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Re: capasitors..


On Wed, 20 Sep 1995 tesla-at-grendel.objinc-dot-com wrote:

> to ask is what specs The cap(s) should be rolled to for
> a .007ufd value.  I know that this is hit or miss for the
> most part, but an idea of roll length using 14" wide al 
> flashing and 90mil poly would be nice if possible.

My cap made of 1.6mm thick (about 60mil) polypropene used 33cm width
copper-plates, two of them, each 1 meter long with di-electric
length of 1.2meters. I hope this helps as the cap is quite
exactly 7nF.. It was rolled like the bigger version of Richard.

btw: my next cap will be a stacked one with the construction goal
of 40nF 30kVAC pulse.. It will be physically huge :) but necessary 
for my magnifier design.. (210kHz secondary) 

The other project with up to 100kVAC (rms) input will need an
interesting capasitor as well..

Anybody out there with the information about using xformer oil
as a di-electric: how lossy will it generally be? It's one of
the easier options for getting the required voltage-rating when
the voltages are extreme like 100kVAC.. Please note that I'm
not provoking the use of old surplus etc. oil-filled caps but
making them with a good plate-configuration etc.

about pcb's : I was told when I got an old xformer that had been
constructed in the 50's and has some pcb-oil as insulation that
pcb's aren't really that dangerous unless you drink the oil :) or
_burn_ it - that's how the nasties are formed according to him..
It's quite logical : for an xformer fails it will generate heat
and thus the pcb's will get hot/burn and _voila_ - nasty chemicals
will form.. (the above about pcb's just as I was told, not verified)

Yours,

  Kristian Ukkonen.