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Water HV divider (was RE: Water resistors electrodes)

Original poster: Marco.Denicolai-at-tellabs-dot-com 

Hi all,

Ok, I was cheating. Actually I want to build a water HV divider. The
basic principle can be found in my quick-and-dirty page:


Chek also the link in there for a commercial version of it.

Jim, you have got good hints on your water resistor page. I thought to
use copper because I want to use a copper valve and copper is easier to
solder than stainless steel :)

What about removing the air bubbles the same way than for old rolled
capacitors? I have got an old refrigerator compressor that I can use as
vacuum pump. Transformer oil foamed quite easily, what about water?

I plan to use a copper plate for top and another for bottom electrode.
On the outside two aluminium toroids. The bottom copper plate mount a
BNC connector, body to the bottom (GND) plate, conductor soldered to a
second copper plate (the grid) that, therefore, is some millimiters
spaced from the bottom electrode and works as the divider tap.
Capacitance, resistance and inductance ratios should be all
automatically balanced by the geometry -> reduced compensation problems.

The tube is made of plexiglass. On the top a brass hose barb or a copper
valve for filling and air removal. Thermal dilatation remains a

Ideas, suggestions?

Best Regards

 > -----Original Message-----
 > From: tesla-at-pupman-dot-com [mailto:tesla-at-pupman-dot-com]
 > Sent: 2. kesäkuuta 2004 20:56
 > To: tesla-at-pupman-dot-com
 > Subject: Re: Water resistors electrodes
 > Original poster: Jim Lux <jimlux-at-earthlink-dot-net>
 > At 08:00 AM 6/2/2004 -0600, you wrote:
 > >Original poster: Marco.Denicolai-at-tellabs-dot-com
 > >Hi all,
 > >
 > >This may be an old question but...
 > >
 > >I want to make a water resistor using copper sulphate solution and
 > >copper electrodes. In the range of 10 Mohms.
 > >Will material from the copper anode be transferred to the cathode and
 > >change the resistor characteristics?
 > >Will I get some precipitate (Cu) with AC or not?
 > >Is there a better material for the electrodes?
 > >
 > >Best Regards
 > Yes, some material will be transferred, but not a whole lot.  You can
 > calculate how much by figuring out how many coulombs (amps *
 > seconds) of
 > charge will transfer, then convert coulombs to moles  (about 1E5
 > coulombs/mol, as I recall). A mol of Cu is 63-64 grams
 > (probably about 10 cc?)
 > Since you're probably not running a continuous current of amps...
 > Say 1 mA (10kV across the resistor) for an hour (3600 sec)...
 > 3.6 coulombs
 > -> 2 mg of Cu (I might be off by a factor of 10, but it's a
 > small amount
 > either way)
 > The challenge is always sealing the electrodes to the tubing or pipe,
 > especially if you want a totally sealed resistor that is orientation
 > insensitive.  Copper works great. You can get copper hardware
 > at places
 > selling to the boating/marine market. Brass would probably
 > also work, and
 > is more available.
 > by the way, 10 Meg won't take much copper sulfate, or it will
 > take a long
 > skinny tube.
 > from http://home.earthlink-dot-net/~jimlux/hv/rwater.htm
 > "As a practical starting point for your calculations: A 1
 > meter length of
 > 1/4 inch id tubing filled with 0.1 Molar Copper Sulfate (1.6
 > g in 100 cc
 > water) has a measured resistance of 39.8 Kohms. "