Singing them ol' capacitor blues
From: Larry Robertson[SMTP:LWRobertson-at-msn-dot-com]
Sent: Wednesday, June 18, 1997 1:46 AM
To: Tesla Builders
Subject: Singing them ol' capacitor blues
Hey ... long time no write - been struggling with capacitor manufacture.
BTW I phoned Condenser Products for a quote on a 0.025/20kV cap.,
the price went up to $340, so I decided another round would't hurt.
I've been so careful with this one, and spent so much time bringing
it up I named it "Baby".
This time I used 3 sheets of .030 polypropylene as dielectric, 24
inches wide, and 20 inch AL flashing as the plates. I found an
arrangement that caused the plates to extrude on the outside
of the roll separated from the poly, and 90 degrees from each other.
I used a friction connection with 1 inch strips of the same flashing
all the way up as the leads, all well taped down. Man, is that
tough to roll up tight enough to fit in a 6" pipe.
Measured on a Fluke 87 at .018.
Then I took my pail of mineral oil and the sealed capacitor to
work and applied a vacuum pump for about 45 minutes. The top
plate bowed in by about 1/4 inch, but held. I guess I'll use thicker
Plexiglas on the next one - this was 1/4 " thick, 6 inches in
diameter, and the air pressure at 15 PSI atmospheric could have
been as high as 400 lb..
The mineral oil foamed furiously when admitted, and continued to boil
for the next hour. I backfilled four times with dry nitrogen gas.
Although the outgassing slowed, it was still at a medium boil after
an hour and a half, so I thought I was either pulling off lighter
fractions of the oil or sucking air through the PVC container
so I vented it with N2 and held it gingerly all the way home.
On a pumped capacitor, I don't understand what breaking it in
will do, but I did it anyway. In fact Sargeant mentions breaking
in commercial capacitors, so something must transpire.
( And by the way - which one of you toads got that pristine
copy of "High Power Electronics" from Justin's Books last
week while I was out of town doing honest work. I phoned the
store and they said seven people called the same day it was
offered.Finally went for $112.)
Another by the way : pursuant to my last short post, a
schematic of a solid state pulse generator is on a Russian
site : www.dux.ru/guest/exci/power.html .
So I'm running Baby at about 18" of spark for a day or so. It
is a very quiet capacitor, even at 10 kV straight across the
transformer it doesn't make any corona noises at all. The
spark gap noise is different too. My first cap. had the plate edges
sticking out and shorted turn for turn on each end and had huge
5 Mhz parasitic oscillations as observed on a 'scope nearby.
Although I find it hard to believe those would be aurally detectable,
something about the spark seemed snappier. Seems to be
performing similarly though.
This time I tried a safety gap across Baby, at least initially.
When that goes off it is ten times louder than either the main
gap or the tesla discharge. A ball of green plasma surrounds
the copper gap, and inspection reveals all oxide blown
clean off for about 1/4 inch.
Ain't coilin' wonderful!
Not enough power in ...
Morgan Hill, CA