The ability to do work is measured in the electrical equation of Watts (Voltage x Amperage = Watts ). It takes a certain amount of Voltage/Amperage, or Watts, to perform the work ( which can be translated to a bunch of various units of energy ) to do the work of pulling electrons across a distance, through a resistive conduit (the Silver nitrate solution, measured in Ohms ). So a higher Voltage will mean use less Amperage, and vis a versa. That is the relationship. Throw in the geometrics of an electrowinning cell, Anode/Cathode distance, and you will have to become an artist of electrowinning. The V/A relationship will vary with every leach solution, cell configuration, and even the the electrical supply source. There is no one size fits all. Knowledge of electricity is equally important as the chemistry. Sorry if this is confusing, just had a couple of good beers.