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Cap question???
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From: Gary Lau 09-Feb-1998 0818 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Monday, February 09, 1998 7:37 AM
To: tesla-at-pupman-dot-com
Subject: Re: Cap question???
From: Zuma [SMTP:mwise-at-ns.sosis-dot-com]
>I have finally decided to build some poly caps. I have come to the
>conclusion that I am going to construct .005uf caps using 60mil poly.
>They are going to be rolled caps. I have also decided to go with a very
>small size (2"x160" plates, 4"x166" dielectric). I know this may sound
>stupid to make caps this small, but I want to make my caps in intervals
>of .005 and use the smallest amount of space at the same time. I am
>planning on the plates being aluminum tape or aluminum foil which ever
>is easier. If I use the tape my question is should I leave the paper
>backing on the tape or attach the tape directly to the poly? I am hoping
>someone will help with my question and not "dog" the idea.
If you're planning on using 30 or 60 mil poly, it'll be tough to find a
contiguous piece 166" long, it generally comes in 4'x8' sheets. If
you're using the 6 mil drop cloth material, good luck keeping it all
lined up when rolling! You generally have to allow much more that 1"
margins, particularly when using many thin layers, to allow for less than
perfect layer alignment. Additionally, having the plates that long will
add significant inductance to the caps, something one tries to avoid in
pulse-discharge cap applications.
Having such a narrow plate width also makes for a very poor efficiency in
terms of poly usage, half of your's will be used for edging.
Applying the tape directly to the poly may be a good idea as it
guarantees that the plates won't shift when rolling. The only down side
I can see is that you can't make the plates any wider than the 2" that
the tape comes in. It will also be challenging to make a good high
current connection to tape.
Gary Lau
Waltham, MA USA