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Old 08-10-2017, 12:22   #1
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Home made silver/silver chloride half cell

silver/silver chloride electrode - anyone actually made one?

The cunning plan is......
Onboard my steel boat there already is a calibrated silver/silver chloride reference electrode which gets dug out now and again.
What would be nice would be to make something which could get dropped over the side once the anchor is dug in attached to a raspberry pi monitoring/logging accurate voltage, I wouldn't like to leave the expensive one in the water for a long time though could be used to check the home made one.

So , some stuff on the web varying from science lab to a bit of silver wire.

Just wondering if anyone has tried similar with any success / tips?

https://www.tau.ac.il/~advanal/ReferenceElectrode.htm
Chloriding a silver wire -- making a silver chloride electrode - VHLab Wiki
https://publiclab.org/notes/JSummers...ost-electrodes
Silver/silver chloride reference electrode
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Old 08-10-2017, 16:08   #2
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Re: Home made silver/silver chloride half cell

I just use a silver electrode. It's only 0.1 volt different from a silver half cell.

Gord posted an extensive list on a different thread involving metals and their respective voltages.
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Old 08-10-2017, 16:34   #3
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Re: Home made silver/silver chloride half cell

Quote:
Originally Posted by senormechanico View Post
I just use a silver electrode. It's only 0.1 volt different from a silver half cell.

Gord posted an extensive list on a different thread involving metals and their respective voltages.
That's quite a lot on the galvanic series - is that measured against a calibrated electrode from a table?

Suppose if the voltage from just silver was reliable you could make up a conversion factor.
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Old 08-10-2017, 17:19   #4
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Re: Home made silver/silver chloride half cell

I'll try to find it.
If Gord sees this thread, I'll bet he'll repost it.

Yes, I allowed for the difference in voltage when I calibrated my homemade zinc saver circuit.
It is an impressed voltage system using an IC, an op amp, and a FET transistor.
The whole thing draws 0.020 amps from the boat's battery bank.
It's adjustable, which automatically impresses just enough voltage and current to protect the boat's bonding system.

I posted the schematic here several years ago.

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Old 08-10-2017, 18:44   #5
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Re: Home made silver/silver chloride half cell

Quote:
Originally Posted by conachair View Post
silver/silver chloride electrode - anyone actually made one?

The cunning plan is......
Onboard my steel boat there already is a calibrated silver/silver chloride reference electrode which gets dug out now and again.
What would be nice would be to make something which could get dropped over the side once the anchor is dug in attached to a raspberry pi monitoring/logging accurate voltage, I wouldn't like to leave the expensive one in the water for a long time though could be used to check the home made one.

So , some stuff on the web varying from science lab to a bit of silver wire.

Just wondering if anyone has tried similar with any success / tips?

https://www.tau.ac.il/~advanal/ReferenceElectrode.htm
Chloriding a silver wire -- making a silver chloride electrode - VHLab Wiki
https://publiclab.org/notes/JSummers...ost-electrodes
Silver/silver chloride reference electrode
I think that to monitor your boats Cathodic Protection system is an excellent idea. I have been monitoring CP systems on ships and oil production platforms etc using a trusty Ag/AgCl reference electrode since the early 1980,s. Manufactured a few tonnes of sacrificial anodes since then as well. We now supply a small "consumer" monitoring Ref electrode kit, principally to monitor Saildrive Leg protection but applicable to any small sacrificial anode application.
So yes there are a few tricks and tips for Reference electrode chlorination but thats what you pay for when purchasing.
PM me if you are interested in purchasing a kit.
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Old 09-10-2017, 01:19   #6
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Re: Home made silver/silver chloride half cell

Quote:
Originally Posted by senormechanico View Post
I'll try to find it.
If Gord sees this thread, I'll bet he'll repost it.

Yes, I allowed for the difference in voltage when I calibrated my homemade zinc saver circuit.
It is an impressed voltage system using an IC, an op amp, and a FET transistor.
The whole thing draws 0.020 amps from the boat's battery bank.
It's adjustable, which automatically impresses just enough voltage and current to protect the boat's bonding system.

I posted the schematic here several years ago.
Thanks, much to think about. Maybe it's worth building a similar circuit as I'm onboard all the time to keep an eye on things. I've found some of your other posts and the allaboutcircuits thread. I got lifted out last week to find something has zapped my anodes in the last year and I've no idea where or how, usually there isn't that much wear - steel 33" Ebbtide.

So from the searches - did you just use an old silver coin as an electrode?

Initial thoughts were to get some silver wire off ebay, maybe a coin or something would work just as well though google searches suggested making Ag/AgCl isn't that hard - immerse the silver in bleach for a while.

Lots to learn - thanks for pointing me down the road
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Old 09-10-2017, 01:21   #7
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Re: Home made silver/silver chloride half cell

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Originally Posted by frant View Post
So yes there are a few tricks and tips for Reference electrode chlorination but thats what you pay for when purchasing.
PM me if you are interested in purchasing a kit.
Thanks, I have a commercial half cell already but don't want to leave it in the water full time so looking at making something and keep the bought half cell for checking calibration. Rather than purchasing more.
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Old 09-10-2017, 03:47   #8
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Re: Home made silver/silver chloride half cell

Also, Senormechanico - did you by any chance look into impressed current systems at all?
Looking at your circuit - looks like you can "turn down" the zinc anode and reduce the voltage difference between the hull and reference electrode but not add more if there isn't enough zinc left.
Impressed current looks interesting with just a little peep into google, maybe too fraught with danger if you get it wrong so in the real world a big lump of zinc and circuit like yours might make more sense on a small boat. Especially if learning along the way..
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Old 09-10-2017, 11:00   #9
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Re: Home made silver/silver chloride half cell

