Stray Current found - need fix advice

[s/v Jedi]

Originally Posted by Ween

Agreed. If I don't hear a good reason to keep them "bonded" they go away taking the zinc eating with them, as proven by an engineering approach. Thanks for the support.

BTW, my keel coolers didn’t have the zincs and were still fine. You really only need zincs when you have different metals that are connected electrically and both submerged.

[Ween]

Originally Posted by s/v Jedi

BTW, my keel coolers didn’t have the zincs and were still fine. You really only need zincs when you have different metals that are connected electrically and both submerged.

That's the thing. When the units are off (2 years of local sailing and refit didn't need them) then the bonded cooler zincs were protecting the boat and I had to replace them very frequently.

Now when the coolers are active their zincs last forever as opposed to the shaft and prop zincs that erode away.

After I follow your lead, all that pain goes away as the tiny cooler zincs aren't protecting the whole boat. yay

[s/v Jedi]

Originally Posted by Ween

That's the thing. When the units are off (2 years of local sailing and refit didn't need them) then the bonded cooler zincs were protecting the boat and I had to replace them very frequently.

Now when the coolers are active their zincs last forever as opposed to the shaft and prop zincs that erode away.

After I follow your lead, all that pain goes away as the tiny cooler zincs aren't protecting the whole boat. yay

Exactly. My whole boat, I only have a zinc on the back of my Maxiprop and one single on the prop shaft.

[Fishspearit]

Originally Posted by Ween

Agreed. If I don't hear a good reason to keep them "bonded" they go away taking the zinc eating with them, as proven by an engineering approach. Thanks for the support.

There are several reasons we bond, not just to prevent the risk of AC electrical shock if an ungrounded AC conductor shorts against the DC negative system as Jedi alluded to. The other reason is in the event of a real stray current situation, which I don't think you have, on a bonded system you would most likely trip the circuit breaker powering the ungrounded DC conductor that is causing the stray current(which is why ABYC recommends minimum of 8awg bonding wires, so they can carry this fault current until the breaker trips). On an unbonded system like Jedi advocates for there will not be a continuous path for current through the circuit breaker but there will be a path through the water for the ions that cause the corrosion damage. (unless you have also completely isolated your engine shaft and every other under water metal from the DC negative system as well).

Originally Posted by Ween

Started with hull reference potential -939mV so all good for my glass hull....... Both on -955mV so 16mV potential gain - well above the 10mV cutoff per boatzincs guide.

This is why I question that you have a stray current problem. With the compressors running you are more negative. That means your boat is MORE protected. Stray current usually shows up on the reference probe as moving significantly towards being more positive, and not just 15 mV but in the hundreds of mV or even Volts.

I would be curious to know what the reference potential of just the keel cooler is sitting at. Connect to the bonding wire you removed for the cooler and check that with compressors off and with the compressors on. Copper-Nickel should have a voltage of -.21 to -.28, so with the minimum of zincs it needs to be -.48 or more negative to be properly protected. This will also tell you which zincs you would expect to be consumed faster, shaft or cooler.

There are many things that affect anode consumption such as salinity, current flow, how often the boat is used, etc.

[s/v Jedi]

Originally Posted by Fishspearit

There are several reasons we bond, not just to prevent the risk of AC electrical shock if an ungrounded AC conductor shorts against the DC negative system as Jedi alluded to. The other reason is in the event of a real stray current situation, which I don't think you have, on a bonded system you would most likely trip the circuit breaker powering the ungrounded DC conductor that is causing the stray current(which is why ABYC recommends minimum of 8awg bonding wires, so they can carry this fault current until the breaker trips). On an unbonded system like Jedi advocates for there will not be a continuous path for current through the circuit breaker but there will be a path through the water for the ions that cause the corrosion damage. (unless you have also completely isolated your engine shaft and every other under water metal from the DC negative system as well).

This is why I question that you have a stray current problem. With the compressors running you are more negative. That means your boat is MORE protected. Stray current usually shows up on the reference probe as moving significantly towards being more positive, and not just 15 mV but in the hundreds of mV or even Volts.

