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Re: capacitor building info
---------- Forwarded message ----------
Date: Thu, 2 Oct 1997 11:15:14 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: tesla-at-pupman-dot-com
Subject: Re: capacitor building info
Great post Gwyn....
> From: Gwyn Zucca <gwyn-at-tcbod.demon.co.uk>
> To: tesla-at-pupman-dot-com
> Subject: capacitor building info
>
> Hello All,
>
>
> Following the recent exchanges about the use of paper in home made pulse
> capacitors, I have been speaking with one of the people at a company
> that specialises in high voltage, high energy capacitors.
>
> The guy seemed quite happy to talk to me about the way they construct
> there caps. He does not advise the use of paper in home made caps due to
> the difficulty in removing moisture in the paper, however he did give me
> some tips on the does and donts.
I would say hear hear myself. The thought of paper slowly turning to
carbon inside capacitors makes my stomach go into knots.
> He says obviously that everything should be as clean as possible. >
> Use the thinnest dielectric that is possible, they use polypropylene in
> the range 10 - 18 microns depending on application.
>
> Use multiple layers of the dielectric material here again they typically
> use 2 - 4 layers.
I am using 8 layers of 0.125mm polyethylene in the caps I am building
for the display coil. I still haven't figured out where to get rolled
polyprop here :(
> Limit the electrical stresses, by using many series modules of high
> capacity to get the appropriate value, for a cap having an AC rating of
> 15Kv, he advises 10 - 12 series units, he says that they would never
> exceed 1500 volt per unit in there professionally built capacitors.
That's an interesting one. Based on experience plus some reading on
pulse caps in HPE, I am looking at around 6kV peak across 1mm of
polyethylene. That equates to 230V/mil which seems lower than HPE
suggests some of the more rugged commercial caps use. I could be
tempted to go to 4kVpk and build four caps with about half the
dielectric thickness I was planning to use.
> Using 4 layers of a good quality polypropylene film in oil he says 10
> volts AC per micron of dielectric would be fair.
>
> They use foil of 5 microns thickness, here again the home made caps have
> to compromise, but try to keep the foil to less that 20 microns
> (barbecue cooking foil typically fails in this area ).
I am making extended foil jobs with ordinary old cooking type foil
(easy and cheap to obtain).
> All connections and bushings should be of a heavy duty construction,
> best
> to over engineer it, than be of an inadequate design.
>
> I plan to do some design and experiments in the near future using 6
> layers of 4 - 6 layers of 25 micron polypropylene film, which can be
> obtained from companies who specialise in retail packaging. The caps
> will probably have 12 modules in series, the whole being in oil.
>
>
> I would like to hear yours views on this.
>
>
> See ya...
>
>
> Gwyn
Again, thankyou for the information. My plans are already modified.
Regards,
Malcolm