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Re: HomeMade Poly Cap
Tesla List wrote:
>
> Original Poster: "Michael Novak" <acmnovak-at-execpc-dot-com>
>
> Hi All,
>
> In the coming weeks I plan to make a rolled poly cap for my medium
> power TC...
SNIPPP
>
> -Michael
Hi Michael.....
before you go and build a rolled cap ... consider the MMC caps. By the
time you buy the materials for a rolled cap you will be spending nearly
as much or even more than a MMC configuration.
to be safe with a rolled cap you will need about 60 mil minimum of
dieletric between plates ( at 4 mil thats 15 layers for each set and you
will need 2 sets e.g. 30 layers total ) then there is the cost of the
foil, the pipe to put the cap into, the oil to help insulate it and
thats just to do one cap.
rolled caps NEVER roll right the first time, the sheeting slips and you
reroll it about 5 times. and besides when rolling it, it creates static
electricity and it becomes a dust magnet. Dust = easily damaged cap.
if you get past that part without wanting to destroy it, then you will
need to contain it in the pipe and oil. If you have access to a
commercial vacuum pump then you are half way home. AIR is the prime
enemy of rolled caps, if there is any air left between the sheeting, it
WILL form corona and a hot spot. And a hot spot = certain death for the
cap.
If you blow the cap, repairing it is a real pain in the butt. You have
to unroll an oily drippy messy cap and replace the area that arced out
with overlapping sheets which makes the cap roll even more difficult
after the fix.
If you are really interested in making a homemade polycap, make the
plate cap style. you can cut several sheets at one time, they are easier
to put together, if you blow it, you can repair it alot quicker. as far
as air problems, put the cap into the container add oil, let sit for a
day or so and then slide in some extra material on the ends. this will
compress the plates more and increase the uF's. ( being that the cap was
in the case loose allows the air to settle out faster). But still, it is
messy with the oil.
If you want easy construction, hi quality, less chance of a cap dying,
and reliability... MMC
been there done that ( making homemades) never will do it again.
Scot D