---------- Forwarded message ----------
Date: Sun, 02 Mar 1997 07:29:30 -0800
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Foil Caps (was Cap Pr (fwd)

Tesla List wrote:
> 
> ---------- Forwarded message ----------
> Date: Sun, 02 Mar 1997 17:27:40 -1200
> From: Ken Smith <ksmith-at-ihug.co.nz>
> To: Tesla List <mod1-at-pupman-dot-com>
> Subject: RE: Foil Caps (was Cap Pr (fwd)
> 
> At 14:13 01/03/97 -0700, you wrote:
> 
> >
> >        If any are of a mind to "pop out to the supermarket" I strongly
> >        recommend "popping out" to a cash-and-carry type of wholesale
> >        grocery.  (See Yellow Pages, in the U.S.)
> >
> >        Such groceries have foil in  l o n g  rolls.   Many such
> >        also have foil in pre-cut 12" x 12" squares.  And the cost
> >        per unit length is apt to be much lower than in a supermarket.
> >
> >        And do get the heavy-grade (so-called broiler) foil.  The
> >        regular stuff is so flimsy that using it is like trying to
> >        whittle Jello.
> 
> Have done same, although we don't have the luxury of the big Cash and Carry
> places near here (say 4000 nm <g>) However I did find some respectable foil
> in 4.5m rolls (450mm wide) and used that to cludge some new caps together.
> 
> Now here is a problem.  Two plastic sheetings.  Both the same thickness
> (builders yard stuff).  One black one clear(ish) The clear is 3 times the
> cost of the black.  What is the difference ?
> 
> Can I use the black sheeting for a cap ?  If the answer is no, I have wasted
> a morning <Aggggh>
> 
> Ken
> 
> Ken Smith
> Auckland

Ken,

The clear sheeting is definately preferred, since it's "pure" low
density polyethylene/polythene (LDPE). White, black, or brown pigmented
material contains a colorant. These colorant "impurities" generally
degrade the dielectric performance of the LDPE by increasing the
dissipation factor and reducing the breakdown voltage. The latter would
be especially true if the black colorant was conductive carbon-black. 

For reliability, I'd recommend taking the material back for credit and
getting the clear material instead. Sorry 'bout that, but at least you
didn't build the cap out of the stuff yet! :^)

Safe cappin' to ya!

-- Bert H --