Help with Custom Cap thoughts??
From: djQuecke [SMTP:djQuecke-at-worldnet.att-dot-net]
Sent: Wednesday, April 01, 1998 4:53 AM
To: Tesla List
Subject: Help with Custom Cap thoughts??
I wrote to the list several months ago about a material I want to try for
building custom capacitors. As usual, I have taken what seems to be a
fairly simple task and turned it over in my mind for so long that I'm now
thoroughly confused about the basics.
If you would bear with me I'll try to explain myself and perhaps get a
couple of rather simple questions answered.
The material is called ALPOLIC. It is maybe a 3/16" thick piece of
polyethylene sheet with perhaps a 1/16" thick sheet of aluminum bonded to
each side. It comes in 4' x 8' sheets and you can use wood working
equipment to cut it, etc.
Pluses: zero air gap between poly and AL. Poly is thick enough to withstand
high voltage. Works fairly easily.
Minuses: The AL sheets have a special paint bound to their surface which
doesn't remove easily. Poly perhaps too thick. Electrical connection
between plates has me confused.
The following ASCII drawing (sorry) shows 3 plates connected together. The
easiest manner to connect them would be with UMW rods (E1 and E2) and use AL
bushings between plates for the necessary electrical connection.
Assume the conductive AL plates C2 and C3 as well as C4 and C5 are connected
by AL bushing placed in between them. The UMW rods slide thru the centers.
Each plate will have two holes 3/8" diameter for the rods to bind them.
I'll remove a 5/8" ring of AL on center with each 3/8" hole to avoid arc
thru holes. Between twinned plates I will place a 1/2" ID x 5/8" OD x 1/4"
thick UMW bushing over the 3/8" UMW rod and then place a 5/8" ID x 3/4" by
1/4" OD AL bushing over that.
I'll remove the paint only in a 1" circle center on the holes between
Each plate is about 5" square. I'll remove a 1/4" strip of AL along all
edges on each side of plate to avoid arcover around edges.
I'll remove paint around holes/rods on end plates and connect leads to each
end. The UMW rod ends will be threaded and I'll use nylon nuts to hold it
In this case then the conductive plates C1, C4 and C5 are positive plates
and plates C2, C3 and C6 will be negative (don't forget these "conductive"
plates are actually bound to the dielectric plates and it can be confusing
to refer to them separately).
This requires that an odd number of plates be connected together so you a
pos and neg end plate.
I figure 25 plates per cap. Should be about 12-13" long, 5" square around.
I'm hoping for .0025uF per cap and a voltage rating of at least 50kV and
perhaps actually more like 100kV???
I've got to get a micrometer and find out how thick this stuff actually is.
Q1: Does this have chance of working? <g>
Q2: In this scenario do I get to count the surface area of both conductive
plates C2 and C3 or just one because they are in reality joined?
Q3: Do plates C2/C3 have to be physically connected to the end plate C6 and
does C4/C5 need connected to C1.... or does the current pass thru C1 then
D1, C2 & C3, D2, C4 & C5, D3 and finally C6??
Q4: Doesn't my design actually just connect 3 capacitors (plates) in
parallel? (I hope it is really that simple and I've just made another
mountain out of a molehill, my specialty.)
Q5: Assuming it works at all, is there a chance they will work without an
oil bath. I just don't see the necessity for oil since AL is bonded to poly
(no air gaps there) and corona would have to jump either 11/16" inch of air
around edge to avoid 3/16" poly or jump 7/16" thru holes to avoid the 3/16"
poly. Or is that what can happen by "surface effect" and the oil somehow
Q6: I got this material though scraps at a construction site. I need to
check pricing but wouldn't it be really easy to just buy a 4' x 8' sheet and
rout off a 1/2" strip of the AL on both sides, place one electrode on each
side at opposite ends, get about .0085uF and call it finished?? A tad
unwieldy but hey, I like the labor level......Of course you pole pig types
will need to stack a half dozen of these....
Thanks for your time,
Not to Scale
Must be viewed with a fixed pitch font.
Pos End Neg End
___ ___ ___
_ | | _ _ | | _ _ | | _
| || || | | || || | | || || |
|C|| D ||C| |C|| D ||C| |C|| D ||C|
|1|| 1 ||2| |3|| 2 ||4| |5|| 3 ||6|
| || || | | || || | | || || |
|_|| ||_| |_|| ||_| |_|| ||_|
|___| |___| |___|