STRAY CURRENT Issues, need help!

[Pedro -Dawn-]

Hey everyone,

Thank you all for your help in advance. I've been scratching my head on this one to exhaustion.

I have a fairly simple electrical system. One bank of 5x 100ah lead acid batteries in parallel + One automotive battery for cranking. Each bank is connected to its own positive bus bar and both to a common negative bus bar. Both positive bus bars combine in a ACR relay.

I have a strip planking wood + fiberglass hull. My batteries are tied to an all wooden box made to fit the batteries. The wooden box is inside an aluminum cabinet. I didn’t even try to connect the whole system and can already measure what i presume to be stray current. I am getting a 9V reading between battery and the aluminum frame for the cabinet. I have 2 bronze through hulls and the one closer to the batteries is getting the same 9V reading. This hole system is made with 3/0 and 4/0 wire to reach the main switch.

Everything is bone dry. I’ve thoroughly cleaned the batteries and box. Upon visual inspection, every cable seems well insulated. I’ve just built this system so cables are all new. I’ve tested continuity, all seems fine. I’ve tested resistance for every cable (0.1 reading), so i assume they are all properly crimped.

Ps1. batteries have been seating around for a year and seldomly being charged. One is newer. Along the week i’ve tested the voltages and they seem to behave well and keep charged.

Ps2. i am not sure how to test sealed stationary lead acid batteries to check if they are doing ok.

Ps3. This system is not yet tied to the engine/shaft/zinc. Everything from the main switch the distribution boxes in the boat is without fuses.

I am at a loss here and any suggestions are welcome.

Thank you.
Pedro

[Wotname]

No answers but I have some questions!

What is the aluminium cabinet connected to i.e. what holds the cabinet in space?

Are you measuring between the Al cabinet and the +ve terminal or the -ve terminal of the battery? If only one, what is the voltage when measuring the other terminal?

What is the ACR relay mounted on?

What happens when you disconnect either or both +ve terminal of the ACR?

[Fiso]

Evening. Good questions from Wotname. Let me take the other side of the thought process for discussions sake.

For me, I am going to assume that your measurement comes from the neg (-VE) terminal of the house batteries. With the negative buses of both banks commonly tied together, then you could be measuring a leakage from the starting bank DC system through just about anything that is also bonded commonly with the cabinet or through hull showing +9Vdc. That could be in any number of ways, (+ or not -) but if all are properly tied to a common low resistance bonding system, then that would be electrically impossible. I would suggest as well that you may have a two-fold problem. Something is providing the +9V somewhere and shows up in the cabinet and through hull and, something is not shunting it properly to the -VE grounding system. Even the offending device itself with a properly grounded connection will drop all the voltage across it and look purely resistive to the source if it is properly grounded.
With the cabinet and one through hull showing +9V and the other zero, then maybe looking for a broken bonding wire might be useful between the three and the Neg bus. Maybe perform a resistance test between each (Batteries disconnected of course)? Any notable resistance between would indicate an open or high resistance connection. The new shiny wiring bits I am sure will be fine, but the old been there for years bits??? Somewhere between them???

I agree with Wotname also that methodical isolation backwards is the process, but instead of just the +VE side, I would also look at the -VE side as well. Somewhere a point of change will occur, and all will make sense then. Good luck sir and let us know how it turns out.

[Pedro -Dawn-]

Originally Posted by Wotname

No answers but I have some questions!

What is the aluminium cabinet connected to i.e. what holds the cabinet in space?

Are you measuring between the Al cabinet and the +ve terminal or the -ve terminal of the battery? If only one, what is the voltage when measuring the other terminal?

What is the ACR relay mounted on?

What happens when you disconnect either or both +ve terminal of the ACR?

Hi Wotname!
The aluminum cabinet is secured with screws to wood blocks epoxied to the hull sides and on top of water tank. It is 40cm above bilge water level.

I got a 9V reading from the +ve terminal of the battery and negative to aluminum.When measuring via -ve terminal, i had a fairly low reading.

The ACR relay, as all other bus bars, etc, are now mounted to 10mm ply inside the cabinet. This was me trying to isolate the components after having problems.

I will also reply to a comment below and provide some additional details!
Cheers

[Pedro -Dawn-]

Originally Posted by Fiso

Evening. Good questions from Wotname. Let me take the other side of the thought process for discussions sake.

