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

[CharlieJ]

Row Bear
No electrolyte in your scenario. No electrolyte, no ion flow. No ion flow, no stray current (aka, electrolytic) corrosion.

[Arrandir]

One more thing I found during the last riginspection was dots like on the picture on the mast. There where a few when I bought the boat, I did not think so much about it, the mast is probably from mid 80th. This time I thought that maybe there are more, but I'm not sure. Could that have something to do with the problems with the shrouds?
I have a multimeter, but the accuracy is just 10 mA, which is not enough for some tests. I did the voltage test, I had not heard about it before, have only measured resistance. I decided to test this even if it seems like if I don't have problem with stray current.
I disconnected two shrouds. It measured 250 mV. I removed all cables to plus terminals, stoped windturbine, disconnected solar panel and put two towels and a thick blanket over it. I washed the batteries to make sure no dirt let electricity through. No alternator on and no shore power. I still get the same reading. I thought it was something wrong with the multimeter. Almost 0 volt when the probes are disconnected. I get other readings in other places, always about the same reading between the same points.
What could be the reason for this? Where is the voltage coming from?

[a64pilot]

Originally Posted by Row Bear

Could there be a faulty electrical connection to equipment mounted on the mast such as mast head light, steaming light etc. Resulting in a stray current?

I would eliminate the possibility of someone in the past using the mast as a ground path. It’s pretty common in automobile wiring to use the chassis itself as a ground, saves on wiring.

[s/v Jedi]

You really need that better meter before you can start to make sense of readings. It is very unlikely to measure the same 250mV between all kind of different metal parts.

Are you at a dock or at anchor?
Do you have a shore power cord installed, even with the breakers off?
Do you have a galvanic isolator?
Do you have a bonding plate (Dynaplate)?
Do you have bonding wires anywhere?
Is the prop shaft isolated (infinite resistance) from the engine block?
Is the engine block connected to battery negative?
What happens with the 250 mV when you disconnect both battery negative and positive cables?

[donradcliffe]

Do you have a masthead VHF antenna with the antenna ground (sheath on the coax) making electrical contact with the mast?

[Arrandir]

I really appreciate your help. Thanks!

Originally Posted by s/v Jedi

You really need that better meter before you can start to make sense of readings. It is very unlikely to measure the same 250mV between all kind of different metal parts.

Are you at a dock or at anchor?
Do you have a shore power cord installed, even with the breakers off?
Do you have a galvanic isolator?
Do you have a bonding plate (Dynaplate)?
Do you have bonding wires anywhere?
Is the prop shaft isolated (infinite resistance) from the engine block?
Is the engine block connected to battery negative?
What happens with the 250 mV when you disconnect both battery negative and positive cables?

The multimeter is accurate for voltage, 0,1 mV. The problem is the accuracy for current.

1. I'm at anchor.
2. I very rarely connect to shorepower or visit marinas.
3. No galvanic isolator.
4. I have a grounding plate, but only for the wind turbine. It corroded and I need to take it off and clean it on the next haul out. While I wait for that I have a wire connected to the wind turbine's grounding cable.
5. No bonding wires.
6. It's almost infinite resistance between engine block and propshaft.
7. Engine block is connected to battery negative.
8. There is no difference in voltage between chainplates and stays when I disconnect the negative cables. ]

[s/v Jedi]

Originally Posted by Arrandir

I really appreciate your help. Thanks!

The multimeter is accurate for voltage, 0,1 mV. The problem is the accuracy for current.

1. I'm at anchor.
2. I very rarely connect to shorepower or visit marinas.
3. No galvanic isolator.
4. I have a grounding plate, but only for the wind turbine. It corroded and I need to take it off and clean it on the next haul out. While I wait for that I have a wire connected to the wind turbine's grounding cable.
5. No bonding wires.
6. It's almost infinite resistance between engine block and propshaft.
7. Engine block is connected to battery negative.
8. There is no difference in voltage between chainplates and stays when I disconnect the negative cables. ]

This tells us a lot. Next tests:

1. Keep batteries connected but remove grounding cable from wind generator. Do the voltages measured between chainplates and stays go away?

2. What is the resistance between battery negative and different metal parts like chain plates etc.

3. Do you have an electric windlass? If so, what is the resistance between the metal housing and negative cable terminal? You can see how the positive cable terminals are insulated on the windlass motor... is the negative the same? If not, remove negative cable from windlass and try voltage measurements on rigging again.

