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RE: Plastic Pop Bottle SW Caps
From: "Payne, Will E" <will.e.payne-at-lmco-dot-com>
Thanks Jim ! Like my friend Kip, you like to brainstorm outside the
envelope. A fine habit !
Let me clarify one item, the aluminum foil was REPLACED by liquid
electrolyte, I did not use liquid and aluminum together. The next night I
graduated to a SS tub with a plastic grid in the bottom.
Your idea about copper sulfate is well taken, I will immediately search for
a cheap source. Theres a story behind this cheapskate approach to Tesla
Coils and SW capacitors. The illustrious Kip locally popularized the Hawg
Fence Antenna, a 1250 MHz antenna with 11 dB gain which costs $3 to make.
It is made from hardware cloth, or here in Georgia, "Hawg Fence Wire". The
idea was picked up by myself and others, and a series of "Hawg" project
seminars followed, where we would teach folks how to home grow some Hi Tek
Gadget real cheep -n- easy.
My current T Coil investigation are in the Hawg spirit and philosophy, which
is certainly NOT to rule out exotic solutions, only expensive ones ! One
fellow suggested I use heavy plastic bags for a dielectric, and I have
considered plastic pipe as well. Perhaps its time to present the local
techno-nerds with a workshop on building the "Hawg Tesla Coil" a small but
effective coil a novice can build for $25. My original Tesla Coil cost
about that much (SW caps from beer bottles), and thats about what a Hawg
project kit ought to cost. So, we seek original and exotic ideas, but
mostly CHEAP ideas.
I dont know a lot about electrolyte conductivity, but ion mobility as well
as valence will be important. However I suspect in our case the major
portion of resistance is contact resistance. Your sodium idea sure invokes
some wild and hilarious mental images, Kip will love it, as he did some
nuclear physics with liquid lithium. Plus, sodium is intrinsically cheap.
Will
> ----------
> From: Tesla List[SMTP:tesla-at-pupman-dot-com]
> Sent: Wednesday, August 26, 1998 22:08
> To: tesla-at-pupman-dot-com
> Subject: Re: Plastic Pop Bottle SW Caps
>
> Date: Wed, 26 Aug 1998 18:48:19 -0700
> From: Jim Lux <James.P.Lux-at-jpl.nasa.gov>
>
> Tesla List wrote:
> >
> > Last night I did a few experiments with a soda pop bottle PSWC (Plastic
> Salt
> > Water Capacitor) . The wall of a 2l plastic coke bottle measured 0.010
> +-
> > 0.0005 inch wall thickness. With a foil wrapping the bottle had
> measured
> > 2.4 nF, I fully expected to get one or two nF more with electrolyte
> > replacing the outer foil, but to my surprise the capacitance increased
> to
> > 8.5 nF !! Mike you were right about my skill at the subtle art of
> > bottle-foiling !
> >
>
>
> I'll jump in here with some comments...
>
> I would think the whole idea of using salt water is that it provides the
> conductor, and that adding aluminum foil to the combination is only
> asking for trouble. Of course, aluminum foil in salt water is a recipe
> for corrosion in the first place, and the aluminum salts that would
> deposite out are probably a good insulators as well.
>
> The thing to do, then, would be to get a big metallic corrosion
> resistant tub, fill it with saturated salt solution (if you use a copper
> tub, use Copper Sulfate). Then put your bottles, half filled with more
> salt solution in to the tub, spaced appropriately (several inches, I
> should think) from the sides and bottom (ideally, use an insulating
> support on the top of the bottles (out of the liquid)) Then, drop your
> bare copper wire (assuming copper sulfate here) into the liquid inside
> the bottles, but not touching the plastic.
>
> The saturated salt solution provides a uniform contact over the entire
> area of the dielectric (without any field concentrations due to wrinkles
> in foil, sharp corners, etc.) Of course, I suspect that most bottles
> are hardly uniform in thickness, so the field will concentrate at the
> thin spots. Based on this, bottles designed to hold pressure would be
> best, since thickness nonuniformities would make them weaker for the
> same amount of material. (Time to go drink that case of Champagne, all
> in the name of Science, right)....
>
> And, of course, floating a layer of oil over the top of the liquid, both
> inside and out, would reduce corona discharge at the edges.
>
> I don't know about the relative conductivities of various salts. If I
> had to start, I would choose a salt that would have high solubility (so
> there are lots of ions in the solution) and would be chemically similar
> to the electrodes (so it doesn't electrolyze or electroplate). Copper
> sulfate is pretty soluble, and is copper compatible, but I don't know
> how it compares to sodium chloride or magnesium sulfate. I also don't
> know if choosing a salt that has di or trivalent ions (like Mg++ or
> Al+++) would improve the conductivity over a monovalent ion (like Na+).
> It might: you have to move half as many ions for the same number of
> coulombs. Toxicity might also be an issue. Sodium Chloride in water,
> while cheap and readily available, does electrolyze to Chlorine gas and
> Sodium Hydroxide (which can, in turn, be turned in to Sodium
> Hypochlorite: bleach, a process done on a gargantuan scale
> commercially).
>
> What about using an electrolyte that isn't a water solution. Perhaps it
> is a bit exotic, but sodium is a fairly good conductor, and melts at a
> fairly low temperature (97.5 C). Mercury is a good conductor, a liquid,
> but does have significant safety hazards. Gallium is being used as a
> mercury replacement, and melts at low temperatures (it'll melt in your
> hand). Some ionic salts melt at low temperatures, and might be decent
> conductors when molten.
>
> Be original, be exotic, be the first on your block (or in the world) to
> use a sodium/sulfur/ceramic capacitor at 300 degrees C.
>
> Faugh on those who would use centuries old technology like glass leyden
> jars or ordinary salt water.
>
> That is, unless you are building a historical replica, in which case the
> hand turned oak balls gilded with gold leaf, the gutta percha insulation
> (carefully cured over a fire in the Amazon jungle for the optimum carbon
> loading to minimize corona), the silk insulation overwrap, and so forth
> are absolutely necessary.
>
>