For me, I am going to assume that your measurement comes from the neg (-VE) terminal of the house batteries. With the negative buses of both banks commonly tied together, then you could be measuring a leakage from the starting bank DC system through just about anything that is also bonded commonly with the cabinet or through hull showing +9Vdc. That could be in any number of ways, (+ or not -) but if all are properly tied to a common low resistance bonding system, then that would be electrically impossible. I would suggest as well that you may have a two-fold problem. Something is providing the +9V somewhere and shows up in the cabinet and through hull and, something is not shunting it properly to the -VE grounding system. Even the offending device itself with a properly grounded connection will drop all the voltage across it and look purely resistive to the source if it is properly grounded.
With the cabinet and one through hull showing +9V and the other zero, then maybe looking for a broken bonding wire might be useful between the three and the Neg bus. Maybe perform a resistance test between each (Batteries disconnected of course)? Any notable resistance between would indicate an open or high resistance connection. The new shiny wiring bits I am sure will be fine, but the old been there for years bits??? Somewhere between them???

I agree with Wotname also that methodical isolation backwards is the process, but instead of just the +VE side, I would also look at the -VE side as well. Somewhere a point of change will occur, and all will make sense then. Good luck sir and let us know how it turns out.

Fiso, thank you for your reply!!

I have to say at this point there is no bonding system whatsoever installed. I completely redid all wiring on the boat. Everything is brand new. When i started getting problems with only the battery bank sitting in its box, i did not move further.

Also there is no zinc right now as the shaft is disconnected from the engine.

I do have a bonding system tied to common (-), where i will send inverter chassis, mppt chassis, pv panel chassis. I wasn't contemplating bonding the aluminum structure. On a quick note here, i could do so, should i? I read so many things pro and con that this has me confused.

When you say perform a resistance test on the bank, could you please elaborate how would you run this test? With the bank tied together, but disconnected from the rest of the system?

What is weird is that there is so much voltage running in the aluminum that i thought the problem would be more obvious.

Cheers!

[SailingHarmonie]

Remember, voltage is NOT current. You can not diagnose stray current by measuring voltage. You can have voltages present, but NO current flow at all. Tracking down real stray current issues is hard enough without chasing ghosts.

I would strongly suggest you get a copy of Calder's book, Boatowners Mechanical and Electrical Manual he has a very detailed process for determining if you have a problem, how to find it, and how to solve it. It has way more detailed information that we can present here.

Once you understand the correct process you can then ask more directed questions if there are issues you do not understand.

[tanglewood]

It sounds like your AL cabinet is electrically isolated from your ve+ and ve-, correct? You can confirm this by measuring the resistance between the cabinet and ve-, and cabinet and ve+. It should be infinite. Assuming that's the case, then any voltage measurement from the cabinet to either ve+ or ve- is meaningless since the two are electrically floating relative to each other.

[Pedro -Dawn-]

Originally Posted by tanglewood

It sounds like your AL cabinet is electrically isolated from your ve+ and ve-, correct? You can confirm this by measuring the resistance between the cabinet and ve-, and cabinet and ve+. It should be infinite. Assuming that's the case, then any voltage measurement from the cabinet to either ve+ or ve- is meaningless since the two are electrically floating relative to each other.

Hi Tanglewood!! Thank you for the reply.

I just checked both ve+ and - resistance in relation to the cabinet and it is reading infinite (O.L).

My intention was to have this AL cabinet isolated (thus i decided not to include it in the bonding system, of course this can be easily changed).

The weird thing is, once the battery bank is separated and disconnected from the bus bars, i get 0.001V reading from ve- and ve+. Once i tie the bank together this same tests changes to 9V readings.

The same occurs with the thru hull metal. No reading testing each battery separate. The thing is i stopped when i saw a "high" voltage in the thru hull in relation to the system voltage because i was worried about this path corroding my thru hull...

Thanks!!!

[s/v Jedi]

Like tanglewood wrote, your aluminum cabinet is fine, you’re seeing ghost voltages

That said, your plans for a bonding system sound alarming to me! I am not sure where in the world you are, but I recommend you buy a silver chloride reference cell and good multimeter to do the required measurements and find the required amount of zinc anodes.

Also, I recommend to not bond most things (use an isolation transformer for shore power instead) and if bonding anything at all, start with lightning protection by bonding the base of the mast straight down to a lightning rated bonding plate underwater right under where the bonding wire connects to the mast.

Avoid bonding thru-hull fittings. Use plastic (the good ones as discussed often on the forum) or a good quality bronze like Groco. Those will do fine isolated.

For the DC negative connected to the engine and the DC positive to the alternator and starter I recommend a dual pole battery switch to disconnect both, isolating the engine and underwater metals from DC completely. Blue Sea Systems sells such a switch.

