The manufacture of capacitors

To: tesla-at-pupman-dot-com
Subject: The manufacture of capacitors
From: Gary Weaver <gweaver-at-earthlink-dot-net>
Date: Mon, 09 Dec 1996 07:21:42 -0800
When I was in high school I worked part time for a company called Misners.  I 
am not sure the name is spelled correctly.  They manufactured capacitors, 
coils and transformers.

Today while going threw my stuff I came across this information about making 
capacitors.

It might be of interest to someone.

  [ Part 2: "Attached Text" ]

The manufacture of self healing paper capacitors.


Capacitors made from paper and mineral oil will self healing.  A spark threw the dielectric will be healed while an arc may permanently damage the capacitor.

Material                  Dielectric constant        Puncture voltage per .001 inch

Paper                            3.0                                    200

Mineral oil                      2.7                                    200

Polyethylene                  2.3                                    450

PVC                              2.95                                   725



C=(0.224KA/d) (n-1)

C=capacitance in piecofarads

K= dielectric constant

A= area of one plate is square inches

d= seperation between plates in inches

n= number of plates

When calculating C use the lowest dielectric constant of all the materials used in a paper capacitor.

When calculating A use only the over laping surface area of the 2 metal plates.


plate----------------------------- xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
paper--------------------------------oooooooooooooooooooooooooooooooooooo
plate------------------------------------xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
paper--------------------------------oooooooooooooooooooooooooooooooooooo


Soak the paper first in mineral oil before rolling.

Put down the 1st dielectric material. 

Put on the 1st aluminum foil plate.

Put on the 2nd dielectric material.

Put on the 2nd aluminum foil plate


Roll up tight.  Aluminum on plate 1 will stick out on one end of the capacitor and the aluminum on plate 2 will stick out of the other end of the capacitor.



The machine used to make the capacitors is an X shape.  With a roll of aluminum foil at the top and bottom of the X.  And a roll of oil coated paper to the left and right of the X.  The capacitor being rolled is in the center of the X.  The 1st paper is started then the 1st plate then the 2nd paper then the 2nd plate.  The capacitor is rolled to the desired diameter to obtain the desired capacitance.  The plates are cut first and the paper is allowed to roll around a few turns before cutting.  Each roll of paper and aluminum foil has a tension device to hold tension on that roll and make the capacitor roll flat and smooth and tight.  All 4 rolls are rolled at the same time.

The rolled capacitors then goes to a work station where the wires are attached.  Two method of attaching wires are used.  1.  Unrap the end of the capacitor and lay a wire on each plate.  Then roll the ends down with the wire inside the unit.  A wire will be sticking out each end of the capacitor.  2.  A wire is punched threw the aluminum foil on the end of the capacitor and the foil is smashed down to make good contact and hold the wire in place.  This is done on both ends of the capacitor.

The capacitor then goes to a work station where it is placed in a case and labeled with the correct voltage rating a capacitance rating. 

Capacitor failure.  Method # 1 for attaching the wire fails before method # 2.  The wire tends to smash the dielectric material making it thinner at that point and it fails near the wire.  An extra layer if dielectric material can be placed near the wire to compensate for this problem.