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Resistive Ballasts

Water Reactor Discussions

Original Q.  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?

Responses

  1. The copper will not plate on the cathode with AC because there is no cathode in AC as the polarity changes polarity. I have found 316 stainless works in most cases. Titanium works in all cases but costs more.  Robert   H Carbon, graphite will erode in contact with water , the higher the current the faster. A 10 meg resistor should be fairly low current so erosion would be slow. Spark plug connectors make good connectors on 1/4 in electrodes like out of "D" cell batt.  ---Robert h

  2. You should use pencil leads or carbon rods (if you have them) to make the > connections to the water. Will produce H2 and O2 while in use. ---Eric

  3. 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.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. "  ---Jim L.

  4. Hi, I don't think using any salts of any kind would be needed for the range of resistance you're looking for. Even with distilled water you may find the resistor will have to be rather lengthy.  ---Rick W.