HDPE found: check my capacitor, please

To: tesla-at-pupman-dot-com
Subject: HDPE found: check my capacitor, please
From: Marco Denicolai <marco-at-vistacom.fi> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Tue, 20 Oct 1998 07:10:33 -0600
Approved: terryf-at-verinet-dot-com
After calling nearly 30 companies here in Finland, I eventually found and
bought 2 sheets of black HPDE, 0.8 mm thick, 1 x 2 meters. The company
ensured me that black color is just pigment, not coal or other conductive
stuff.

Declared properties are:

Dielectric constant:                    2.4
Dissipation factor (-at- ? Hz):            0.0005
Dielectric strength (? mm thickness):   80 kV/mm  (i.e. >2036 kV/mil)
Water absorption:                       <0.01%

Here the companies are divided between packing foil manufacturer (thickness
around 0.05 mm) and sheet manufacturer (thickness from 1 mm up). PE about
0.5 mm thick was really hard to find. PVC would be available about anywere.

The material is stiff but I have already tried and I can bend it. I have
decided to go with it and to build two capacitors as follows:

- rolled caps, sheets 23 cm wide, 2 m long
- extended foil design with alumininum food packing foil
- 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
- Aluminium extended edges are bended about the PP pipe and fixed with
  two hose clamps (Gary Lau design). Before to do this I cut away some
  parts of the aluminium to allow for oil to reach the capacitor inside
- One of the clamps is taken through a copper strip to the upper
  side of the capacitor, so I have both capacitor terminales on the same
  side of the capacitor
- Then two bolt terminals and two small valves.

Foils are arranged as:

- paper    INNER LAYER
- Al
- paper
- PE
- paper
- PE
- paper
- Al
- paper
- PE
- paper
- PE      OUTER LAYER

Paper is 0.05 mm (40g/m2) kraft paper vaxed only on one side.

Questions:

- is the sheet design OK?
- is the overall design OK?
- were do you get those small (2-3 mm) valves?
- how much voltage do you believe my capacitor will stand?
- after vacuum and oil fill, should I:

  A - fill the whole cap with oil
  B - leave some vacuum empty space
  C - let some air get in on the top of the oil (then I wouldn't need valves,
      just hose fits)?



________________________________________________________________________

 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...
________________________________________________________________________