Richard Goodwin wrote:
> For what voltage? The rate is proportional to the voltage.
When I start a batch, I crank it up to 2000 v. Then as I limit the
current to below 50 ma, the voltage drops down to maybe 500 or less.
Depends on spacing of the wires and immersion depth. Eventually I
will make this more standardized, but for now I'm stuck with a lot of
manual procedures.
Do you have any kind of graph of switch speed vs voltage?
I don't have a graph, I really don't have enough data points to make a
graph. I think you are making it a lot more difficult than need be. If
you use a simply current controlled supply with about 35 volts source
voltage ( which can be made using one resistor and a 7805 regulator) and
either spike the stuff to start with, or even better flow the water
through the cell, it is very easy to make consistant high quality and
high quantity EIS.
If not I'll approximate it from your earlier numbers, which I believe
were: 60 hz at 10,000 volts, and 1/2 cycle per minute for 20-30 volt
gradient.
Yes, those are the two data points.
What I really want to do is get or make a computer controlled power
supply. I would want to be able to write a program to control the
entire process: initial voltage and current based on electrode
surface area and distance, switching time, and shutoff time.
You cannot just have a shutoff time, as the progress will depending very
much on the quality of the water. Now if you spike it to a known
starting impedance then it might work.
Seems like you should be able to calculate ppm according to the
voltage and current and electrode geometry. Is there a formula for
this? You could just take a series of measurements with a ppm meter
and calibrate the system manually, I suppose.
You can compute the amount of silver from the current and time, minus
any which gets deposited on the other electrode. The formula has been
posted here many times, I am sure someone else has it handy
The big thing is the computer controlled power supply. So far I
haven't found one for any kind of reasonable price.
Get an wall wart which puts out 30 to 40 volts, put a constant current
diode in series with it, put a timer relay after that set to switch
every 60 seconds, and get a magnetic pump and a flow meter and flow the
water through the jug at a constant rate ( approximately 20 gallons per
hour per amp for 10-12 ppm EIS). Make sure you have enough anode to keep
it under 1 mA per square inch of active area. Monitor the ppm by the
voltage the current gives, and adjust the flow rate for the desired
ppm. Very easy, reliable, fast and consistent.
Marshall
Dick
------------------------------------------------------------------------
*From:* Marshall Dudley <[email protected]>
*To:* [email protected]
*Sent:* Mon, December 14, 2009 1:41:59 PM
*Subject:* Re: CS>Re: ac or dc?
Richard Goodwin wrote:
> I was thinking high voltage AC, like 10-15 kv.
> Perhaps the 60 hz ac doesn't work well because it switch so fast, it
doesn't give the silver particles time to separate far enough from
their electrodes, and they plate right back onto them in the reverse
cycle?
Yes that is the reason unless the voltages are high enough to get them
away from the layer which basically does not move with convection.
>
> If that is the case, then better stirring, or flowing of the water
might help.
It helps if the frequency is not too high for the voltage. But it does
little if the ions don't have time to move out of the layer of water
next to the electrode which hardly moves with stirring.
> I haven't tried ac yet, but will as soon as I can get a
transformer. I keep missing them on ebay. :-)
>
Go to a sign company that does neon signs. They replace signs and
usually have a bunch of old used transformers that they will give you
for free. 15,000 is best, but 12,000 will work. Remember that these
transformers name plate voltage is around 50% over the full load voltage.
> I use DC now -- high voltage to start a fresh batch, and gradually
lower it to limit the current. Electrophoresis power supplies are
readily available on ebay. Switching polarity makes them work much
better. So one question would be: what is the optimum switching rate?
For what voltage? The rate is proportional to the voltage.
Marshall
>
> Dick
>
> ------------------------------------------------------------------------
> *From:* Alchemysa <[email protected]
<mailto:[email protected]>>
> *To:* [email protected] <mailto:[email protected]>
> *Sent:* Fri, December 11, 2009 6:48:52 PM
> *Subject:* CS>Re: ac or dc?
>
> Genuine low voltage AC doesn't work at all. (i.e. a low voltage
50/60hz. AC wall adaptor). There a few low voltage AC adaptors around
so don't mistakenly try to use one.
>
> It has to be DC (or DC with polarity swapping).
>
> David
>
>
> >
> > From: Richard Goodwin <[email protected]
<mailto:[email protected]> <mailto:[email protected]
<mailto:[email protected]>>>
> > Date: 12 December 2009 4:49:46 AM
> > To: [email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>
> > Subject: CS>ac or dc?
> >
> >
> > Which do you think works better for making EIS, DC that you have
to switch polarity on every minute or so, or AC, assuming everything
else is equal?
> >
> > Dick
>
>
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