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Re: flat caps



In a message dated 97-02-14 01:57:41 EST, you write:

<< 
 If this size MYLAR is not acceptable for a flat cap.
 
 What size plates do i need for a roll cap with 30 mil polyethylene
 
 and aluminum flashing at .01 uf?
 
 
 
                        Darren Haley
  >>

Darren,

Mylar is not a good material for Tesla tank circuit capacitors.  Polyethylene
is excellent.  I have only made rolled poly caps.  Some quick calculations
using the formula C = .224 K A / d  (where C is in pf, K = dielectric
constant of poly (use 2.0), A = area of plates in square inches and d =
distance between plates in inches) indicates one stack of 4 plates with .030
poly between each would be equal to .001 mfd with 10" square plates.  You
would need 10 of these in parallel to get .01 mfd.  I used one stack of three
.030 plates because you need at least .090 to withstand 15 kv.  You might try
other combinations to get a smaller total package.

I like the rolled caps now that I have built a few.  A rolled cap will
produce twice the capacitance from the above formula - i.e. total finished
capacitance will be twice what the formula caclulates.  Using three layers of
.030 for a total thickness of .090 in a rolled cap, you would need plates of
1010 square inches / 14" (std. width of roof flashing) = plates 72.14" long
for a .01 mfd cap.  You also need to add about 4" to the length of these
plates because of the way they roll up, you actually lack about 4" where the
top doesn't overlap the bottom plate.  You should roll this cap before you
make the container for it (usually 6 or 8" dia pvc pipe) because it will be a
large roll.  You might also consider making two .005 mfd caps like this and
use them in parallel.

I recently made one that is .00475 mfd with two layers of .062 poly (for each
layer) and those plates are 47" long.  This cap just barely fits into a 6"
pipe section.

Ed Sonderman