url: http://escribe.com/health/thesilverlist/m61919.html
Re: CS>SilverGen specs.
From: Jack Dayton
Date: Tue, 12 Aug 2003 11:36:52
> Trem 8/12/03 8:28 AM Wrote:
>> Thanks for your compliment. Sorry but the circuit doesn't measure
>> current. It regulates current and measures voltage drop across
>> the electrodes in the cell. I use no zener for comparing voltage.
>> I use a potentiometer to set the trip point and use an op amp to
>> operate a relay for shutdown.
> Now, I hope you all get that, there's going to be a test later.
> (Well, there goes my grades.)
> Jack
There's many different ways to do it.
Maybe this will help. (View in fixed width font.)
Cell |\ ------- \
----------|+\ | | \
Ref | \ | Relay | ^ \----- Vin
---- | \------| | |
| | / | | ------- To Cell
/ Vadj | / | |
\<-----|-/ -------
/ |/
\
|
|
---
-
When the cell voltage drops below Vadj, the op amp turns the relay
on or off, depending on how it is connected.
The relay contacts open and remove the voltage to the cell. The cell
voltage then drops to a low value and holds the op amp in the
shutdown state.
This is a simple approach and is used by other cs generators. A
series pass transistor or MOSFET can be used to replace the relay.
The circuit needs some kind of bypass to allow the process to start.
It could be a simple switch across the relay contacts, but it is
probably a bit more complicated to allow the circuit to sense the
initial conductance of the dw.
This approach works quite well for general use, but there are
several problems. One is the slope of the cell voltage changes very
slowly at the end of the process.
If the pot is adjusted for maximum ppm, it will be very close to the
trip point at the end of the brew time, and a small amount of noise
or a bit of vibration that causes waves in the solution can
terminate the process early. So the ppm may vary from one run to the
next. Probably not enough to notice, but it's part of the process
repeatability.
Another problem with using the cell voltage to terminate the process
is the sensitivity to the initial conductance of the dw. So the ppm
may change with different brands of dw.
A different approach can provide much better process repeatibility.
I recently posted information on a Cheap, High-Compliance Constant
Current Source
http://escribe.com/health/thesilverlist/m61896.html
This can set the cell current to the desired level regardless of
changes in conductance. Then you can use the Faraday equation to
determine the brew time, and turn the power off at the desired time.
If you have good quality dw and run at very low current density, you
can go well past the point where gray whiskers start forming on the
cathode. Even though some of the silver ions are diverted to making
sludge, the cell conductance continues to drop. This indicates some
ions are remaining in solution.
Then, if you use electrodes that have no sharp edges or bends, you
can make high ppm cs that won't turn yellow.
I did this with Godzilla. The electrodes are 48 inches of 12 ga
wound into a spiral. They sit horizontally in a Pyrex 2 litre
measuring cup.
There are no sharp bends anywhere to cause production of silver
oxide from the Ag(+) and OH(-) ions at the concentration points.
I had some problems with the hard black coat produced by the new
WallMart dw, but running a few batches with the Life dw eventually
cleaned both electrodes and they now run clean.
Now I can push the process well past the point where the solution in
my previous cs generator would simply turn yellow. The resulting cs
gives a very strong dispersion in the salt test, but remains crystal
clear with no sign of turning color.
So the moral of the story is to get rid of all the sharp edges and
run constant current if you want to make repeatable, high ppm cs!
Best Regards,
Mike Monett
P.S. Be on the lookout for viruses. I got another one from the list
today, but my spam program kicked it out as usual. They won't run
on my system, so I have no worries. But others may not be so lucky.
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