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The negative cable you point to I believe goes to either the engine battery or a negative bus bar on the other side of the boat...I will confirm exactly where it goes this afternoon.
You cannot do that as the shunt will never see the charging or loads occurring on that wire. That wire needs to be moved to the load side of the shunt. It is now on the battery side....

https://marinehowto.com/installing-a-battery-monitor/
 

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....I did think it odd that they didn't take it off the same battery as the positive, but on a parallel circuit you should be able to connect anywhere on the negative side, unless I am missing something?
It’s my understanding, in order to balance charge and load on all the cells, the pos and neg takeoffs should each be on opposite ends of the parallel bank. The best I can tell, from the limited view, the neg looks in the middle of the bank.
 

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Discussion Starter #23
It’s my understanding, in order to balance charge and load on all the cells, the pos and neg takeoffs should each be on opposite ends of the parallel bank. The best I can tell, from the limited view, the neg looks in the middle of the bank.
Yes that makes sense, however tapping the 4th battery instead of the 5th isn't likely to make much difference. I will improve that when I rewire the batteries, but for now I doubt it is causing a problem.

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.....but for now I doubt it is causing a problem.....
I wouldn't be so sure. The battery that is outside the direct path between the pos and neg takeoffs may have worn prematurely.

I still wonder if the entire charge system is designed for gel profile, which would mean all the batteries were improperly charged.
 

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Discussion Starter #25
So I went down to the boat to take a closer look at the wiring, and compare it to the diagram in the manual. It looks like the boat originally came with 3 house batteries. The 3 on the left are almost as shown on the wiring diagram. The extra negative cable does go to the engine battery, but does not continue on to the negative battery switch as shown in the diagram. Instead there is another negative cable coming off the bottom left battery that I believe goes to the negative switch. (I didn't have time to cut the bundle of cables open to fully verify).

At some point the 2 batteries on the right were added to the system, and that is where the wiring gets even more interesting. It seems that they went to the trouble of adding a long negative cable, the one I added the shunt to, and it goes all the way over to the negative bus bar on the load side of the negative switch.

That explains something that happened a while back: I always turn off the engine battery but leave the house batteries on to power bilge pump etc. Once my wife turned the black negative switch off thinking that was the engine battery. I didn't notice right away, because everything was still working with it off. I thought that was weird at the time...now I know why!

So clearly I need to rewire the batteries, but first I am trying to wrap my head around what they were trying to accomplish by wiring it this way.

I am thinking I just need to rewire as per the diagram with the 5 house batteries instead of 3. I still want the shunt between the last house battery and the engine battery, because I don't want cranking amps being measured on my monitor, just house loads.

Any thoughts?


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.....first I am trying to wrap my head around what they were trying to accomplish by wiring it this way.
You might be giving the PO too much credit and they simply did it incorrectly, especially if they added capacity. Getting 12v to physically work, after connecting all the wires, is not hard. Doing it properly (safely) requires research of non-intuitive factors. This is likely why 12v electrical systems are the number one cause of boat fires. MaineSail provided an excellent link. He's the pro here, not me.

I still want the shunt between the last house battery and the engine battery, because I don't want cranking amps being measured on my monitor, just house loads.
I'm confused by this statement. Do you use the house bank to start the engine or do you have a separate start battery? If you use the house bank, you still want those amps measured through the shunt. If you have a separate start, it should be fully isolated from the house and it's shunt.

The exceptions to isolation may be a cut over switch, where one could change from the start battery to the house, if the start were dead. This should still be done on the load side of the shunt. There can be battery combining charge systems that either switch between the two banks or charges the start off the house too.
 

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The start battery & every DC negative wire on-board the vessel must be on the load side of the shunt.

I don't know how to be any more clear on this.

Your battery monitor errors are due to incorrect shunt wiring. For what it is worth, the US safety standards do not allow a switch in the negative.

Your shunt is no different than the water meter to a house or electric meter or gas meter. If you tap into that piping ahead of the meter you're now stealing power, water or gas from the company providing it. If the shunt cannot see all DC loads (think of it as your electric meter), you're just robbing yourself...

This is what you have done by leaving that large gauge neg wire where it is:

 

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Discussion Starter #28
The start battery & every DC negative wire on-board the vessel must be on the load side of the shunt.

I don't know how to be any more clear on this.

Your battery monitor errors are due to incorrect shunt wiring. For what it is worth, the US safety standards do not allow a switch in the negative.

Your shunt is no different than the water meter to a house or electric meter or gas meter. If you tap into that piping ahead of the meter you're now stealing power, water or gas from the company providing it. If the shunt cannot see all DC loads (think of it as your electric meter), you're just robbing yourself...

This is what you have done by leaving that large gauge neg wire where it is:

The engine battery is separate from the house bank. It shares a negative, but the positive circuit is completely different. The monitor has separate voltage monitoring for the engine battery.

If I installed the shunt after the engine battery then the current flow from starting the engine would register on the battery monitor as a drain on the house bank would it not? Wouldn't that defeat the purpose of the monitor as a tool to measure house bank usage?

