How to find straycurrents in alternator, solar panels and wind turbine

[Arrandir]

I see now that what I wrote can be interpreted in different ways. It's still 250 mV between chainplate and shroud when I disconnect the negative terminals.
It's 1,5 M ohm between he cables and the windlass.
All readings have been done when it's been dry and with DC. Everything is SS.
I get 40 mV when I have one probe to a shroud and the other in the air. 0 V when the probes touch each other.
I will bring the broken shroud to a rigger within a few days to get a new one and ask for an opinion what they think. Hopefully they can give a better explanation than the last rigger.
For natural causes we have started to discuss other things than what I originally asked about. I found at last an explanation of how to check the alternator. If someone read this with the same question as I had, then you will find the answere in Advanced Marine electrics and electronic troubleshooting. You need a silver silver chloride reference probe.
What about solar panels and windturbine? Is it so rare that there are problems with them so it's not worth checking? As I wrote before, I check for stray currents once in a while so I find the problem before something breaks, but I have only checked the easiest things before.

[CharlieJ]

@Michael Cobb #30
A galvanic isolator is incapable of blocking stray current.

Galvanic isolators block galvanic current and will conduct when the voltage on the safety ground wire > about 2 VDC and will always pass AC to maintain the function of the safety ground wire.

"Stray current corrosion" is a loose term used to describe electrolytic (not "electrolysis!) corrosion and is caused when a DC power source, generally at full battery voltage, is applied to an unbonded underwater metal component which becomes the anode to a cathode that is in contact with the negative of the DC power source.

[s/v Jedi]

Originally Posted by waterman46

I think we interpreted OP Arrandir differently. He wrote:
"8. There is no difference in voltage between chainplates and stays when I disconnect the negative cables."

And BTW, what reading does he get on the meter with the probes held in air near the same location, and with one probe making contact and the other not making contact, and with the two probes connected to each other (meter check).

Ah yes. With the readings he gets between metal and the air while at anchor, it means we really need to get a good multimeter out there.

Arrandir: where are you anchored? In the US?

[flee27]

"Stray current corrosion" is a loose term used to describe electrolytic (not "electrolysis!) corrosion and is caused when a DC power source, generally at full battery voltage, is applied to an unbonded underwater metal component which becomes the anode to a cathode that is in contact with the negative of the DC power source.

So based on this is it correct to say that as long as there is not underwater metals that are unbonded then there is no chance for electrolytic corrosion?

Thanks
Foster

[CharlieJ]

flee27 #34

So based on this is it correct to say that as long as there is not underwater metals that are unbonded then there is no chance for electrolytic corrosion?

Correct. No potential difference; not current flow. Ohm's Law. BTW, eliminating the possibility of stray current corrosion by bonding all of the underwater bits is the primary reason to bond.

[flee27]

Thank you. And to clarify bonding just mean to electrically connect the metals to the DC ground circuit right?

Thanks everyone for the contributions.

Foster

[CharlieJ]

flee #36
Short answer is yes.

To be compliant with ABYC Standards:
1. Bond with AWG 8 tinned conductor (or larger) with green insulation
2. If part of the lightning protection system, use AWG 6 tinned conductor (or larger) with green insulation
3. Each connection to underwater metal component must have resistance < 1 ohm
4. Do not daisy chain connections between components
5. Do not use foil as a "bus"
6. Bus must be drilled and tapped. Cannot use self threading screws
7. For cathodic protection, make connection between hull anode and the bonding system
9. Connect bonding system to B- bus

[Arrandir]

Originally Posted by s/v Jedi

Ah yes. With the readings he gets between metal and the air while at anchor, it means we really need to get a good multimeter out there.

Arrandir: where are you anchored? In the US?

Better multimeter is on the shopping list. I use Uni-T UT210D now. The probes are just a few weeks old. Anything I should look for in a new multimeter except higher accuracy?
I'm in Caribbean, I will sail to Europe soon if I trust the rig enough.

[s/v Jedi]

Originally Posted by Arrandir

Better multimeter is on the shopping list. I use Uni-T UT210D now. The probes are just a few weeks old. Anything I should look for in a new multimeter except higher accuracy?
I'm in Caribbean, I will sail to Europe soon if I trust the rig enough.

Pls be more specific: where are you? I know many people all over the Caribbean and may be able to assist.