[deblen]

Wooden boat-"ghost" voltage-first time I have heard the "ghost" term but is appropriate. Especially with super sensitive digital volt meters.
Try an analogue meter.
or,try pushing one digital meter probe into hull wood and other probe to both bat. terminals & alum. box.
If bats. have been sitting on wood for a year,you probably have some "microamp" leakage due to normal dampness on bat. cases & wood platform/box.
Remove bats. Wash the bat cases & wood box/wood platform with soapy water.Let dry for a couple days & paint inside wood box/wood platform with good gloss oil paint.
Use a sheet of thin plastic on top of wood platform before setting bats. back in wood box.

Cheers/ Len

[Bowdrie]

S/V Jedi is correct.
Bonding thru-hull fittings on a wood hull can be disastrous to the wood surrounding the fitting should any current get into the bonding system.
It leads to hydrolyzation of the wood, destroying the lignin.

[Pedro -Dawn-]

Originally Posted by s/v Jedi

Like tanglewood wrote, your aluminum cabinet is fine, you’re seeing ghost voltages

That said, your plans for a bonding system sound alarming to me! I am not sure where in the world you are, but I recommend you buy a silver chloride reference cell and good multimeter to do the required measurements and find the required amount of zinc anodes.

Also, I recommend to not bond most things (use an isolation transformer for shore power instead) and if bonding anything at all, start with lightning protection by bonding the base of the mast straight down to a lightning rated bonding plate underwater right under where the bonding wire connects to the mast.

Avoid bonding thru-hull fittings. Use plastic (the good ones as discussed often on the forum) or a good quality bronze like Groco. Those will do fine isolated.

For the DC negative connected to the engine and the DC positive to the alternator and starter I recommend a dual pole battery switch to disconnect both, isolating the engine and underwater metals from DC completely. Blue Sea Systems sells such a switch.

Hey Obi Wan, thank you!

I have to say reading about bonding systems makes me more confused than not. I would rather not bond anything. In my case, would you just not bond the electronics carcasses to a bonding system and do without? Even solar panels frame?

In my current case i am not yet connected to the zinc in the prop shaft. I am getting this voltage just from the battery sitting by, connected as a bank, but unconnected to the rest of the system.

I did consider the ghost voltage issue you just mentioned, but when i saw 9V in the thru hull i got anxious. At this point i feel stuck thinking this will dissolve my thru hulls and the boat is going to sink...

Now should i buy the expensive LoZ multimeter? Should i check for current in the thru hull? The system is not yet on.

Sorry for the mess of a response. I am a lawyer, and electricians i hired here in Brazil are using USD20 Aliexpress multimeters, so not confidence inspiring at all..

[s/v Jedi]

Originally Posted by Pedro -Dawn-

Hey Obi Wan, thank you!

I have to say reading about bonding systems makes me more confused than not. I would rather not bond anything. In my case, would you just not bond the electronics carcasses to a bonding system and do without? Even solar panels frame?

In my current case i am not yet connected to the zinc in the prop shaft. I am getting this voltage just from the battery sitting by, connected as a bank, but unconnected to the rest of the system.

I did consider the ghost voltage issue you just mentioned, but when i saw 9V in the thru hull i got anxious. At this point i feel stuck thinking this will dissolve my thru hulls and the boat is going to sink...

Now should i buy the expensive LoZ multimeter? Should i check for current in the thru hull? The system is not yet on.

Sorry for the mess of a response. I am a lawyer, and electricians i hired here in Brazil are using USD20 Aliexpress multimeters, so not confidence inspiring at all..

Okay so you’re in Brazil… I think you can get almost anything there but high taxes and import duty right?

Anyway, some links… here is a reference cell you definitely need: https://boatzincs.com/categories/too...electrode.html

For multimeter, I find the cheapest that is accurate to the mV is this Aneng 8008: https://www.amazon.com/ANENG-AN8008-.../dp/B076GZK62B

For current I’m not so sure, I never used it for that. I like to use an EEVblog meter from Davy Jones which is anupgraded Brymen: https://www.amazon.com/EEVblog-BM235.../dp/B01JZ1ADCO
as you see it’s a different price class but not as much as a Fluke.

Don’t measure voltages like you’re doing now, you need that silver chloride cell reference for that. You hang it overboard and connect it to the multimeter and use just one probe to measure voltages referenced to ground. It comes with a manual explaining it all, incl. How to determine how much zincs you need.

I actually do recommend to ground the solar panel frames and also to use surge suppressors on solar array output, for which you need a ground as well. One ground plate, under the mast like I wrote before.

Do you plan to use shore power? How?

[Fiso]

Hi Pedro,

I have drawn a quick sketch of your circuit as you described. (attached) Does it look accurate?
Your 9Vdc went away when you disconnected and isolated from the bus bars. To me, that says that there must be some obscure relationship (connection) between the thru-hull/cabinet/DC System not able to dissipate to the grounding scheme. Work that backwards by following what is also tied commonly to the busses.

