Re: The manufacture of capacitors
In a message dated 96-12-10 17:24:31 EST, you write:
<< Why not go the whole way and eliminate the solid dielectric
material between the plates? >>
I contemplated this very project and did lots of research on the matter but
decided that in several ways the "physical" dielectric approach was better
for these reasons:
1) The dielectric strength of oil is much lower than that of
polyprop/polyethylene. For instance the dielectric strength of mineral based
oils is about 250v/mil ( about half what it is for the afore mentioned
plastics.) This would require twice the spacing between the plates as
compared with the plastics which then requires twice the number of plates to
regain the "lost" capacity as spacing increases.
2) All the extra spacing and plates results in a cap that is at least twice
the size and several times the weight (because of all the extra oil) of the
equivalent "plastic" variety.
3) The plates can no longer be made of aluminum foil or even flashing
because an operating capacitor in a TC circuit sees so much current/voltage
that a great deal of attractive and repulsive force is developed between
adjacent plates creating a vibrating accordion effect. Minimizing this
effect requires much thicker/stiffer/more expensive plate material (steel?)
and results in greatly increased fabrication problems since I don't have a
machine shop handy to cut and trim steel plate.
4) Somewhat greater dielectric strength of 350v/mil is possible if one uses
Silicone oil as the dielectric but at $6.00/lb or $48.00 per gallon (and one
would probably need a couple of gallons) the cost is simply too high.
5) So for cost, size, weight, and fabrication reasons, I abandoned the
approach. But if someone has the time, money, and shop to do it in Go To It!
And keep me informed on your progress.
6) P.S. I also found out ( after weeks of research) that "electrical grade"
Castor oil might actually be the ideal dielectric as it has twice the
dielectric constant of the other oils, a breakdown voltage 850v/mil and the
dissipation factor actually *falls* as operating frequency increases! I
would be very interested, perhaps, in working with someone in designing such
a cap. Any takers?