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Re: New cap info
Tesla List wrote:
>
> >From DavidF4797-at-aol-dot-com Thu Dec 5 00:15:59 1996
> Date: Wed, 4 Dec 1996 14:03:22 -0500
> From: DavidF4797-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: New cap info
>
> To All:
<BIG SNIP>
> 4) When building capacitors in mineral oil (without a vacume pump to remove
> the air bubbles) the plates should be no more than 3 inches long in any
> direction (for flat cap designs) or more than 3 inches wide for rolled caps.
> This is because dielectric more than three inches wide will end up with dry
> spots which will heat and eventually cause cap failure. This is because the
> capillary action of mineral oil cannot easily penetrate more than 2 inches in
> any direction between plastic sheets. (I noticed this effect in my flat cap
> the first build (which has 8.5x11in plates)).
>
> 5) If you are determined to use a plate/dielectric size wider that 3 in, you
> must then use paper to wick the oil farther between the layers (I conclusion
> I came to myself when building mine). This works well up to a 6 inch plate.
> Alternatively, If you use use *silicone* oil instead of mineral oil, you
> may then dispense with the paper. This will also work well to about a 6 in.
> plate.
>
<BIG SNIP>
>
> Hope it is usefull
>
> -DavidF-
David,
Great post! Sorry about your cap. But I have a few suggestions that you
may find useful, if your still interested in homemade caps.
While stacking your plate capacitor, use an eyedropper to spread
liberal
doses of mineral oil between the poly and aluminum sheets. This will
eliminate those
dry spots you spoke of (I discovered this after I had burned a
development cap I
built.). And, another suggestion is to use Aluminum flashing if
possible, store bought
Aluminum foil is a bit thin for robust construction techniques.
The stacked plate cap I'm currently using I built over a month ago now
and
I have more than 8 hours of run time on it. I can't say I've used it
with a rotary
but I have tested it using a 10 KVA 14400 pig, a variac, and a really
big Jacobs ladder.
I have'nt seen any corona under the oil yet (Cross my fingers.).
The moral of the story is simple, when building your own flat caps.
a) Wet down the components with oil as your stacking the capacitor.
b) Make sure your plastic sheets overhang your Aluminum by 1" or more.
c) Round and sand paper all of the edges on your Aluminum sheets to
prevent corona.
d) Use a container, for your cap, that will provide pressure release
in the event of a failure.
The above technique can be messy but it works. Oh by the way, what does
your
friend at the cap factory want for his HV capacitors?
For example:
0.1 uF 100 KVDC $?
0.01 uF 100 KVDC $?
0.001 uF 100 KVDC $?
Last:
Always remember and never forget, why coilers build homemade caps in
the
first place. $
D. Gowin