Author Topic: Why cell voltage above 10 volts?  (Read 227 times)

Offline axkman

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Why cell voltage above 10 volts?
« on: August 22, 2020, 06:19:03 PM »
Hi there!

I read here on the forum that it was advised to keep the cell voltage above 10 volts, but my question: why does the cell voltage needs to be above 10 volts?

Thank you!
« Last Edit: August 22, 2020, 08:54:42 PM by axkman »

Offline Gene

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Re: Why cell voltage above 10 volts?
« Reply #1 on: August 23, 2020, 02:33:41 AM »
You're running an electroplating cell thats designed to fail for using the electrolyte we use.

In a functioning plating cell the silver ions would be pulled into solution and then deposited on the cathode (a.k.a. plating). The electrolyte we use inhibits this plating action from happening but it serves a couple other purposes - reducing the resistance of water which is nearly a perfect insulator so you can get milliamps of current through it and raising the PH to around 8-8.5 so that the reducer works as they only reduce in alkaline environments.

There's chemistry involved, zeta potential,... as to why you want 10V minimum. A little higher (I usually process around 12V) is even better.  Higher is even better.

As I recall, this was a question that was answered on the forum in the past though the search facility being as stellar as it is, good luck finding it.

Offline axkman

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Re: Why cell voltage above 10 volts?
« Reply #2 on: August 23, 2020, 12:01:20 PM »
Thank you for your reply. Hugely appreciated, as always.

I'm browsing thru the search engine. There is a lot of search results as to 10v cell voltage and that some people wrote "kephra said so" (and I know he knows what he's doing!) but haven't found a conclusive post why the cell voltage needs to be at 10v.
Electrodissolution (process of the silver being pulled away from anode into solution) happens at lower voltage than 10v aswell. And the rate of silver ions pulled away from anode into solution is depending on the current that flows from one electrode to the other thru the (distilled water + electrolyte) solution. So I still kind of wonder why that is said need to be at cell voltage of 10v or higher.


Offline Gene

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Re: Why cell voltage above 10 volts?
« Reply #3 on: August 23, 2020, 07:58:06 PM »
Here's Kephra's explanation.

Its a good read but his take on the voltage thing is in the Electrolyte section of his post.

https://www.cgcsforum.org/index.php?topic=1143.msg8849#msg8849


Offline axkman

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Re: Why cell voltage above 10 volts?
« Reply #4 on: August 23, 2020, 11:47:38 PM »
Thanks man!

Nicely detailed explained, appreciated!

Offline ESTACIONSJ

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Re: Why cell voltage above 10 volts?
« Reply #5 on: September 30, 2020, 04:41:09 AM »
so i have a question, so i have a power supply that has a constant current setting, so if i set my constant current at  say 12 volts and the amps at 15ma because im using a silver 1oz bar i should be good...

Offline cfnisbet

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Re: Why cell voltage above 10 volts?
« Reply #6 on: September 30, 2020, 09:01:16 AM »
so i have a question, so i have a power supply that has a constant current setting, so if i set my constant current at  say 12 volts and the amps at 15ma because im using a silver 1oz bar i should be good...
No, you can't do that. You can only set the current or the voltage to be constant. In your case, you would set the constant current to be 15mA and allow the voltage to drift. Then you adjust the amount of cathode in the water (minimise it) to keep the voltage above 10 volts (ideally higher).

"constant current at  say 12 volts" - is incorrect; volts is voltage, so that would be constant voltage, which you don't want to do.

Offline ESTACIONSJ

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Re: Why cell voltage above 10 volts?
« Reply #7 on: September 30, 2020, 11:43:10 PM »
okay thank u for the info, if u say to keep the voltage above 10 volts (ideally higher). whats the highest Volts u would want it to be.

Offline Gene

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Re: Why cell voltage above 10 volts?
« Reply #8 on: October 01, 2020, 02:54:41 AM »
Higher is better BUT given the resistivity of your cell due to the electrolyte, you're going to get to a point where you can't go any higher because the cathode has come out of the water. There are limits.  You're just going to have to play around to see what those limits are at 15ma.

The thing is though, you don't want the cathode so close to being out of the water that evaporation or a little mechanical vibration disconnects it from the cell because then you'll have absolutely no idea what you actually made as far as PPM.

We use a thin 24 AWG (american wire gage which is a standard) length of copper wire.  The trick with the cathode is to minimize the surface area in the water.  For a thick wire, that means just glancing the surface which isn't such a good idea.  For a thin wire like this, for sure you'll still have a good half inch in the water when you're up around or over 12V. 12-15V is good. You don't really have to try to get any higher.  If you're stirring though you may be able to because stirring causes the electrical path from the anode to cathode through the water to get longer (an arc is longer than a straight line, right?) but don't push it too far.  If its good enough, its good enough!  Words to live by. "Perfection" is not required - just good enough (wink).

