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Re: Glass/poly and more...
From: David Sharpe[SMTP:sccr4us-at-erols-dot-com]
Reply To: sccr4us-at-erols-dot-com
Sent: Sunday, September 14, 1997 9:15 PM
To: Tesla List
Subject: Re: Glass/poly and more...
Tesla List wrote:
>
> From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
> Sent: Sunday, September 14, 1997 5:09 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Glass/poly and more...
>
> Hi all,
> I've been reading with interest the ongoing discussion about
> homemade caps, untimely deaths etc. Got a couple of things to say:
>
> (1) Motor oil is a no go. I have tried it and discharge or no inside
> the cap, the oil has polymerised and turned to sludge.
> (2) I have given a homemade poly/transformer oil flat plate cap a
> *real* thrashing now and it looks like lasting forever! Two things
> have contributed to this: it was left standing in oil for nearly a
> year prior to serious use (and during that time the bubbles have
> slowly seeped out of it). The second is that it is built in two
> sections of equal capacitance and is solely being run with the two
> sections in series. I took very much to heart what Richard Hull had
> to say about cap design and am completely confident of building the
> ones I am going to use in the commercial job and having them last the
> distance.
>
> Malcolm
Malcolm, ALL
I have four(4) 60mil PE capacitors under in oil in service on a 1kVA
magnifier (11kV non shunted 450VA xfmr, with resistive ballast). I have
had no failures or problems with the basic flat plate design. The caps
are under Exxon Voltrx N61 inhibited transformer oil.
The only difficulty I have run into is not allowing sufficient margin
around electrodes and the capacitor failing by arcing around the
dielectric material under oil. This occurred on a 500pf unit, used
as a HV EMI filter bypass cap in my 5kVA magnifier in the "early days".
If the cap arcs, the oil will discolor. I have also used mineral oil
(USP, as well as clear baby oil), with no problems.
Regards
DAVE SHARPE, TCBOR