I would be curious to know what the reference potential of just the keel cooler is sitting at. Connect to the bonding wire you removed for the cooler and check that with compressors off and with the compressors on. Copper-Nickel should have a voltage of -.21 to -.28, so with the minimum of zincs it needs to be -.48 or more negative to be properly protected. This will also tell you which zincs you would expect to be consumed faster, shaft or cooler.

There are many things that affect anode consumption such as salinity, current flow, how often the boat is used, etc.

You seem to have missed that the OP has a silver chloride reference cell. This means that there is no room left for speculations as factual measurements are clear.

[Fishspearit]

Originally Posted by s/v Jedi

You seem to have missed that the OP has a silver chloride reference cell. This means that there is no room left for speculations as factual measurements are clear.

You seem to have missed that I literally quoted the OP's reference cell measurements in my comment.

Perhaps an Electrical Engineer can explain how a stray current problem will cause the reference cell to read MORE Negative. I would look forward to reading that and improving my knowledge base.

I think the OP missed the part in his Boatzincs manual, on page 8, where it specifically mentions the 10mV shift. "After plugging in the AC power cable, a lower reading (more positive) of:
*Over 10mV indicates the vessel's sacrificial anodes are interacting.......
*Over 100mV indicates electrolytic corrosion of the anodes......

[s/v Jedi]

Originally Posted by Fishspearit

You seem to have missed that I literally quoted the OP's reference cell measurements in my comment.

Perhaps an Electrical Engineer can explain how a stray current problem will cause the reference cell to read MORE Negative. I would look forward to reading that and improving my knowledge base.

I think the OP missed the part in his Boatzincs manual, on page 8, where it specifically mentions the 10mV shift. "After plugging in the AC power cable, a lower reading (more positive) of:
*Over 10mV indicates the vessel's sacrificial anodes are interacting.......
*Over 100mV indicates electrolytic corrosion of the anodes......

I’m not sure on your intentions here. Are you here for arguing or are you suggesting that OP has a hidden problem or are you suggesting that he is doing the measurements wrong?

I’ve given up on arguing and I think the OP is fine as I trust he followed instructions from the manual. There are many details like hull materials, type of engine etc. that only he knows for sure.

[Ween]

Originally Posted by Fishspearit

I think the OP missed the part in his Boatzincs manual, on page 8, where it specifically mentions the 10mV shift. "After plugging in the AC power cable, a lower reading (more positive) of:
*Over 10mV indicates the vessel's sacrificial anodes are interacting.......
*Over 100mV indicates electrolytic corrosion of the anodes......

No. On the next page test 4 the same manual states:

"systematically turn off and on each DC circuit break and and its attached equipment...look for a shift in hull potential over 10mV...rapid shift indicates electrical leakage...from either the equipment or its DC power wiring"

this says nothing about + or - direction of shift - just 10mV shift.

This is the source of my concern and still waiting for Frigoboat to explain my -160 mV and 0.4 A readings between the -/com probe on negative bus and + probe on coolers

Again, thanks everyone for your guidance.

[Fishspearit]

I'm absolutely not here to argue. OP asked for a reason to keep it bonded, I explained the reasons we bond. I also think the diagnosis is wrong, I don't think a more negative shift is a sign of stray current, I think it would be a more positive shift that would indicate stray current. A more negative reading means that your underwater metals are MORE protected, not less. So the manual didn't repeat itself about the direction on the next page, ok. I spent quite a while studying electron flow, ion flow, cathodes & anodes, etc. in order to do very well on my ABYC Corrosion certification exam. I use my reference cell on as many boats as I can. I know there's always someone out there who knows more than me, but I don't think your readings are indicative of a stray current problem. That's my opinion, I don't mind at all if you ignore it. By all means remove your bonding wire, it's unlikely to do much damage in the long run, but I also don't think it's going to help anything. The more negative shift means your zincs will be consumed slower when the compressors are running than without them.
But maybe I'm wrong. If I am I truly do want someone to explain why I'm wrong so I don't make this mistake again.

[Ween]

I just want to know why my fridge has DC current to/through the coolers.

I did all the tests right. I only have a shift at the reference electrode when I turn on a device I have clearly shown has in-water voltage.

