BIG Bucket Capacitor

From: 	Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: 	Sunday, July 13, 1997 5:26 PM
To: 	tesla-at-pupman-dot-com
Cc: 	Michael Smith; Tesla-2
Subject: 	BIG Bucket Capacitor

Fellow Coilers,
Fr. Tom here again with an idea for all you Dumpster Divers out

My good friend Michael Smith brought up the topic of the Ice Cream
Capacitor, and mentioned that he would like to find a way to use the

Forget about melting them or even trying to flatten them out, as the
heat will change the chemical structure, and the flattening will
cause stresses that will weaken their effectiveness under HV stress.

BUT, let's apply the practice of ZEN here, and instead of trying to
force the stuff into becoming something it ISN'T, let's use it the
way it already IS!

The "BIG Bucket Capacitor"

This is just my first-level run through of the basic idea. I have
*NOT* built one of these yet. But I offer my still-shifting thoughts
on the subject in the hope that they may be found useful by at least
one of my fellow Dumpster Divers. Modify this design to your heart's

*** Note *** the following method is probably not going to work out
efficiently with small ice cream tubs, but it should be quite
effective when applied to *LARGER* containers such as large plastic
buckets and even polyethelene garbage cans and those humongous
industrial strength plastic DRUMS!! Every place where
the text says "bucket", think "Big Bucket"! The bigger the better.
This method scales UP better than it scales DOWN!! (Adjust actual
dimensions accordingly. Use common sense!!) The reason it scales UP
better is that you will always need an inch or two more of poly than
metal plate because of the need to prevent arc-over along the edges
and ends. On something the size of an ice cream tub that is a
significant percentage of the available poly surface area "lost". On
a garbage-can sized scale, the "lost" area is a much smaller

Also, the method can be easily extended to using regular
flat poly sheet. But the *REASON* why I cooked up this method is
specifically to make use of poly that is already curved and otherwise
unuseable by coilers for making capacitors. This is not necessarily a
"better" way to make a capacitor... it is just a way that allows us
to use a resource that would otherwise not be useable at all.

For the sake of discussion, I will assume in the following
description that we are using a bucket with a diameter of 12".
Further assume that said bucket is 17" tall, but that only 14" of
this height is perfectly smooth. The upper section has yucky ridges.

So here's the idea. Take a dozen or two of your identical buckets. I
will assume a true cylinder here. Cut the bottoms off of ALL of the
buckets except ONE. This one will be the "container" for all the
rest! When you cut the bottoms off, do so by cutting through the SIDE
of the container about 1/4" above the base of the container. You can
make a simple tool from two small pieces of 1/4" thick plywood that
can hold the blade from a utility knife or a piece of hacksaw blade
so that the cuts can be made very easily and uniformly. Have the
blade sticking out a distance that is just slightly *more* than the
thickness of the material to be cut through. Clamp this tool to a
flat surface. Place the bottom of the bucket firmly flat on the same
surface and then engage the base against the tool while turning the
bucket smoothly and firmly. The idea is *NOT* to cut the base off in
only one turn, but to remove a bit of the base SMOOTHLY and UNIFORMLY
each turn. 

The SAME or similar procedure should be used to remove the top of the
bucket as close to the yucky ridge as possible so that we get the
largest smooth flat section of the bucket cut out as possible. A
hand-held hacksaw can be used here, because the ridge will help you
keep the cut neat. 

OK, so now let's assume that you have a container bucket and a bunch
of buckets with the tops and bottoms trimmed off as described above.
Now we have to remove a slice of material down the side of each
bucket. (The "container" bucket is NOT to be modified in any way). 

Take bucket #1 and make a slit that is 1" wide from top to bottom.
Now slip this bucket section INSIDE the container. It should squeeze
inside, but now the gap will measure LESS than 1". Measure the actual
gap width and then carefully cut off the excess such that when
inserted, the gap is again 1". Leave this section inside the
container bucket. Now take bucket #2 and do the same thing, except it
gets inserted inside bucket #1. When you insert it, you will see that
the gap is smaller. Measure how much smaller it is, and then
carefully cut off the excess such that when inserted, the gap is
again 1". Ensure that the gap spacing is consistent. Do the same with
each additional bucket, building up concentric rings that grow
INWARD. Keep the gaps so that they are all 1" wide. This 1" gap will
later help us to keep the plates properly oriented inside the
container bucket, and will also be the place where the electrical
connections are made to the ENDS (hint hint). It is better to have
the gap slightly larger rather than smaller than 1", as two pieces of
1/4" thick plexiglass will eventually be inserted in the center of
the gaps to provide hard insulation.  

Continue adding bucket sections until you can no longer insert a
piece of 8" diameter PVC pipe inside the middle. You can use
something other than 8" of course, but there is a law of diminishing
returns here, and on a 12" diameter bucket, I would guess that you
would want to stop at about 8" in diameter.

OK, so now you have X number of polyethelene sections each trimmed so
that they can slip inside one another, and a PVC inner pipe. The idea
now is to remove all this inside stuff and then re-assemble, but THIS
time with metal plates in place. 

There are many different ways you can handle the problem of getting
the plates aligned and getting the connections made. Use your
ingenuity, and don't forget to allow MORE than adequate spacing
around the edges of the poly so you don't get arc-over!!

I am pressed for time here, as I have to get back to my summer
assignment, so I don't have time to give a complete piece by piece
description on how to assemble this into a complete working
capacitor. But I know that some of you will take this up and fill in
the missing details for the others.

*** Just a few quick HINTS. 

Bottom needs radial 1/4" thick plexiglass support structure so oil
can circulate along bottom.

Make a plexiglass shield 1/2" thick using two sheets of 1/4" thick
plexiglass (cheaper than 1/2"). This shield will extend from the
inside wall of the container bucket all the way through the middle of
the gap INTO the center of the central PVC pipe. That means that the
PVC pipe should have a 1/2" wide slot cut down the length of one side
of PVC pipe (or wider, so the PVC can flex a bit!) The bottom of the
PVC pipe should be beveled to make final insertion easier. 

Coat poly and plates with oil as you assemble and reduce the time it
takes to get this baby operational.

Make sure the metal plates don't shift and CAN'T shift within the
next X number of years.

The electrical connections are made from the ENDS right next to where
the big plexiglass shield is. Think "C" curve when you ponder how the
capacitor plate ends will all make a really good WIDE RF contact.
This allows you to make a sneaky COMPRESSION electrical connection
using a piece of flat aluminum flashing and anything thin and robust
that you can hammer into place next to the wall of the plexiglass.
(Try stuff like fiberglass board and leftover PC board slabs cut into
strips of the proper width. Beveling helps!) Be creative, guys!!!

Oh yeah, to conserve transformer oil, visit your local plastics
dealer and dumpster dive for all the stupid SMALL plastic garbage you
can shovel INSIDE the PVC pipe AFTER you ram a big wad of cloth down
the inside to plug up the end. Fill PVC almost to the top and then
plug up the top of the PVC with another rag or plastic disk with
HOLES in it. Think CHEAP!!!

I suggest electrical connections out the side of the bucket about an
inch below where the top overlaps. BIG Bolts and RTV Silicone...

This allows the top to go on more readily. Add vacuum/oil entry
fittings if desired. Seal it up. Vacuum and fill and vacuum (or
whatever else it is that you like to do...). {The vacuum will help
SQUEEZE out air, because the outer wall and the inner PVC act against
one another}

Then ENJOY using your really TRASHY "BIG Bucket Capacitor" 

Fr. Tom McGahee

Looking forward to sending out more Trash next week!