STRAY CURRENT Issues, need help!

[boatpoker]

Originally Posted by Fiso

Man, you guys have me baffled in your responses as they make no sense. The Anode (positively charged one) to the Cathode (negatively charged one) flows electrons from the positively ones to the negatively ones. If I charge an ION of a material to the positive charged state, it will flow, and bond, to the one with the positively the charged state. If I bombard and ion of (Name your material here) from the Anode to the Cathode, I deplete one while adding to the other. Name your metal here?

If you do that from a naturally occurring potential difference between the two or an induced potential between the two, what changed physically in that process except what we call it?

Do some more research ...
Galvanic corrosion - Anode negative, cathode positive.
Electrolysis - Anode positive, cathode negative ... an induced process as used in electroplating.
It took me years of education to understand this, you are not going to learn it on this forum.

I have nothing to add.

[Fiso]

Originally Posted by boatpoker

Do some more research ...
Galvanic corrosion - Anode negative, cathode positive.
Electrolysis - Anode positive, cathode negative ... an induced process as used in electroplating.
It took me years of education to understand this, you are not going to learn it on this forum.

I have nothing to add.

OK, thanks for the info. I'll take a closer look.

[s/v Jedi]

Originally Posted by boatpoker

Do some more research ...
Galvanic corrosion - Anode negative, cathode positive.
Electrolysis - Anode positive, cathode negative ... an induced process as used in electroplating.
It took me years of education to understand this, you are not going to learn it on this forum.

I have nothing to add.

What you say isn’t wrong but that doesn’t mean there can be no electrolysis aboard a boat. It can happen and often even between two neighboring boats like in a marina. I have personally observed it.

Whenever you put an electrical potential on two materials and a current starts flowing between them, you have electrolysis by definition. Galvanic corrosion is without the potential, just submerging two metals is enough.
Also, a metal alloy can experience this (dezincification)

[Fishspearit]

Originally Posted by Fiso

Man, you guys have me baffled in your responses as they make no sense. The Anode (positively charged one) to the Cathode (negatively charged one) flows electrons from the positively ones to the negatively ones. If I charge an ION of a material to the positive charged state, it will flow, and bond, to the one with the positively the charged state. If I bombard and ion of (Name your material here) from the Anode to the Cathode, I deplete one while adding to the other. Name your metal here?

If you do that from a naturally occurring potential difference between the two or an induced potential between the two, what changed physically in that process except what we call it?

This can be a difficult concept to grasp. When thinking about corrosion you need to think in terms of electron flow, not electrical flow like we usually consider for dc current. The electrons actually flow from negative to positive. This is why for galvanic corrosion when you have aluminum (more negative on the galvanic scale) in contact with steel (less negative) then the electrons will flow from the anode (more negative aluminum) to the cathode (less negative steel) while the ions flow through the electrolytic solution exchanging their electrons.

With stray current corrosion or 'electrolytic corrosion' a positive dc power source is applied to an underwater metal. For an example lets use a bronze through hull that inadvertently had a 12 volt wire fall against it. The circuit through the electrolytic solution is completed by the prop and shaft that are connected to DC negative through the engine ground.

Now here's the confusing part. The electrons are flowing FROM the through hull with the positive 12 volt wire on it TO the positive terminal of the battery because the through hull is 'more negative' than the positive terminal and electrons flow from negative to positive. So in this case that through hull with the positive wire touching it becomes the anode, as the electrons are leaving it to flow to the battery, the prop shaft then becomes the cathode, with ions flowing through the water to replace the electrons that are leaving the anode and flowing through the battery.

If you can follow that it explains why with stray current corrosion the anode, or part that loses its metal significantly, is actually the one that has the positive voltage applied and the cathode is the one connected to the battery negative. The positive battery terminal is 'more' positive than the through hull with 12 volts, so the electrons flow towards the battery, making the through hull the anode.

While oversimplified and without an explanation, boatpoker is right that with galvanic corrosion the anode is negative and with stray current corrosion the anode is positive (though less positive than the positive terminal of the battery).

[CharlieJ]

Fishspearit #49 +1
And with stray current corrosion, the placement of the two underwater metals on the Galvanic Series is meaningless.

