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Proposed capacitor design
I am seeking opinion and sage advice regarding design and construction
of a cap.
I plan to make a stack cap from 9" X 13" impact-resistant styrene
cutoffs I can get at a very low price. The material is 20 mil thick.
For use with a 15kV, 60ma NST, I expect that six 0.06 uF caps made
with this material, potted in oil, and wired in series would suffice.
Is this too conservative? Not conservative enough?
If the stacks are under oil (I have Suniso refrigeration oil and Diala
AX on hand), is a 2" guard region between the edge of foils and
dielectric really necessary? Going to a 1" guard region will reduce
the number of dielectric layers from 50 (for 2" guard region) to 29
layers. I plan to round the corners of the foils.
I have samples of the styrene under the Suniso, castor, and mineral
oils. I haven't seen any damage thus far (2 days at room temp).
Various reference differ as to compatibility of styrene with mineral
oil. Should I not use mineral oil with styrene?
Also, what enclosures would be suitable for such a cap. I'd prefer to
not use Rubbermaid containers. Would a particle board/MDF box,
painted with polyester resin be resistant to mineral oil?
Just for fun, I made a quick 0.01uF cap (20 mil single layers) with
this stuff and wired it in series with an NST and a Jacob's ladder. I
expected it to fail, and it did, but before its demise I was treated
to a rather fierce and noisy spark across the ladder. The spark
climbed higher than it did without a capacitor in the circuit. The
cap's mode of failure was numerous discharges along the surface of the
dielectric layers (the carbon tracks rather pretty), followed by a
rather vicious punch-through near the edge of a foil. There were also
several 6" long discharges along the exterior of the cap, with the arc
between the clips that both held the stacks together and acted as
terminals.