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

To: tesla-at-pupman-dot-com
Subject: Re: Re. HDPE found: check my capacitor, please
From: Marco Denicolai <marco-at-vistacom.fi> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Thu, 22 Oct 1998 02:05:56 -0600
Approved: terryf-at-verinet-dot-com
At 17:25 21/10/98 -0600, you wrote:
>This won't work.  As you roll, the layers have to be allowed to slide on
>the long axis relative to each other, and this is unavoidable.  This is
>the reason I advocated cutting the foil plates into short sections - so
>they can be taped to the poly to establish a fixed margin, AND so that
>they can shift relative to the next foil segment as you roll.  Try it,
>you'll see.  Cap rolling would be a breeze if things didn't shift, this
>is what makes it so difficult.

The layers shift because of their thickness: the outer layer will require
more length than the inner one. Two more points:

1. I found 0.1 mm (4 mils) thick copper sheet, about 30 cm wide. That is
enough thick to stay together but not too thick like aluminium flashing.
I'll use that, as a single sheet (not many overlaying).

2. Family rolling could work like this: they stand, you roll maybe 20 cm
length,
the inner sheets will create a small bend, the family steps out of the sheets,
the bend relaxes and the sheets shift a little in the direction of their
length. Then again and again...
When you roll, helpers keep the sheets stright by standing on them. When
the helpers step away, you keep the sheets straigth by keeping the rolled
cap together.
It is still a lot of a work and you must be very exact.

>With extended foil construction, you only get 1X the margin for arcover
>distance, since the adjascent plate is extending over the poly edge.
>For a single unit capacitor, even a 1.5" margin is "marginal" (sorry).

You are right.

>If you do have only a 15cm overlap, then I calculate your capacitance
>will only be .0072 uF.  Is that what you're shooting for?  This is not an
>efficient utilization of your two 1M x 2M sheets, you'll have enough for
>two such caps.

You may think that this is stupid, but I am NOT looking for any particular
value(!). I am not seeking for resonant charging and I have also no idea
of what tank supply or even TC will use the caps I build.

I just want to have some "spare" caps more than my Maxwell caps to test new
TCs.

With my MOT supply I can charge also big caps, so too big capacitor is not a
problem. I am satisfied if I get a value between 0.01 and 0.002 uF, standing
20 kV DC, with two capacitors in series.

>No homemade enclosure short of a hermetically sealed glass-to-metal tube
>will maintain a vacuum over any significant period of time.  Your vacuum
>will slowly leak and you'd have air in your cap.
>
>Gary Lau
>Waltham, MA USA
>

Ahaa! Good to know: you know, these are my first rolled home-made caps.



________________________________________________________________________

 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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