To the Ghost Voltage theory. No takers here on that one. 9Vac can be induced by who knows what gremlins, but 9Vdc has to have path. Just to be sure, you are measuring DCV not ACV? EMF (Electro-motive Force or Voltage) is the force (hence the name Potential) that drives current. Not harming a thing on the cabinet as long as it remains isolated and floating, but the thru-hull, different story… Second is, that given any path ever, the cabinet becomes a current flowing DC connection immediately. Not something, I think I would ignore personally. Sometimes in t-shooting this stuff, that common point could be far removed from the location of measurement.

Me personally, I would start by leaving the GND tied together and remove the House Bank + (pos) terminal to ensure the source is outside those 5 batteries. Voltage present Gnd to cabinet/Thu-hull? (Yes/No)? If Yes, disconnect the Start Batt + (pos) isolating both + (pos) potential DC sources. Now the two banks are completely isolated except for the GND paths. Potential still at cabinet/Thru-hull? (Yes/No) If yes, any AC devices that produce a DC voltage with potential leakage? At some point working backwards, the potential will disappear when something is disconnected and reappear when connected. When you find the source path, then you can start isolating backwards down that path to the offender. When eventually you disconnect the one last offending path, the 9Vdc should disappear and your problem is on that path.

To the bonding system; eeer, whole can of passionate worms on that discussion. Some say yes, some say no. Me personally, I say yes. Keep in mind Bonding and Grounding are technically two different things. Bonding is keeping different metal parts at the same potential so that no current path develops between them. Grounding is providing a path for current flow back to an potential source, ie., the batteries. For me, all should be commonly tied (AC/DC/Bonds). Also, an isolation xfrm isolates you from any external leakage currents by removing any common DC tie to an external source. Only the AC sinewave is mutually inducted into the secondary’s of the xfmr, but no DC path exist. Internal sources though still need grounded/Bonded together, (think Genset / Inverters) so that YOU do not become the path they can flow current through in the event they have a problem.

[s/v Jedi]

Originally Posted by Fiso

Hi Pedro,

I have drawn a quick sketch of your circuit as you described. (attached) Does it look accurate?
Your 9Vdc went away when you disconnected and isolated from the bus bars. To me, that says that there must be some obscure relationship (connection) between the thru-hull/cabinet/DC System not able to dissipate to the grounding scheme. Work that backwards by following what is also tied commonly to the busses.

To the Ghost Voltage theory. No takers here on that one. 9Vac can be induced by who knows what gremlins, but 9Vdc has to have path. Just to be sure, you are measuring DCV not ACV? EMF (Electro-motive Force or Voltage) is the force (hence the name Potential) that drives current. Not harming a thing on the cabinet as long as it remains isolated and floating, but the thru-hull, different story… Second is, that given any path ever, the cabinet becomes a current flowing DC connection immediately. Not something, I think I would ignore personally. Sometimes in t-shooting this stuff, that common point could be far removed from the location of measurement.

Me personally, I would start by leaving the GND tied together and remove the House Bank + (pos) terminal to ensure the source is outside those 5 batteries. Voltage present Gnd to cabinet/Thu-hull? (Yes/No)? If Yes, disconnect the Start Batt + (pos) isolating both + (pos) potential DC sources. Now the two banks are completely isolated except for the GND paths. Potential still at cabinet/Thru-hull? (Yes/No) If yes, any AC devices that produce a DC voltage with potential leakage? At some point working backwards, the potential will disappear when something is disconnected and reappear when connected. When you find the source path, then you can start isolating backwards down that path to the offender. When eventually you disconnect the one last offending path, the 9Vdc should disappear and your problem is on that path.

To the bonding system; eeer, whole can of passionate worms on that discussion. Some say yes, some say no. Me personally, I say yes. Keep in mind Bonding and Grounding are technically two different things. Bonding is keeping different metal parts at the same potential so that no current path develops between them. Grounding is providing a path for current flow back to an potential source, ie., the batteries. For me, all should be commonly tied (AC/DC/Bonds). Also, an isolation xfrm isolates you from any external leakage currents by removing any common DC tie to an external source. Only the AC sinewave is mutually inducted into the secondary’s of the xfmr, but no DC path exist. Internal sources though still need grounded/Bonded together, (think Genset / Inverters) so that YOU do not become the path they can flow current through in the event they have a problem.

Please describe the circuit return path that electrocutes someone with an isolation transformer that didn’t ground their inverter?

Also, it helps to know what your background is, are you an electrical engineer? I am highly surprised that you can draw a diagram of an unknown boat.