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Re: Glass/poly and more...
From: Phil Chalk[SMTP:philoc-at-ozemail-dot-com.au]
Sent: Thursday, September 18, 1997 5:53 PM
To: Tesla List
Subject: Re: Glass/poly and more...
Tesla List wrote:
> >
> >Hmmmm.....
> >
> >> From: Daryl P. Dacko[SMTP:mycrump-at-cris-dot-com]
> >> Sent: Tuesday, September 16, 1997 6:35 AM
> >> To: Tesla List
> >> Subject: Re: Glass/poly and more...
> >>
> >> At 05:30 PM 9/15/97 -0500, you wrote:
> >> >
> >> >A while back , perhaps 5 moths ago, I made a saline cap from
> >> >a very tall cylindrical wine bottle (Rene' Junot). The ouside was
> >> >wraped in aluminum foil, water sofner salt was poured in to the
> >> >shoulder level, then water water added to cover, motor oil filled
>
> >> >the remaining space as a sealant.
>
> <snip>
>
> >> >Next step was AC seasoning with about 5KV for a few hours at a
> time.
> >> >Shortly after it's construction and preping, it measured 680 pf.
> >> >I must mention that was never used in TC service, but sat on the
> basement
> >> >floor for those 5 months. Now it reads 1200 pf.
> >> >Guess using a wine bottle makes it get better with age. (I'm
> joking)
> >> >
> >> >Maybe the copper reacting with the salt is making copper cloride
> which
> >> >lowers the internal resistance and thus the impedance seen by the
> bridge?
> >> >
> >> >I know you were looking for oil cap experiences, but I thought I'd
> throw
> >> >this
> >> >little experience in the ring anyway.
> >> >
> >> >Jim M
> >>
> >> An interesting hypothsis follows:
> >>
> >> Glass will absorb water, forming a hydrated layer that increases
> with depth
> >> the longer it sits.
> >>
> >> Water has a very high (I'm on vacation and lost without my books)
> dieletric
> >> constant.
> >>
> >> It would make sense to me that if glass sat in contact with water,
> it would
> >> make a better cap due to it's dieletric constant increase.
> >>
> >> Q.E.D
> >>
> >> Daryl
> >
> >Unfortunately, water dissolves glass slowly which increases the ionic
>
> >content of the water and makes a less than suitable dielectric.
> >
> >QED
> >Malcolm
>
> Yep, it does dissolve in water slowly - makeing a bad cap into an even
> worse
> one as the lossy effects of a higher dieletric constant make itself
> known ;'}
>
> I seem to remember that the sodium, potassium and calcium (etc, etc.)
> dissolve much faster than the silicon, and this in turn forms an open
> lattice holding water and water bound into a 'jelly'.
>
> I suppose it could be a surface area effect too, since most stuff in
> the world
> has more than one cause and effect vector...
>
> I suppose that I should make up a salt water cap and measure it's
> value
> and dissipation factor over a few months, now that my interest is up.
>
> I hope never to go back to salt water caps, but you never know ;'}
>
> Daryl
Hi all,
I'm diving in here because this thread has been going for a while, & It
seems to me like people are barking up the wrong tree.
I can't explain the capacitance increase, but it seems to me that the
characteristics of the salt solution should not effect the capacitance
much. 'Glass ions' absorbed into the water shouldn't matter much,
though the mechanism of this last post, with water molecules integrating
themselves into the glass lattice, maybe closer to it.
_Distilled_ water is quoted as K~80. Distilled water is considered an
electrical insulator till it breaks down. Water full of ions is not a
good insulator, therefore not a good dielectric material anyway, & sure
to have a different (lower) value of K. (P.S. What is the dielectric
constant of, say, copper or carbon ? - are these sensible questions ?)
The function of the water in these caps is to i) provide a large
surface area in intimate contact with the inside of the bottle - forming
one 'plate' & ii) to electrically connect the 'plate', so formed, to
the terminal wire in the bottle neck. For these reasons the fluid must
be conductive.
If you wish to consider the water as dielectric, then you have one foil
'plate' on the outside of the bottle; a large thickness of (glass+water)
as dielectric; and your bottle-top terminal wire (i.e. v. little surface
_area_) as the other plate. This would yield a very low capacitance,
with a very lossy (partly conductive) dielectric.
If you start with a saturated salt solution, or close to it, any
contribution to the ionic content from the glass, even over 5mths, is
likely to be negligible. If however it does increase the conductivity
of the solution, that would appear equivalent to reducing the internal
series resistance of the cap ( e.g. you may now have 1200pF in series
with 20R, previously was 1200pF in series with 100R, or whatever the
numbers are) & this may be reflected in the reading on your meter. How
did you measure C ? When I first made a TC cap, & didn't then have a C
meter, I put the C in series with variable R across 240Vac mains, as
voltage divider, calculate XC from voltage readings & calculate C from
XC at 50 Hz. If you're using a multimeter with Cmeter, it probably
subjects cap to a couple of volts at 1kHz (wild guess) & I'd be
interested to obtain values by other methods, for comparison.
Okay, so am I the idiot here ????
Regards,
Phil Chalk.