Note: when you are at anchor and have a chain rode from all the way up to a windlass, this is a grounding point. It also has a different potential than a grounding plate, i.e. a current can flow through the chain via battery negative to the ground plate. A good windlass has an insulated negative terminal. If not, negative needs to be disconnected when not using it.

[donradcliffe]

Did you change the masthead VHF antenna when you re-rigged? If so, disconnect the antenna at the back of the radio and remeasure your voltages.

[s/v Jedi]

Originally Posted by donradcliffe

Did you change the masthead VHF antenna when you re-rigged? If so, disconnect the antenna at the back of the radio and remeasure your voltages.

We’re close and covering all directions

[Arrandir]

No change in voltage when I disconnect antenna and grounding to windturbine.
It's 4 M ohm between chainplate and stay. It's around that high resistance between negative terminal and different parts of the rig too.
The rigger said it was probably the windlass, his experience is that it's the most common reason to stray currents. The windlass itself don't have any plus or minus cable. It's a solenoid under a bed where the cables are connected. The cables which continue to the windlass shift between being negative and positive depending on if the anchor should come up or down. I have had some problems with the solenoid and there have not been any electricity there during any test.
The resistance between windlass case and both cables are around 400 k ohm.

[s/v Jedi]

Originally Posted by Arrandir

No change in voltage when I disconnect antenna and grounding to windturbine.
It's 4 M ohm between chainplate and stay. It's around that high resistance between negative terminal and different parts of the rig too.
The rigger said it was probably the windlass, his experience is that it's the most common reason to stray currents. The windlass itself don't have any plus or minus cable. It's a solenoid under a bed where the cables are connected. The cables which continue to the windlass shift between being negative and positive depending on if the anchor should come up or down. I have had some problems with the solenoid and there have not been any electricity there during any test.
The resistance between windlass case and both cables are around 400 k ohm.

Inspect the motor of the windlass, where the cables attach. Both should be insulated from the metal mousing. Post a picture if you’re not sure.

You can remove both cables from the windlass motor and then measure resistance between the metal housing and each of the terminals.

We need to positively identify where the leak is.

[waterman46]

Originally Posted by s/v Jedi

Inspect the motor of the windlass, where the cables attach. Both should be insulated from the metal mousing. Post a picture if you’re not sure.

You can remove both cables from the windlass motor and then measure resistance between the metal housing and each of the terminals.

We need to positively identify where the leak is.

From any of the evidence, do any of you think the OP has shown that he actually has a leakage current problem?


OP originally got into this investigation because a rigger claimed the corrosion in his lower shroud was caused by stray current. To me it looks like he already eliminated such possibility, though he still needs to put a microammeter between the shroud and the chainplate. Will be waiting for that result.

He measured 250mV between shroud (from turnbuckle I suppose) and the chainplate. But 4Mohm between chainplate and boat grounds. I assume the chainplate, shroud and turnbuckles are all SS so is any galvanic voltage possible? Could the material of the meter's probes cause a galvanic response? Anyway when he measures, is everything dry? Sure the meter was on DC volts not AC?

Still looks like bad SS in the shrouds, with corrosion caused in the usual way.

[s/v Jedi]

Originally Posted by waterman46

From any of the evidence, do any of you think the OP has shown that he actually has a leakage current problem?


OP originally got into this investigation because a rigger claimed the corrosion in his lower shroud was caused by stray current. To me it looks like he already eliminated such possibility, though he still needs to put a microammeter between the shroud and the chainplate. Will be waiting for that result.

He measured 250mV between shroud (from turnbuckle I suppose) and the chainplate. But 4Mohm between chainplate and boat grounds. I assume the chainplate, shroud and turnbuckles are all SS so is any galvanic voltage possible? Could the material of the meter's probes cause a galvanic response? Anyway when he measures, is everything dry? Sure the meter was on DC volts not AC?

Still looks like bad SS in the shrouds, with corrosion caused in the usual way.

Well yes, the 250mV goes away when the battery negative cable is disconnected from the batteries. Somehow there is a connection.

[waterman46]

Originally Posted by s/v Jedi

Well yes, the 250mV goes away when the battery negative cable is disconnected from the batteries. Somehow there is a connection.

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."

I interpret "no difference" meaning he gets the same 250mV measurement both with and without the "negative cables" whatever those cables are. He did not say the voltage dropped to zero.

Perhaps Arrandir can clear up this confusion. Did he get 250mV with AND without those other grounds connected?


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).

[Michael Cobbe]

To stop stray currnet corrosin our boat was ffitted with a galvanic isolator on the 12 volt and 240 volt earth wires.