[s/v Jedi]

Originally Posted by Arrandir

Better multimeter is on the shopping list. I use Uni-T UT210D now. The probes are just a few weeks old. Anything I should look for in a new multimeter except higher accuracy?
I'm in Caribbean, I will sail to Europe soon if I trust the rig enough.

About the meter: you need one with uA range. My latest is the EEVblog meter which is so much sought after that it’s sold out most of the time. The picture shows the mA and the uA ranges. The Uni-T I linked to earlier has those as well and is cheaper but good enough. For accuracy, compare the number of “digits precision” in the specs.

[Arrandir]

Originally Posted by s/v Jedi

Pls be more specific: where are you? I know many people all over the Caribbean and may be able to assist.

I'm on Martinique.

[s/v Jedi]

Originally Posted by Arrandir

I'm on Martinique.

It’s been many years since we were there, but in the marina in Marin is (used to be) a little electronics repair shop. I forgot the owner’s name but he is the guy to talk to for local knowledge or help... may even have a good multimeter for you.

[bfloyd4445]

Originally Posted by Arrandir

I found some corrosion on the rigging which might be due to straycurrents. I started to look for a source to the problem and I have used Boat owners mechanical and electrical handbook as a guide. I have no silver reference electrode and I don't think I can find it for a while. I don't either have e multimeter with a higher accuracy than 10 mA. I have therefore tested resistance in the electrical system and fixed everything with a resistance of less than 40 k ohm between electrical equipment which should have infinite resistance.
Now it's just alternator, solar panels and wind turbine left. How can I check this? Is it possible without a high accuracy amp meter or silver reference electrode?

Sounds like it may a bonding issue to me. Go over connections and make sure they are all clean and tight. If hooked to shore power the neutral can also be a problem. I have seen situations with open neutral and everything works fine but lots of corrosion because the current was finding alternate paths to ground.

[Steve DAntonio]

Originally Posted by Arrandir

I found some corrosion on the rigging which might be due to straycurrents. I started to look for a source to the problem and I have used Boat owners mechanical and electrical handbook as a guide. I have no silver reference electrode and I don't think I can find it for a while. I don't either have e multimeter with a higher accuracy than 10 mA. I have therefore tested resistance in the electrical system and fixed everything with a resistance of less than 40 k ohm between electrical equipment which should have infinite resistance.
Now it's just alternator, solar panels and wind turbine left. How can I check this? Is it possible without a high accuracy amp meter or silver reference electrode?

While it's possible, rigging corrosion is almost certainly not caused by stray current, either way, while the results of a reference electrode test could be valuable, it will only tell you about corrosion below the waterline, not in the rigging. In order for stray current corrosion to occur, the metal would need to be immersed in an electrolyte,, i.e. water or be very wet continuously. If you are referring to the rigging specifically, the steel wire, that is nearly always the result of crevice corrosion, which is the result of stainless steel living in a wet, oxygen poor environment. It has nothing to do with stray current from a battery, solar panels etc.

Hull anodes and bonding will have no effect what so ever on above the WL corrosion, rigging etc.

Reference electrode testing: https://stevedmarineconsulting.com/w.../10/Anodes.pdf

Stainless steel corrosion: https://stevedmarineconsulting.com/s...miracle-metal/

Corrosion, Stray current and Galavanic: https://stevedmarineconsulting.com/u...osion-mystery/

[bfloyd4445]

Originally Posted by Steve DAntonio

While it's possible, rigging corrosion is almost certainly not caused by stray current, either way, while the results of a reference electrode test could be valuable, it will only tell you about corrosion below the waterline, not in the rigging. In order for stray current corrosion to occur, the metal would need to be immersed in an electrolyte,, i.e. water or be very wet continuously. If you are referring to the rigging specifically, the steel wire, that is nearly always the result of crevice corrosion, which is the result of stainless steel living in a wet, oxygen poor environment. It has nothing to do with stray current from a battery, solar panels etc.

Hull anodes and bonding will have no effect what so ever on above the WL corrosion, rigging etc.

Reference electrode testing: https://stevedmarineconsulting.com/w.../10/Anodes.pdf

Stainless steel corrosion: https://stevedmarineconsulting.com/s...miracle-metal/

Corrosion, Stray current and Galavanic: https://stevedmarineconsulting.com/u...osion-mystery/

Yes stainless steel need to be in contact with oxygen or it will corrode. But you must also keep in mind that a humid marine air can also act as a catalyst for corrosion.