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Cap Experiments and more ?????

Hi All,

Thanks for all the answers to my cap problem. I went to experimenting further.
The new results puzzle me even more. Down below are the results

One more thing before I start: A lot of answers to my capacitance drop said
this was because of poly swelling. I am aware of this, but (I probably didnīt
make myself clear enough on this subject) my capacitance went down AS I
evacuted the container (oil already there) AND went back UP to the original
value after the vacuum was disconnected (i.e normal air pressure in the
container). I can repeat this at will and the values are always (at least
almost) the same. This makes me wonder, because if I pull out the air I must
be reducing the space between the 2 pieces of AL foil (I AM removing air), so
I would expect it to go up, not down. The values (with or without the vacuum)
will remain pretty constant (they are of course different), but they donīt
change if you compare the value with vac from day 1 to day 2 and comparing the
values with normal air pressure from day 1 to day 2.

So I think Bertīs reply to this is the one that most likely hits the nail
right on the head as to what was going on. This means the poly should be as
thick as practicly possible, but not be a single sheet. This is because more
thin sheets give a better (not higher !!) dielectric strength. If you only
have one sheet of poly (aside from not being able to roll this) and it has a
defect, it WILL die. If you have several sheets, however, it is very unlikely
that all manufacturing defects will be in the same place.

SO, What I learned was use as thick a PE sheet as practicly possible, but keep
it thin enough to be able to use more than one. I think a practicle number
would be around 6-10 sheets per layer, no more. Which is what I will do with
my "real" (read: the one I will use for my TC) capacitor. 
My experiments have also convinced me that it is worthwhile, NO, I really
should say NECESSARY to place paper in between the poly sheets to aid the oil
wicking process.

Okay, on with the new experiments:

I built another cap using just 2 sheets of poly and 2 pieces of AL foil. I
didnīt run this cap. I used only 1 poly sheet to keep trapped air to a minimum
and get rid of the problem of multiple stacked sheets not being sheet
thickness times number of sheets.

I also double checked my DMM on some commerical caps of different sizes and
types (new, old, ceramic, polarized, tantalum and mylar). The DMM showed
reasonable values for all caps (in comparison to their printed values, given
age and tolerances)

1st try)
Flat cap (dry, no oil):
Capacitance: 3.89 nF
Inductance was:  -(!) 16.63 Henry

I placed a pretty heavy book on this before taking measurements. I actually
sat right on it for another test. The capacitance went up, but.... read on.
The connections were put in the middle of the AL sheets (just another small
piece of AL, to keep everything flat). Iīm not sure what my DMM was trying to
tell me with the minus sign.

Now I rolled up this cap as tight as I could (was about the size of a pencil)
and remeasured it. WOW !!

2nd try)
Rolled cap (dry, no oil)
Capacitance: 10.33 nF
Inductance was:  +(!) 5.98 Henry

The electrical contacts were in the same place and I didnīt move either of the
AL sheets around while rolling it. Now if the two AL plates would act
capacitativly on each other, it should have gone down, not up. (I think). When
I put my weight on the flat cap I got about 4.5 nF, still nowhere near the now
(rolled) measured 10.33 nF.
If I take the plus and minus values on my DMM into account the inductance of
the rolled cap did go up (as I expected). What really puzzles me is the
gigantic increase in capacitance.

Just for fun of it I plugged the values into different TC progs. Yep, you guys
guessed it.... more different values. 

They gave me these values (give or take a few pF):

AL plate size: 6.89"x16.43" 
(Measured thickness 12um = 5*10^ -4 inches= 0.5mil kitchen foil)
PE foil thickness: 1.75 mil (measured)
PE K value: 2.2 and 1.0 (guessed values)

Calcīd capacitance should have been 63.75nF (for K=2.2) or 28.9nF (for K=1)

What the -at-+!!!!###-at- is going on. I mean a K of one IS PURE AIR, How can I go
below 1 (in terms of dielectric insulation K of a plastic) What should I
believe now ? 
Where are those germlins hiding?!?

This is really starting to tickle me silly. I havenīt gotten around to trying
this with my 6.7 mil PE sheets (yet !!!). 

And yes, I am definately sure the thin stuff is really made of PE. At least it
says so on the enclosed piece of paper.

I am beginning to suspect that you cannot just "go and build" your own
capacitors.

Tell me what you guys make of all this and lemme know.

Coiler greets from germany,
Reinhard

BTW Bart: No need to apologize. I hope I didnīt "mail you too hard". I was
just wondering if I was perhaps overlooking the obvious. We all make mistakes
and this makes us learn something. Remember my inquiry about the secondary
frequency of a coil (I used wire length, 1/4 wave stuff, etc) ??? I sure felt
like a dummy after realizing what I hadnīt taken into account something very
obvious (capacitance and inductance values for different size coil diameters).
Thatīs what this list is for. To help all of us crazy guys out there. Imagine
what a job this would be if you had to dig up and/or work out everything that
has been said and /or done by all members on this list. Plus you get such a
variety of ideas.

At this point I would also like to say a BIG thanks to Terry for mastering
this piece of Internet art, that IS of REAL help.

Quite unlike the Tesla-USA List from which I unsubscribed long ago.