[Prev][Next][Index][Thread]

LDPE Pulse Capacitor



Hi to all,

I have come to the conclusion that the commercial "tin can caps" I'm
using are the cause for poor performance of my coil and  have been
thinking of the best approach for a polyethylene cap. I have considered
a rolled cap and a flat stacked cap. I see the rolled cap being less
efficient than a flat stacked cap for the following reasons. Rolled cap
problems are:-
1.    Requires a thick dielectric which reduces efficiency.
2.    Has more inductance which adds to the primary coil
3.    Inductance + capacitance = resonance which may reduce efficiency
4.    A long plate takes longer to discharge.

For these reasons I have opted for a flat horizontally stacked cap. I
plan to use 10mil LDPE for which I have finally managed to find a
supplier. The design philosophy is to make a block 10" x 10" using 30
plates giving +/- 0.135uF. To get the correct voltage rating (40kV for a
12Kv 60mA NST) and +/- 0.016uF total capacitance I intend to series 8
blocks. Each block will have 1/4" PVC backing plates for support. The
blocks will be placed in a PVC container and filled with mineral oil and
left standing for two weeks. During this time and to remove trapped air
bubbles I intend to apply 220 VAC for a few hours a day for the two week
period. By the way the plates will be heavy duty aluminium kitchen foil
from the local food store.
South African cost of LDPE is equivalant to $1-30 per meter (1.5meters
wide). Al foil is equivalant to $1 per box (5 meters x 0.45 meters)

Comments on the proposed design will be most welcome

Pete
South Africa