I just finished making up a circuit based on Mike Monett's schematic for a simple auto shutoff
circuit for a colloidal silver generator. (Thanks Mike!) From:
http://silversol.freewebpage.org/systems/csoff.htm
His auto shutoff circuit was calculated out for 5 volt operation. I wanted to set it up for 24 volt
since I had a 24 volt relay and wanted to use a 47K ohm potentiometer and a 40 volt power supply
cube I took from an old printer that was being scrapped out.
I tried to run his formulas on the Mercury program, but either they were incorrect or I entered them
incorrectly since the circuit didn't work properly. Not being an engineer, I used my technician
sense and got it working. I provided a simple 24 volt regulated supply and an adjustable current
source using LM317 ICs. Values for components are as follows:
R1 = 150K ohms
R2 = 150K ohms
R3 = 39K ohms
R4 = 47K ohms
R5 = 10K ohms
R6 = 12K ohms
C2 = .1uf
U1 = LM324A
I don't suggest that these values are optimum, just that they worked well for
me...
I stuck an LED in the lead going to the current generator so that when the relay closes and current
starts through the cell I have an indicator which shows that. No need for a resistor.
I also stuck some banana jacks in series with the cell for the current meter.
I set the current regulator to 20ma since I have a 3" X 6" piece of silver for the anode (+) and two
1.5" X 6" copper cathodes (-), one on each side of the anode, so I am using both sides of the anode
(for 33 square inches of wetted anode area). The current regulator is run off the 40 Volt supply.
The maximum cell threshold for shutoff tests out to 27.5 Volts and
the minimum cell threshold for shutoff tests out to 5.0 Volts.
This gives a wide cell resistance shutoff range.
I'm confusing myself a bit thinking about this since the voltages and resistances involved would
change with different electrode size and spacing and the setting of the current source value. At
any rate, looking back on my notes, the cell I was using with the 1ma current limit and the 8" long
12 gage electrodes with approx 2 sq in wetted area and 1.25 inch spacing shut off at about 5 Volts.
The current cell described first above is shut off at 14 Volts.
Anyway, using the Excel program Faraday Calculator and the currents I recorded every 15 minutes, I
stopped the process when Faraday calculator indicated 23ppm and there was some grey-beard showing up
on the edges of the cathode. Reads 19.5 uS (NaCl). Used Ode's magnetic stirrer with the large
plastic tube on it. The entire time for the batch (sun tea jar, 1 gallon + 1.5 cups, 4140ml) took
1.75 hours. The CS looks nice and clear.
Boy, that works slick!
Dan
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