The circuit is basically a "volume control" for the zinc.
With one big zinc and a direct connection to the bonding system, it would supply -1.0 volts.
That's too much, and burned spots around the thru hulls is the result.
That is why I built the circuit with help from the allaboutcircuits guys.
The variable potentiometer in the circuit sets the bonding system voltage setting.
The current supplied by the zinc will vary depending on the salinity, but the voltage is constant due to the sampling of the circuit.
I have no paint burn, the zinc lasts for easily 2-3 years, and no metal damages, prop included.
I check the voltage with a multimeter every 6 months or so. Rock solid.
Using a 90% silver dime vs a .999% silver electrode I found the voltage difference to be about 0.05 between the two.
The difference between a silver chloride half cell and a .999 silver electrode is 0.1v, so I just upped the (usually recommended -.0.550) voltage adjustment by 0.15 volts @ -0.650v.
(Measured between the dime and bonding system)

I saw an impressed voltage system for sale at the boat show. $1,000 USD !
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Old 09-10-2017, 11:56   #10
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Re: Home made silver/silver chloride half cell

Thanks for the reply. I will definitely come up with something. The rate of advance of microprocessors available cheaply is quite something these past not so many years. Something like an esp8266 or esp32 could do the work of voltage monitoring and controlling a FET for milliamps draw and a few dollars plus send it all over wifi to my existing raspberry pi for logging and alarms. First thing will be to get the hold of some silver from somewhere and make a start.
I've had paint blown off by too much zinc on my steel boat before as well, took a bit of research to track it down!
One more question, where do you have the silver electrode mounted? Most of my time is spent anchored so I'm thinking the most practical way would be drop the hook then a zinc over the side from the cockpit but not so sure where the best place would be for the silver, does it need to be some distance away from the zinc?

Thanks again
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Old 09-10-2017, 12:32   #11
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Re: Home made silver/silver chloride half cell

My current boat, steel construction, came with this system, if you aren't interested in re-inventing the wheel. Great system.

Capac-DS-0408.pdf
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Old 09-10-2017, 13:17   #12
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Re: Home made silver/silver chloride half cell

Quote:
Originally Posted by senormechanico View Post
I'll try to find it.
If Gord sees this thread, I'll bet he'll repost it.

Yes, I allowed for the difference in voltage when I calibrated my homemade zinc saver circuit.
It is an impressed voltage system using an IC, an op amp, and a FET transistor.
The whole thing draws 0.020 amps from the boat's battery bank.
It's adjustable, which automatically impresses just enough voltage and current to protect the boat's bonding system.

I posted the schematic here several years ago.

Not sure if I understand the theory here.
The sacrificial Zincs that are typically bonded to the steel hull are isolated from the hull and brought to the drain of a FET? When the FET is off, the reference electrode measures low voltage and the FET turns on. When the FET turns on the reference electrode measures a positive voltage with respect to the steel hull. If the pot is adjusted so that the voltage reference at the amplifier greater than the voltage sensed, the FET remains on for ever so there is no need for a circuit. Just bond the zincs to the hull. If the pot is adjusted so that the reference at the amplifier is less than the sensed voltage the FET turns off and the sensed voltage drops, which turns the FET back on, so it acts like an oscillator.
OK the schematic is blurry and my eyes are not what they used to be so what I thought I saw may not be the actual circuit, if so please send a higher res schematic. Thank you.
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Old 09-10-2017, 14:43   #13
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Re: Home made silver/silver chloride half cell

The zinc is on a GRP hull, also insulated by a thin vinyl sheet.
The circuit is indeed an oscillator. It checks the differential approximately every 45 seconds.
I know this because I can hear a short "brrrp" in my HAM radio when it checks (and adjusts if necessary) the voltage differential.

To raise the protection voltage range, I changed R2 to a total of 16k.
I also added a .00f uF capacitor across the FET drain to source to cut down on RFI.
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Old 13-10-2017, 05:31   #14
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Re: Home made silver/silver chloride half cell

Quote:
Originally Posted by senormechanico View Post
The zinc is on a GRP hull, also insulated by a thin vinyl sheet.
The circuit is indeed an oscillator. It checks the differential approximately every 45 seconds.
I know this because I can hear a short "brrrp" in my HAM radio when it checks (and adjusts if necessary) the voltage differential.

To raise the protection voltage range, I changed R2 to a total of 16k.
I also added a .00f uF capacitor across the FET drain to source to cut down on RFI.
It is a very clever idea indeed to have a "volume control" and regulate the amount of cathodic protection at the optimum level thus minimize the erosion at the zinc anodes.
I had big plans to build a 75ft steel boat in retirement, had things worked out corrosion prevention would have been my top priority. Unfortunately when the numbers were added up, just the paint and hull maintenance for a 75ft steel boat blew my retirement budget.
Oh well, hello plastic.
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Old 06-12-2017, 22:02   #15
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Re: Home made silver/silver chloride half cell

Actually set the differential at -0.600 because the silver electrode (90% silver dime) is -0.130 volts whereas .999 silver is -0.100 volts.

My circuit is set with the .999 silver probe to read -0.600 volts.
It reads -0.570 volts using the silver dime.

Actual negative from bonding system to water is -0.700 volts.
Plenty of protection, no paint burn, no galvanic corrosion either.
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