Whether this is the cause of my zinc erosion we can find out later once the above is resolved.

[Fishspearit]

Ok, I called an expert, Bob at Boatzincs their corrosion engineer. He confirmed what I thought, the negative shift is not stray current and is actually a favorable condition. He said the reasons for the shift are likely due to a voltage drop in the wiring when the compressors are on. He said it's not that unusual and does not believe that you have a problem.

Of course I only know what you've posted. You might want to call him yourself and discuss it first hand, he was very friendly and helpful.

[s/v Jedi]

I think the Frigoboat installer made some errors with the wiring. With the DC negative connected to the bonding system, all sorts of trouble appear that may not be obvious.

For example, in this case the installation may have high resistance in the DC negative of the power feed and this may result in part of the DC current to return via the bonding system instead of the DC negative wire.

My position is based on the impression I have on the position the OP finds himself in, as well as on the measurements and my direct experience with these keel coolers.

When the OP had given me the impression that he is a perfectionist and wants every aspect of his electrical installation optimal, then I would suggest to start with accurately measuring DC current through both DC positive and DC negative conductors. This would have shown a difference if my suspicions are correct.

But the OP is fine; the readings with the reference cell show that he is adequately protected against galvanic corrosion (-900-something mV) and that he can make sure by future testing. Also, these keel coolers are fine without bonding as experience has shown.

So this means the OP is fine with just leaving the bonding system disconnected from the keel coolers. It also proves that there is actual DC negative wiring in place or the fridges wouldn’t work (I have seen installations using the bonding wire as DC return).

The number one thing the OP can do to make his boat’s installation better is to replace the galvanic isolator with an isolation transformer and that’s only needed when he actually uses shore power.

I agree that a more negative reading indicates a more protected balance and that he is well within his zinc’s protective umbrella, but it’s still better with these bonding wires disconnected.

Never accept bonding wires to be part of DC circuits.

[Fishspearit]

Originally Posted by s/v Jedi

I think the Frigoboat installer made some errors with the wiring. With the DC negative connected to the bonding system, all sorts of trouble appear that may not be obvious.

For example, in this case the installation may have high resistance in the DC negative of the power feed and this may result in part of the DC current to return via the bonding system instead of the DC negative wire.

Now we're on the same page Jedi. I hadn't caught how the bonding connection was made, but reading back through the thread I caught it this time.

"The installer wired the cooler bonding plates to the negative bus they installed next to the fridge power panel and controls on the port side of the boat."

This makes perfect sense now. The cooler bonding wire should have been run to the single bonding point on the vessel, wherever that is. You can't just bond to any DC negative point without creating loops. I now suspect that's what's causing the problem. I bet if the cooler bonding wire were run to the correct place then the reference cell would remain steady when cycling the units on and off.

[s/v Jedi]

Originally Posted by Fishspearit

Now we're on the same page Jedi. I hadn't caught how the bonding connection was made, but reading back through the thread I caught it this time.

"The installer wired the cooler bonding plates to the negative bus they installed next to the fridge power panel and controls on the port side of the boat."

This makes perfect sense now. The cooler bonding wire should have been run to the single bonding point on the vessel, wherever that is. You can't just bond to any DC negative point without creating loops. I now suspect that's what's causing the problem. I bet if the cooler bonding wire were run to the correct place then the reference cell would remain steady when cycling the units on and off.

Exactly, plus there is difficult or no access at all to at least parts of this wiring incl. the keel coolers themselves. So I just came up with a solution that is safe for boat and crew instead of a very difficult path to where the installation may be better but the end result is just the same

[Ween]

wow, great dialog and advice.

Yes I imagine the cooler bonding wires, instead of being routed (easy job taken) to the same DC negative bus used for the fridge installation, should be lengthened and bonded to the bonding system junction way back in the boat where the DC neg from battery and all bonding lines meet otherwise.

Maybe someday I'll do this and test again.

But for now I'll feel good that "more negative" hull potential is not a problem.

Can't wait to hear from Frigoboat as to why there is a current on the cooler and thus why they are adamant that the cooler be routed to DC negative even if the coolers are zinc'd.