More Capacitor Ideas

Subject:  More Capacitor Ideas
  Date:   Thu, 12 Jun 1997 14:10:20 -0400
  From:   "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To:  <tesla-at-pupman-dot-com>
    CC:  "Tesla-2" <tesla-2-at-emachine-dot-com>

Fellow Coilers,

Fr. Tom here again.

As regards my post about using a compression plate for eliminating
bubbles from capacitors:

Malcolm mentioned that plexiglass is too easily bent to allow a lot
of compression. My solution would be to get something like a sheet of
1/4 inch fiberglass, and to use lengths of aluminum angle bar across
the width. Thus every set of holes along the side would have an angle
bar connecting across the width. We would need these on both the top
and the bottom compression plates. Angle bar is extruded aluminum (or
iron or whatever) in the shape of the letter "L". It is extremely
strong for its weight. It is available at building supply stores. 

In a pinch you could use almost ANY material for the compression
plates then, as the actual FORCE is being supplied by the angle bars,
and the compression plates just sort of hold everything together and
average out the forces. Material should be flat on the side that is
up against the capacitor. Just make sure the material is at least 1/4
inch thick and won't crack under the pressure. You would probably
want to avoid acrylic and go with something like fiberboard or
fiberglass. (fiberboard is like pegboard, but without the holes).
Heck, even plywood would work with angle bars!!


Some more thoughts:

I am sure that most of the ideas I come up with have also been
thought about by others like Malcolm Watts and Alfred Skrocki and
Mike Hammer, just to mention a few. Mike even asked me if I had been
spying on him :) Nope. I gues that it's just that great minds often
think along the same lines. Different actual thoughts, but remarkably
similar in many respects. When I get a really good idea I like to
work out all the details, verify it, and then share it. Sometimes I
don't have the time to do the actual full-scale build-it part before
I find it adviseable to begin sharing the thought part. Like many of
you, I am a sort of hands-on experimenter type and I love to actually
try out my ideas. I have done *enough* initial experimentation on
this idea to know that it has an excellent chance of taking care of
one of our biggest problems with capacitors: the stupid stinking air

Alfred is right: Assembly in oil is actually the preferred method
here. Mike Hammer can tell you that while assembly in oil is indeed a
messy proposition, it DOES have the positive good point of allowing
you to make really good Tesla service capacitors. 

I am fairly confident that if originally assembled in a container
under oil, that the assembled unit could then be lifted out and
transferred to a smaller container without much chance of air getting
back inside the assembly. In its new home it should ALSO be
oil-immersed. This is important to make sure that we don't get
corona/sparks around the edges of the poly, which is protected only
by the oil.

Thinking Even Bigger Thoughts...

Hmmmm. Thinking about it, *IF* the extra poly around the edges (all
four edges) were made about an inch larger than normal, and if the
assembly was assembled under oil or at least with a brushing of oil
on *ALL* surfaces (even poly-to-poly surfaces) and really bolted down
super-tight you *might* be able to get by without needing continued
oil immersion. But it seems a bit too risky for me.

But I think there is a safer way to accomplish almost the same thing.
See what you think of THIS idea:


First assemble the whole capacitor DRY with no oil whatsoever. The
initial dry assembly would be to make sure all parts fit perfectly
and smoothly together so there are no surprises. Then disassemble and
prepare for final assembly. The final assembly will have to be done
fairly rapidly as I propose having a container handy that has a
gallon of Spar Varnish poured into it. The container needs to be
bigger than a sheet of the poly or the capacitor plates being used
for the capacitor. 

(Wherever I say Spar Varnish, replace with your own favorite paint-on

(Wherever I say dunk the stuff into the Spar Varnish, you can decide
to paint Spar Varnish on instead, but it takes longer. This assembly
MUST be done all in ONE sitting!!)

It is important that all materials (poly, plates, bolts, plastic,
aluminum angle bars, any electrical connecting hardware) have been
cleaned and de-greased and are fully dry. Try not to handle any parts
with your bare hands during this final assembly, as body oils may
create problems. I would say use latex gloves that have likewise been
cleaned and de-greased. Have a big clean paintbrush ready, and lots
of newspaper and rags for cleanup.

The assembly is going to be just a bit messy, so do it in a plastic
container if possible. Or just be sloppy and get your wife upset.

Once everything is ready, begin the assembly by dunking each poly and
aluminum flashing element into the spar varnish one at a time, as we
need them. Coat completely, let drip for a few seconds, and then
transfer to the assembly bed and affix in place. Work as quickly as
you can, as we do not want the varnish drying before we do the final

(The electrical connections will be OK as soon as the bolts are
tightened down. But if that makes you uneasy, then skip
dunking/painting the section of the plate or part that will
electrically connect to the bolts.)

Assemble all capacitor elements as mentioned above, and then apply
the top compression plate. Tighten it down quickly and methodically.
Remember that you want to initially apply MORE pressure to the center
so that all air and varnish are expelled AWAY from the center.
Continue tightening until the center is at maximum compression. Then
tighten all other bolts until the whole thing is equally tight.
Attach whatever Electrical Hardware needs attaching to the plates. If
varnish gets on the electrical connection bolts you may have problems
later. Use common sense!!

Now we want to let the entire assembly dry. To make sure it doesn't
stick to the newspaper, you can lay it down on some old wood blocks
so very little of it is touching anything. Some may want to place the
assembly sideways others may prefer a parallel to earth orientation.
Do whatever turns you on.

EXCESS Spar Varnish can be removed using the paintbrush. By *excess*
I mean *REALLY* EXCESS. We actually *WANT* a *LOT* of the Spar
Varnish all over every available capacitor surface area, but
especially the edges. I would try to keep varnish off of the NUTS
used to tighten the bolts, as otherwise future disassembly would be
extremely difficult. 

AVOID the tendency to want to speed up the drying process by baking
the poor thing. To do so might introduce bubbles, which is what we
are trying mightily to AVOID here! (It also might deform any
plastic). Let it AIR DRY for at least 24 hours, and then apply
additional Spar Varnish anywhere where it looks a little thin. Pay
extra special attention to the sides of the capacitor, as this is
where the greatest danger of future corona breakout would be.

Let dry COMPLETELY now. This may take several days. Be patient!!!

You should now have a bubble-free capacitor that is totally sealed
against moisture. It is a DRY capacitor that does NOT NEED OIL!

This baby can be mounted in ANY orientation, and should be PERFECT as
a capacitor for portable applications

Common sense says you should place it into some kind of enclosure,
but in a pinch the compression mechanism will give it a fair amount
of structural protection.

As an aside: After the capacitor is fully assembled and compressed,
there should actually be almost no Spar Varnish in between the
plates. But anywhere where there is even the slightest dimple should
have Spar Varnish there rather than an air bubble.

Further Thoughts: After a compression Capacitor has been fully dried,
it *might* be possible to remove the compression apparatus and still
have the thing stay intact *IF* you have put sheets of waxed paper in
between the capacitor and the compression plates during assembly, and
IF the removal of compression doesn't cause the capacitor plates to
come apart. Once removed, the unit should be wrapped tightly with one
or more layers of strong cloth tape. Then paint liberally with (you
guessed it) Spar Varnish.  Let dry. You could then put several of
these capacitor units into a single insulating enclosure (use poly or
acrylic as insulation between units), wire them up in series or
parallel, and use them for all kinds of Tesla Coils.

Note that all the thoughts about a DRY Tesla Coil Capacitor are just
that: thoughts. I have *not* actually built such a beast. But the
more I think about it, the more I like the idea!

Hope the thoughts are useful and trigger even bigger and better
Fr. Tom McGahee