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Re: Re. HDPE found: check my capacitor, please

At 16:01 20/10/98 -0600, you wrote:
>Lampblack carbon IS a pigment commonly used in paints and it is quite
>conductive, although the dielectric strength you listed below appears
>quite good.

I'll try to check, is it conductive or not.


>>Paper is 0.05 mm (40g/m2) kraft paper vaxed only on one side.
>
>"Vaxed" = Waxed?  The paper should be unwaxed, to be as absorbant as
>possible.

I called the paper company: nowadays they don'y wax (sorry about that vax)
anymore it. They just "mechanically" make one side shining.

>
>I don't know if you've thought this far ahead, but I found that when
>using extended foil construction, if there's more that one layer of poly
>and/or paper between plates, they're going to shift on the short axis as
>you roll, and since the foil extends on both sides of the poly, you can't
>see it, get at it, or do anything about it.  I've found no way to assemble
>this with more than one layer, and even then, I had to tape the foil to
>the plates to keep it aligned.  Do let me know if you have a way, as I'm
>struggling with this now.

I'm struggling too... Some ideas I got:

- I roll the foils around a 25 mm PP pipe were I have cut a long hole to
  insert the foil's edge and keep it there. Same idea that cash machines
  use to roll their printed paper bills.

This works great (tested yesterday): you don't need to cap the PP pipe (so
you don't enclose air in it). With the cut it the PP pipe you can really
roll thight that sheet pack: it won't slip!

- Have the rest of your family standing on the sheet pack laying on the floor
while you roll it. Still "untested".

>
>If your "sheets 23 cm wide" refers to the foil plate dimention that
>overlaps with the opposite plate, I calculate the capacitance per roll
>to be .012uF.  I assume you have about 5cm poly margin on each side of
>the foil beyond the 23cm width.

23 cm is the PE width. Leaving 1.5" per side I could have a usable width
of maybe 15 cm for the plates.

BTW, cannot I leave just 2 cm (0.79") per side? That would make a 4 cm
distance for the corona to jump, through oil. How much voltage that
gap will stand?

>A).  Having learned my lesson about sealing the caps, if I were to repeat
>the design, I would have a tube containing oil exit the cap enclosures
>into a small bottle.  If the temperature or pressure of the cap rises,
>the oil will expand like fluid in a thermometer and visibly vent slowly
>into the overflow bottle as an early warning sign.  Unless you can
>guarantee that the position of the cap will never change, I'd not leave
>any air in the enclosure.

But why not to leave vacuum?

>Good luck,
>Gary Lau
>Waltham, MA USA
>


________________________________________________________________________

 Marco Denicolai                   Vista Communication Instruments, Inc.
 Hardware Development Manager      www.vistacom.fi   

 marco-at-vistacom.fi                 Kaisaniemenkatu 13 A
 fax:    +358-9-622-5610           SF-00100 HELSINKI
 phone:  +358-9-622-623-15         Finland

   Remember, Murphy was an optimist! I am not...
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