Re: Coaxial Capacitor?

To: tesla-at-pupman-dot-com
Subject: Re: Coaxial Capacitor?
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Wed, 14 Oct 1998 16:56:15 -0600
Approved: terryf-at-verinet-dot-com

Hi Bob,

> Original Poster: Bob Wroblewski <bwroblewski-at-yahoo-dot-com> 
> 
> Hi All,
>   Has anyone considered using sections of RG-8/U coaxial cable as a
> homebrew HV capacitor? The insulating dilectric is solid polyethylene.
> The inner conductor is solid copper as is the braid shield.
>   The capacitance is 29pf per linear foot from an Aplha Wire catalog.
> Then 34 one foot long bundled sections equals a .001 uf cap.
>   Start with a bundle of 15 inch segments. Strip the outer braid an
> inch or so from one end. Connect all center conductors together,
> likewise connect all braid sections, rolled back an inch or so from
> the opposite end, together. Place in a 3 or 4 inch OD tube, (maybe oil
> fill?) and cap the ends (no pun intended) and extend a stud terminal
> to the conductors.
>   I'm sure if this worked well someone would have tried it by now and
> it would be spun off to others. So where's the flaw? Too costly per
> capacitance value? Area of conductors? Thickness of dilectric?
> Difficulty of assembly?
>  Just thinking, I've never tried it. Comments??

A year or two back I tried much the same trick with telecom cables 
where every second wire was extended beyond each end and parallel 
connected. I never used it on a TC but did test one to 15kVDC. I 
don't think the outer braid is the best conductor but neither was the 
PVC insulation in my cable the best dielectric for TC use. It was 
just a suggestion for someone who was looking for a cheap way to make 
a cap. The cable seems to pop up in surpluses from time to time.

Malcolm