Back in 1993 I learned that Chicago was home to Plastic Capacitors, Bycap
and Chicago Condenser. I had already been requesting tours of any place I
could get a tour of. I first visited Plastic Capacitors. I was very excited
about what I saw that day and went home and immediately started to make my
own caps. I used aluminum foil and the plastic sheet covers with three holes
and the black paper insert. My best guess was this plastic was polystyrene.
Nobody has disagreed with me yet so it is still polystryene. I made only
single layer caps but was able to charge them using the flyback of my
computer monitor. I was never able to measure the voltage, but I was able to
store a 3/4" spark that could numb an hand or arm for a bit. Even back then
corona was my enemy. I tried impregnating the rolled up caps in parrafin but
that caused too much leakage for some reason. These capacitors showed lots
of hysteresis. It was almost hard to completely discharge them.

I was granted a tour of Bycap which is spin-off of Plastic Capacitors. I
spoke with an engineer from Hipotronics in Ney York as well. I was amused
that three different companies made the same products in sometimes
completely different ways. For ethical reasons I will not discuss these
differences. Hipotronics send me several rolls of capacitor foil and 1mil
polypropylene film. I tried winding and vacuum impregnating my own
capacitors using mineral oil. I leared quite a few things first hand. Dust
of any sort is really bad for a film capacaitor. it's hard to fill the voids
around dust with oil. This lets corona destroy the film. I noticed that when
I tested my windings before impregnation using AC a weird white film would
form on the polypropylene film. It amlost looked like condensation. I am
told this may have been oxidation of the platic from corona and byproducts
of corona in air. In any case, this white film was a bad and meant things
were going to fail. There was lots of failure. Many caps failed where the
edge of foil touched the film. Some places cut their foil with a laser so
the edges are completely smooth and do not introduce large electrical
stresses on the film.

I also quickly learned that you do not use mineral oil and polyproylene. My
capacitor sections would "dry up" and become wrinkled and weird looking
after some time. It turns out polypropylene absorbs and is dissolved by
mineral oil. This was confirmed by the engineers I spoke with as well. I
should have used castor bean oil. This seems to still be a favorite for use
in energy discharge and pulse duty capacitors. I have never worked with
castor bean oil yet. It is suppsed to be quite hygroscopic. 

I still have a few of the capacitors I made. If found, I'll Krodak them.


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