As far as the power supply, does it have constant current and constant voltage settings? If so, I'd doubt you can use both at the same time.  If its a current "limiter", thats different.  Thats usually there for protection so if whatever you're powering shorts out, your power supply doesn't smoke or die.

What you want to do is set the voltage high (say 20+V if you can) and adjust the current limit just measuring the current across the supply with a voltmeter to get 15ma.  BIG WARNING. For a power supply, I'm sure the current limit can be set to several amps at least.  TURN THE CURRENT LIMIT TO ITS MINIMUM SETTING (lowest current) setting BEFORE connecting the voltmeter or you may well blow it out.  Then gently adjust it to get where you want. Given your cell will be 12-15V, if the supply is outputting 20-24V, there's no way, unless the cathode comes out of the water, that the current won't remain constant at 15ma.

Let us know how you make out.

Oh, and if you manage to damage your voltmeter on a current scale, don't toss it. They ALL have an internal fuse or two you can replace and chances are good you sent it to that big fuse round-up in the sky. Some meters even have a spare fuse hidden inside but usually these are the more expensive ones. Just get a replacement fuse with the exact same rating and you're good.

Offline ESTACIONSJ

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Re: Why cell voltage above 10 volts?
« Reply #9 on: October 01, 2020, 05:49:09 AM »
thanks for the advice, made my first batch quick in 50 minutes. With my new set up and ure guys advice
here are some pictures.

1 litres DW x 50 ppm x 15   =   50 minutes   
                  15 mA

20 drops of electrolyte and 20 drops of reducer (karo syrup mix), then silver cleaned after with butane torch

thanks for the advice, made my first batch quick in 50 minutes. With my new set up and ure guys advice
here are some pictures.




<img src="https://i.imgur.com/tFKhUoq.jpg" title="source: imgur.com" />
« Last Edit: October 01, 2020, 06:00:21 AM by ESTACIONSJ »

Offline cfnisbet

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Re: Why cell voltage above 10 volts?
« Reply #10 on: October 01, 2020, 07:17:37 PM »
Looks excellent!

Offline Gene

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Re: Why cell voltage above 10 volts?
« Reply #11 on: October 01, 2020, 08:56:17 PM »
I agree.  It looks great - just the right color for 50PPM.

When you get up around 80PPM+ it starts looking a little more red (don't worry - dilute a little to 20PPM and if its the right color, you're good) and when you start getting up around 120PPM, it starts looking a more reddish/brown (more reddish than brown) just due to the concentration of silver particles in the water.

Also, other than lab borosilicate glassware, all soda glass (which is what most glass containers are) has a little color to it.  Sometimes holding it up to light you can see it, especially with thicker walled containers like mason jars.  I even have one that looks a little yellow.  So this can affect the actual color you see.  Not by a huge amount but it does a little.  Just saying.

If you choose to gel cap, it will get a bit darker even.

If you choose to reduce with maltodextrin, it will get a bit darker than with Karo.

I wouldn't suggest reducing with Karo for anything over 20PPM (its not a great stabilizer).  It'll keep for a while but I would want to use it up in the first 3-6 months. You're better off using maltodextrin or even better, just gel cap it.

If you gel cap, it will keep for a VERY long time.  I've had some for 3-4 years that was still every bit as good as the day I made it.

Though it won't hurt anything, you're a bit high on the reducer.  The equation to calculate how many drops of 50/50 diluted Karo you need is as follows:

PPM * DW(milliliters) / 16000

So, 50 * 1000 / 16000 = 3.125 drops

Yup, you don't need much. I'd recommend adding 3-4 extra drops for any calculated amount as more reducer causes faster reduction but you don't need to go overboard.

Offline ESTACIONSJ

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Re: Why cell voltage above 10 volts?
« Reply #12 on: October 01, 2020, 10:29:00 PM »
thanks for the reducer calculation, that will come in handy , so if i try 80 ppm at 1liter just need 5 drops.
Thanks for all the help

Offline Gene

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Re: Why cell voltage above 10 volts?
« Reply #13 on: October 02, 2020, 06:39:48 AM »
Yes, 5 drops.

I'd highly suggest you add a bit more - say 2-3 extra drops.  The reason being is that no measurement is completely accurate and with "drops" for sure 20 drops equals really close to 1ml but nothing is perfect.  And then too, your time measurement isn't perfect nor your current measurement either so a little extra covers your arse for all the minor issues that can arise that could push the PPM a bit higher than you wanted.  Also, a bit more reducer helps to speed up reduction a little.

At 15ma, in 1 liter, you're building 1PPM per minute.  If you miss by a few minutes (over), as you can see, you're covered with that 2-3 drops extra you added.

Like I said, A little extra is good.  More won't hurt but why overdo it? Right?