[boatpoker]

Originally Posted by s/v Jedi

What you say isn’t wrong but that doesn’t mean there can be no electrolysis aboard a boat. It can happen and often even between two neighboring boats like in a marina. I have personally observed it.

Whenever you put an electrical potential on two materials and a current starts flowing between them, you have electrolysis by definition. Galvanic corrosion is without the potential, just submerging two metals is enough.
Also, a metal alloy can experience this (dezincification)

You've witnessed poles of anode and cathode reversing ? Please explain how that happens.

[CharlieJ]

And more basics: In SCC, electrons leave the anode making it positive and travel through the metallic (usually copper wire) through, what can be a tortuous path, back to the B+ of the source. Meanwhile, positive ions (remember, nature distains other than equilibrium) are ejected into the electrolyte and create an ion flow to the cathode which is connected, by another tortuous path to the B- of the source.

Four take aways for understanding SSC:
1. Follow the negatively charged electrons.
2. Unlike charges attract, like charges repel.
3. Electrons flow in metal.
4. Ions flow in electrolyte.

[s/v Jedi]

Originally Posted by boatpoker

You've witnessed poles of anode and cathode reversing ? Please explain how that happens.

I have been trying to tell you all this time but you don’t get it: the poles reverse when you apply an external power source. Like when you charge a battery. You go from a voltaic cell to an electrolytic cell. You convert electricity into chemical energy while charging a battery and this is electrolysis. When you discharge you convert chemical energy into electricity and this is a voltaic cell, or galvanic cell.

So two metals submerged in water create a galvanic cell. This is what you are familiar with. But when you put a DC power supply onto the two metal parts, you get electrolysis. Someone else described it perfectly with a dc positive making contact with a thru hull fitting while the propshaft is connected to dc negative.

But this DC power supply can also be formed between two boats when they are close enough together. The circuit is created via a shorepower connection.

[Fiso]

Originally Posted by Fishspearit

This can be a difficult concept to grasp. When thinking about corrosion you need to think in terms of electron flow, not electrical flow like we usually consider for dc current. The electrons actually flow from negative to positive. This is why for galvanic corrosion when you have aluminum (more negative on the galvanic scale) in contact with steel (less negative) then the electrons will flow from the anode (more negative aluminum) to the cathode (less negative steel) while the ions flow through the electrolytic solution exchanging their electrons.

With stray current corrosion or 'electrolytic corrosion' a positive dc power source is applied to an underwater metal. For an example lets use a bronze through hull that inadvertently had a 12 volt wire fall against it. The circuit through the electrolytic solution is completed by the prop and shaft that are connected to DC negative through the engine ground.

Now here's the confusing part. The electrons are flowing FROM the through hull with the positive 12 volt wire on it TO the positive terminal of the battery because the through hull is 'more negative' than the positive terminal and electrons flow from negative to positive. So in this case that through hull with the positive wire touching it becomes the anode, as the electrons are leaving it to flow to the battery, the prop shaft then becomes the cathode, with ions flowing through the water to replace the electrons that are leaving the anode and flowing through the battery.

If you can follow that it explains why with stray current corrosion the anode, or part that loses its metal significantly, is actually the one that has the positive voltage applied and the cathode is the one connected to the battery negative. The positive battery terminal is 'more' positive than the through hull with 12 volts, so the electrons flow towards the battery, making the through hull the anode.

While oversimplified and without an explanation, boatpoker is right that with galvanic corrosion the anode is negative and with stray current corrosion the anode is positive (though less positive than the positive terminal of the battery).

Excellent description and Thanks to you both. I think the magic words were more and less negative or more and less positive. Any potential difference is, and does, make an anode and cathode. I get it... Thanks again.

[Fiso]

To get back to the OPs problem... We have 9V DC on the ALU cabinet. and 9V DC on the thru hull. AC can be induced. DC is a path. Meter on DC vs AC, right? We have chatted about the Cabinet DC isn't an issue floating, until it is. The 9vdc on the thu-hull is a problem now, er, IMO

I have advocated that there is a source, or a path in some way. MUST BE if true DC, and several of us have advocated that a backwards process of isolation is the key, with suggested t-shooting steps to isolate.

PEDRO: Your turn... How is it going in your testing? You ask for assistance. We are assisting.