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Re: Capacitor charge, were is it?



Tesla List wrote:
> 
> >> >> Subject: Re: Capacitor charge, were is it?
> >> Subject: Re: Capacitor charge, were is it?
> >> >> Subject: Re: Capacitor charge, were is it?
> >Subject: Re: Capacitor charge, were is it?
> 
> >From pgantt-at-ix-dot-netcom-dot-comSun Nov  3 22:50:49 1996
> Date: Sun, 3 Nov 1996 16:49:14 -0800
> From: pgantt-at-ix-dot-netcom-dot-com
> To: tesla-at-poodle.pupman-dot-com
> Subject: Re: Capacitor charge, were is it?
> 
> On 11/01/96 22:26:10 you wrote:
> >
> >> >> Subject: Re: Capacitor charge, were is it?
> >> Subject: Re: Capacitor charge, were is it?
> >> >> Subject: Re: Capacitor charge, were is it?
> >
> >>From hullr-at-whitlock-dot-comFri Nov  1 21:49:04 1996
> >Date: Fri, 01 Nov 1996 11:18:45 -0800
> >From: Richard Hull <hullr-at-whitlock-dot-com>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Capacitor charge, were is it?
> >
> >Tesla List wrote:
> >>
> <SNIP>
> >
> >
> >Water caps would be great for Tesla coils, but for the fact that it is so
> >terribly ionic in nature.  The plates would have to be metal or something
> >highly conductive.  Even with specially treated water, it would
> >immediately leach ions from the surface of the conducting plates and
> >quickly lose its dielctric properties and drift towards being a nice
> >conductor itself!
> >
> >I rely of triple distilled water for my dielectric water explosion
> >research.  Once the water is introduced into the accelerator/gun I must
> >fire quickly or the reaction is spoiled due to ionic cunduction.
> >
> >Richad Hull, TCBOR
> >
> >
> 
> Wouldn't it be possible to insulate the conductors in a water filled
> capacitor to prevent ionic migration into the H2O?
> 
> Phil Gantt (pgantt-at-ix-dot-netcom-dot-com)
> http://www-dot-netcom-dot-com/~pgantt/intro.html

Phil, 

There are a number of practical problems which, when combined, make a
water capacitor fairly impractical for coiling.

1. Ion leaching from other materials (including plastics):
Ions tend to leach from man plastics and other dielectric materials as
well. However, one could contiuously circulate the water through a
deionizing system to control this. 

2. Dielectric stress on the lower dielectric-constant material:
This one's a little tougher, but may be manageable. During rapid
charging/discharging, the voltage stress will be significantly greater
on the material having the lower dielectric constant. However, this
could be dealt with by matching the right thicknesses of water and
insulating material around the plates. For example, if the k for water
was 80, and the k for the insulating material was 2, then a water layer
of 80 mils would need to be matched up with an ion-barrier insulating
layer of 2 mils in order for the voltage distributions to be equivalent.
Non-equal distributions can also be employed as long as we never exceed
the breakdown strength of the barrier layer.

3. Leakage resistance matching:
This is a little more difficult to manage. Under steady state
conditions, the voltage distribution across the composite dielectric
will be distributed according to the leakage resistance of each section.
Although deionized water has fairly low conductivity, its still many
orders of magnitude greater than common plastics. This means that the
steady state voltage stress occur almost entirely across the barrier
layers, not the water layer. We could use doped plastics which have
higher conductivity, but this may just worsen our leaching problem, and
worsen's the Q of the capacitor.

4. "Treeing":
Many common plastics simply do not survive long under electrical stress
in the presence of liquid water. Over time, defects begin to grow,
forming dentritic structures (trees) which eventually short out the
dielectric barrier. This is a common failure mode, for example, in
buried polyethylene insulated high voltage cables. 


Safe coilin' to ya!

-- Bert --