opened pulse cap

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: opened pulse cap
From: Tesla List <tesla-at-stic-dot-net>
Date: Fri, 20 Mar 1998 22:53:13 -0600
Approved: tesla-at-stic-dot-net

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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Friday, March 20, 1998 6:23 AM
To:  Tesla List
Subject:  Re: FW: opened pulse cap

Tesla List wrote:
> 
> ----------
> From:  Homer Lea [SMTP:HomerLea-at-aol-dot-com]
> Sent:  Thursday, March 19, 1998 1:06 AM
> To:  tesla-at-pupman-dot-com
> Subject:  opened pulse cap
> 
> >I finally got one of my 60 kv 1,8 uf caps open. It is 12 sections each about
> 1 1/2 x 10 x 26 inches (not measured), all wired in parallel so  .15 uf per
> section.
> 
> I just unwound the first couple layers. The cap is made of strips of foil
> spaced apart with a second layer spaced alternately to give the effect of
> several caps in series. This double layered arrangement is then rolled up in a
> flattened coil. I will try to illustrate
> con__________        ___________         ___________         ____________
>                _____________      ____________      ____________
> _________con
> 
> Only the end two strips have an electrical connection (marked "con"). The ends
> are soldered with some kind of aluminum solder to tinned copper strips. Does
> anyone know how to connect the end foil back after rerolling part of the
> capacitor. Not only is it covered with oil but aluminum is hard to solder.
> Would some kind of compression connection be good enough? More news as I
> progress.
> 
> jim heagy

Jim,

Very interesting post, Jim! I have a similar cap that is 54 uF at 15 kV
that I tore apart (to the module level) after it catastophically failed
a while back. It had 28 identical flattenned modules all connected in
parallel. I suspect my cap may have been used more for Power Factor
Correction than for pulse duty. From the outside, these modules look
like single rolls, and the cap's construction seemed to violate the
"rule of thumb" about having many caps in series to obtain voltage
standoff capability. Your autopsy shows how this might be done!

On my cap, the conductive strips appeared to be tin or tinned copper,
and were also heavily soldered to the aluminum endfoil. Don't know if
the solder formulation is special (i.e., low melting indium alloy?). The
dielectric was a combination of polypropylene and kraft paper. I was
going to unwind one of these modules when I got a bit of time - I'll
definately do so now...

-- Bert --