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New Cap Type
Hello All,
Iīm not sure if I "invented" something new, but I thought I would let you
know:
My cap design looks somewhat different from the rest of the poly design types
I have seen. In the process of building and testing different homemade caps I
found out something very interesting. If you build a poly cap the conventional
way you need lots of PE foil in order to prevent your cap from dying a high
voltage death.
I stack my caps this way: 2 pieces of PE foil start the cap pack and 2 pieces
end the cap stack. In between this I alternate aluminium and PE, but I donīt
interconnect any of the AL plates. I just connect the lower and the upper
plate of the "cap". My idea behind this is very simple: If you do this, you
are really connecting multiple caps in series (i.e AL PE AL being one cap).
This way I use only one piece of PE foil, making the whole thing easier to
roll because the AL sticks nicely to the PE and you donīt have PE on PE
slipping all around. I say my PE foil (6.7 mils thick) will hold up to 500
volts AC with ease. So e.g. if I want a 10kv cap I would need 20 PE foils. I
build one of these prototypes and here comes the killer: I fired it DRY in a
TC tank. It took it with ease. After about 5 mins of running it was barely
warm and NO corona or arcs between the plates even though I was putting 15kv
(50% overrated) into it and used NO oil.
The thermal and electrical stresses are greatly reduced, compared to the
normal poly design. The only negative thing about my design is that you need a
lot of these to make your needed capacitance. However, I would be able to fit
at least 5 or 6 of these 2nf (protype case) caps in a single 4" PP pipe and
connected them in parallel for 10-12 nf. My pickup plates are placed in the
middle of the top and bottom plate. My idea behind this is simple, too. As I
take the current from the middle of the plate, the inductance of the end
plates is smaller and the current doesnīt have to follow a single long path to
the discharge. So my cap should be able to discharge quicker than a
conventional rolled design. Which translates to a better bang for the money.
Besides, itīs easier and faster to add (they can be built in about 15 minutes
time) or subtract a cap or two to change my capacitance (for tuning), than if
I had one or two big poly rolls.
Has anybody else tried this or have comments?
coiler greets from Germany,
Reinhard