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Re: Cap Question
Doug,
The Java calculator is on my page. It was written by Jerry Gore. I put in
the note
regarding manually multiplying the result by 2 for rolled caps thanks to a
coiler
who identified the problem. Why? Because the original calculator did not
take into
account that a 2 plate rolled cap when rolled has 4 conducting plates (each
side
of the 2 plates serves as a conductor in a rolled configuration) as my note
on the
page identifies.
I went out to the Java calculator page just now and put in Reinhard's
values. The
Java calculator calculated a capacitance of 5.47nF. Now, you see why I put the
note on the page. Multiply this by 2 gives the value of 10.94nF, pretty
darn close
to what Reinhard is measuring.
BTW - if anyone finds any problem with the Java calculator, please let me
know. I
personally don't use it, but I keep it out there for others who might. If
there is
a problem I would like to correct it in the java code if possible.
Bart
Tesla List wrote:
> Original Poster: Doug Brunner <dabrunner-at-earthlink-dot-net>
>
> Aaack...
> I'm not sure what would be happening, but one thought did occur to me. On
> the Java
> tesla calc page, they've supposedly got an error in their formula that
> results in
> it putting out 1/2 of the correct value. Maybe the people who did the
programs
> you're using took the already corrected formula, and multiplied the whole
> thing by
> 2. Looking at the fact that 10.5 is one-half of 21, it looks like more
than a
> coincidence. I'd say, just build another cap like it, unless it's too
> expensive,
> in which case I'd say build some SW caps. I haven't heard about them having
> problems, even with big coils.
>
> Hope this helps!
>
> Tesla List wrote:
>
> > Original Poster: RWB355-at-aol-dot-com
> >
> > Hi All,
> >
> > Iīve got a really wierd problem. H E L P !!!!
> > I decided to "oil in" one of my test caps. So I bought myself a piece
of PP
> > pipe, two end caps and proceeded on.
> >
> > The cap specs:
> >
> > Al foil: (2x) 78.74" long and 11.8" wide
> > PE sheeting: (2x) 24 sheets of 1.75mil PE (42 mil per set)
> >
> > I started with 24 sheets of PE. Next is one AL foil. Then again 24
sheets of
> > PE and stopped with the last AL foil. I used a wooden rod to roll the
> thing up
> > nice and tight. I didnīt have very much slippage (PE sheets) and it
ended up
> > rather nicely.
> >
> > Hereīs a bad ASCII Drawing:
> >
> > _________________ AL foil
> > _________________ PE (24 sheets)
> > _________________ AL foil
> > _________________ PE (24 sheets)
> >
> > I put some tape and wire ties around it and removed the wooden handle. The
> > electrical connection where placed in the middle of each AL foil sheet
> (across
> > the full width). I figured this would give me better discharge and
> inductance
> > values.
> >
> > Here the mystery starts.
> >
> > 1.) I had calcīd this cap to be aprox 21 nF. It turned out to having only
> 10.5
> > nF. Thatīs only one half. I scratched my head, unwound the whole thing and
> > tried to rewind it tighter. It didnīt help at all. Why? Is there a
> possibility
> > that the two AL sheets are acting capacitivly on each other, because I
> didnīt
> > cover the top AL foil with more PE sheets effectivly reducing the
> expected 21
> > nF to the measured 10.5nF ?!?. I donīt think so.
> >
> > 2.) I plunged it into my PP container and filled her to the rim with
mineral
> > oil. The capacitance didnīt change at all. I ran a line from the vacuum
port
> > to a glass full of oil. From the glass I went to my trusty vacuum pump
> (an old
> > fridge pump...works pretty good for the $10 it cost me). Next mystery. I
> > pumped it down and measured the capacitance while pumping down. I
figured it
> > would go up as trapped air was being removed. Nope, it didnīt!! It
actually
> > went down aprox 2nF in the beginning. After 30 min of running I removed
the
> > vacuum pump and let the cap suck back the oil in the glass jar. There was
> > still oil left after the vacuum was back to zero, so I figured it was
> (almost)
> > full. The cap now measured 10.8nF. !!#~-at--at--at-##+!! I reconnected the vacuum
> pump
> > at let her have it another 30 min. As the pump started making vacuum
again,
> > the cap value started to drop again, stopping at aprox. 10.2nF. I redid
this
> > twice more. I let the cap stand for two full days and measured it
again. Now
> > it has 10.95nF.
> >
> > 1.) Why doesnīt the cap have 21nF or at least somewhere near this?
> > 2.) Why didnīt the cap value increase, as it was being filled with oil. I
> > figured the PE and the oil should have a K of around 2 at least ?
> > 3.) Why did the cap value drop as I removed the air ?
> > 4.) Why didnīt the cap change itīs value (not much at least) after
> standing a
> > few days?
> >
> > Please help a poor coiler who is scratching his head in vain, chewing
on his
> > finger nails trying to figure out what he did wrong.
> >
> > BTW:
> > 1.) I calcīd this value on my homebrew tc prog, but other progs gave me
the
> > same values, so it shouldnīt be a program bug.
> > 2.) Yes, the vacuum pump really did pump out air. This was clearly
> visible in
> > the glass jar where the oil foamed and bubbled as air was being removed
from
> > the PP container.
> > 3.) No, the PP container does not have an air leak. I greased the o-rings
> > thoroughly before assembly. During the vacuum run I put a thin film of oil
> > along the port and both end caps. No oil was sucked in and I didnīt
hear any
> > air being pulled in. So I figure it was vacuum tight.
> >
> > coiler greets from germany,
> > Reinhard
>
> --
> --Mr. Postman (Doug Brunner)
> <dabrunner-at-earthlink-dot-net>