Idea for Capacitor

Subject:  Idea for Capacitor
  Date:   Tue, 10 Jun 1997 19:13:11 -0400
  From:  "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To:  <tesla-at-pupman-dot-com>

Fellow Coilers,

Fr. Tom here again with some more food for thought.

As I mentioned in one of my previous posts, I am going to be away
from my usual residence (I live in a school building in Paterson, NJ)
for the summer. I *hope* to be able to get online at my summer
assignment (giving five one-week retreats to groups of sisters), but
I cannot be sure about getting online. 

So, I want to pass along an idea I have been working on, but will
definitely *not* be able to do any final work on until after the
summer. I am passing it on now in the hopes that someone else out
there who has the time will try the idea out and report back to the
rest of us.

We all know that the major failure mechanism in our Homemade High
Voltage Capacitors for Tesla Coil use is those stinking air bubbles
that get trapped between the plates. As you may remember from
previous posts, I have had good success with using paper between the
plates so as to actively wick oil in between the plates. In
multi-layer dielectrics I also use paper between the dielectric
layers, and not just between the plates and the dielectric.

I have noticed that one of the major frustrations for many coilers is
the long wait they have after building a capacitor as they wait for
the bubbles to subside. 

I think I may have a solution that will work for flat plate
capacitors at least. What we want to do is build a fairly regular
flat plate capacitor, but with three special features.

Feature One: The use of oil-soaked paper placed between all capacitor
surfaces, whether metal to dielectric, or dielectric to dielectric.
Pre-soaking of these pieces of paper may be just a slight bit on the
messy side, but will allow us to ensure an initial starting condition
that is already oil-rich exactly where we need the oil the most.

Paper pieces should be smooth, absorbent, clean paper. Kraft paper
used to wrap packages works well. Paper should be soaked for at least
an hour before use. Before soaking in oil, cut the paper so that it
is AT LEAST as large as the polyethelene sheets. A slight overhang
along all edges is actually useful. I would recommend 1/4" of
overhang on LARGE size plates, and at least 1/8" overhang on smaller
size plates.

Feature Two: Build up the flat plate capacitor on a COMPRESSION
FRAME! Imagine a flat plate capacitor sandwiched between two very
rigid non-conducting plates such as 3/8" plexiglass or 1/4"
fiberglass board. In a pinch you could use 3/8 or 1/2" plywood even,
although the thought makes me want to barf. I would envision using
something rigid which would NOT soak up oil.

Note: Don't make the compression plates too thin. Remember that they
are there to allow us to apply fairly decent pressures to the
capacitor. Skimping here can cause the material to crack. Oh yes, do
not put holes too close to the edge of the plexiglass or the pressure
make cause cracking from the holes to the edge. I planned to use a
metal washer of decent size anywhere a bolt head or nut was pushing
against the plexiglass. 

This frame would have long bolts holding the two frame pieces
together, with the capacitor sandwiched in between. I would envision
using bolts every inch or so along the WIDTH of the compression
frame. My own design plans call for me to use the bottom compression
frame as the building support for the actual capacitor. 

Feature Three: The inside face of *the Top* compression plate should
*NOT* be flat! To force the stinking air bubbles *OUTWARD* and away
from the center of the capacitor can only be accomplished if we have
MORE pressure along the center of the capacitor. 

We can accomplish this by making the center of *one* facing
compression plate thicker than the ends. An easy way to do this would
be to cut out about five pieces of poster board or thin vinyl or
WHATEVER for each compression plate. The thicker the capacitor, the
thicker this flexible material has to be. I suggest something that is
impervious to the oil, but in a pinch posterboard is OK. 

The largest should be about the same size (length and width) as a
sheet of dielectric. (By width I mean the shorter of the two

The next sheet should be about 20% smaller along the LARGEST
dimension of the capacitor, and the same width as the smallest
dimension of the capacitor. As each smaller piece of poster board is
cut, keep the width constant, and the length reducing by about an
additional 20% with each new sheet. Obviously you could also use
thinner sheets, more of them, and therefore make the size reduction
per sheet smaller, such as by 10%. The numbers used in this example
are just for illustration purposes. Once you understand the basics of
what we are proposing, modify as necessary!

Note: If the above technique is applied to BOTH compression plates
instead of just the top one, then the material can be thinner, as it
will be basically doubled by being made in two sets. (It will be more
work, but the end result will be slightly better, as forces will be
more evenly distributed.)

Before attaching the top compression plate, lay the cut strips down
on the top of the capacitor. They should all be the same width as the
width of the capacitor. The SMALLEST one goes down first. Center it.
Place the next larger strip centered over the first strip. The widths
should all be the same, and lined up with the width of the dielectric
sheets. Keep adding the larger pieces until all are centered and in

After the capacitor itself is built up, the compression frame top
would be put on and all the bolts tightened a little bit at a time. I
would begin by finger-tightening only and adjusting until  the frame
was levelled out with equal distances on each bolt being used. Then I
would use a wrench or nut driver to tighten each bolt in turn, by
just a quarter turn at a time. I would continue this until the whole
thing was level and extremely tight. Note that at this time most of
the oil will have been squeezed out. That is exactly what we want.
Because along with most of the oil, almost ALL of the stupid air
bubbles would have been compressed out.

Because of the extra pieces of flexible material, the pressure
applied at the center of the capacitor will be greatest. Thus, as you
tighten the assembly, air and oil are first driven away from the
center and outward. As compression continues the bubbles are forcibly
removed, but the absorbent paper will ensure that oil will still be
available between each sheet of dielectric.

The BEST thing to do with this assembly is to immerse it in oil. Note
that it will be instantly ready to be used. It should not require any
waiting, since all the air has been forcibly removed. 

By the way, if the final stages of tightening are done while the unit
is immersed in oil, then you will have an even better final product.
This is, however, just a tad messier. The capacitor can remain flat.
It does not need to be placed sideways. It can be mounted in ANY

Taking care of it would mean just swishing the oil around once in a
while to disperse surface bubbles. If you wanted, you could loosen
all the bolts, wait a minute or two, and then re-tighten them. This
would cause fresh oil to circulate and replace the old oil.

This capacitor would *NOT* need any form of vacuum to make it

Because of the compression frame, the capacitor would be robust
enough that it could be moved and handled fairly roughly. It is also
interesting to note that for transporting such a capacitor, you could
drain the free oil out and into another container. Once you got the
capacitor to its destination you would just pour the oil back in,
wait a minute or two, swish the tank to allow surface bubbles to
break free, and fire up your coil almost immediately!

I hope that someone out there builds a capacitor like this and gets
back to the rest of us on their experience with it.

Fr. Tom McGahee