Re: Blown Cap

Luke all,

> David;
> I recently had a home made cap fail. It used 90 mil poly and was
> connected to 15KV neons..
> It failed right at an edge of the plates.
> At least two of us have had failures at the same point.
> I wonder if it might have been caused by an air bubble? The edge of
> the plates would be a natural place for a bubble to get stuck.
My point in relaying my Cap story was because I am questioning the voltage
ratings we all have been applying to LDPE. Homemade Caps will never be
completly free of defects be it air bubbles, dust and other debres. I
for one do not have access to a "clean room".  So I would sugest over
engineering. The voltage ratings that I have seen being used for TC Cap
design I believe are coming from standard texts with an extra margin of
error thrown in and not true to RF. I would venture to sugest that when
one is designing a Cap to be used in the 15KV region that it would be
best to use 120 mill LDPE, and since that added distance between plates
would probibly hinder performance, place two 60 mill in series. I know
this has been common pracise for many of the pros here, but just thought
that I would throw out the sugestion/warning to those about to spend
almost a $100 to build a Cap.
 Ok, now I have question for those who have ordered from Condencer
Products, as I am now thinking of ordering a Cap: What advantage was the
group order? Savings in shipping, or is there a minimum order? I would
be looking for something in the .015 mFD -at-15 KV (Coil rating of course)
so would I expect tp pay around $200? I will call them after the weekend
but would like to hear from any body who has delt with them first. Can't
really afford it right now, but whats those nasty credit cards for?!

David Trimmell <dwt-at-efn-dot-org>