I understand that the multiple negative cables coming off the house bank are problematic, and I will correct that, but I don't want the starter amp draw influencing the the house bank monitor when that energy is not coming out of the house bank.

Interestingly, even with the multiple negative connections on the house bank, the amp draw of various loads seem to be measured correctly. It will be interesting to see how much it changes. I suspect the greater impact of the miswiring is on the charging side, and the batteries are not getting fully charged.

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The engine battery is separate from the house bank. It shares a common ground <s>negative</s>, but the positive and negative circuit is completely different.
I think this may be what you are seeing. If so, then it is as it should be. All negatives on a boat should tie to a common ground point, unless they are intentionally isolated systems. Typically, this is the engine block for the house and start batteries, but it could be the start battery negative post. However, this does not mean that the start battery is now in the shunt circuit and monitoring current with the house. The only way it would be wrong is if they are connected together in a circuit and also connected to a different point as a common ground, because that could lead to different ground potentials.

Our start batteries are also electrically connected to the house through a common ground, but our monitor does not see their current.

Mark
 

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Discussion Starter #30
I think this may be what you are seeing. If so, then it is as it should be. All negatives on a boat should tie to a common ground point, unless they are intentionally isolated systems. Typically, this is the engine block for the house and start batteries, but it could be the start battery negative post. However, this does not mean that the start battery is now in the shunt circuit and monitoring current with the house. The only way it would be wrong is if they are connected together in a circuit and also connected to a different point as a common ground, because that could lead to different ground potentials.

Our start batteries are also electrically connected to the house through a common ground, but our monitor does not see their current.

Mark
Yes, ultimately the negatives all end up at a common ground. If you look at the wiring diagram I posted, the negative cable chains from one house battery to the next, and then it goes on to the engine battery, and from there to the negative disconnect switch. After the disconnect switch it gets distributed to various loads, as well as ground.

The point I am trying to make is that if I installed the shunt on the negative cable AFTER the engine battery so that ALL negative connections go through it, then it would be measuring current flow out of the starter battery as well as the house bank. If I put the shunt after the last house battery, and before the engine battery, then I would be measuring only current flow from the house bank, and NOT from the engine battery, which is the goal for a house battery monitor.

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Discussion Starter #31
You might be giving the PO too much credit and they simply did it incorrectly, especially if they added capacity. Getting 12v to physically work, after connecting all the wires, is not hard. Doing it properly (safely) requires research of non-intuitive factors. This is likely why 12v electrical systems are the number one cause of boat fires. MaineSail provided an excellent link. He's the pro here, not me.
That is very possible, but I also think assuming this was a DIY upgrade also gives the PO too much credit. He didn't strike me as a DIY kinda guy, and the additional cable run was done pretty well, and incorporated into the existing wire harness fairly well.

Maine Sail points out that in the US you are not allowed to switch the negative, (although the boat was built in the USA and has both positive and negative disconnect switches. )

Could this extra negative cable run that bypasses the switch be an attempt to make the boat compliant with that regulation? But if that were the case, why wouldn't they simply move the cable from the line side to the load side of the switch, effectively removing it from the circuit?

My instinct is to simply restore the wiring to factory specs as per the wiring diagram. But I don't want to do that until I think it through and make sure there was not a good reason to wire it the way it has been done.

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All negative wires on-board, including the start battery, go on the load side of the shunt. Until you correct this wiring issue the BMV will not work correctly. It should also not be turned off via a negative switch.




If this 5 battery bank is wired in parallel, and the neg wire with green shrink is the neg take-off for the house bank, then the wire marked with the green arrow needs to be moved to the load side of the shunt. You CANNOT jump the shunt and have any chance of Ah counter accuracy..

 

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Discussion Starter #33
All negative wires on-board, including the start battery, go on the load side of the shunt. Until you correct this wiring issue the BMV will not work correctly. It should also not be turned off via a negative switch.




If this 5 battery bank is wired in parallel, and the neg wire with green shrink is the neg take-off for the house bank, then the wire marked with the green arrow needs to be moved to the load side of the shunt. You CANNOT jump the shunt and have any chance of Ah counter accuracy..

Yes, I think we are both saying the same thing in different ways.

When I installed the shunt I connected it using the green heat shrink jumper, to that corner of the bank since that was the main negative connection. What I did not realize was that there is a second negative, coming off the first battery of the bank; the same battery the positive feeder connects to, that ALSO goes to the system negative disconnect. On top of that, the 3rd negative cable that you pointed out, which goes to the engine battery post, but no further. So instead of all of the negative cables forming a single series circuit interconnecting all negative terminals and ultimately leading to the negative disconnect switch, I have a series circuit with a parallel negative connection that forms a second potential current path.

Aside from making the battery monitor data suspect, I think the greater potential problem is that my batteries are not getting charged evenly across the bank.



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If you look at the wiring diagram I posted
Somehow I missed that post. The diagram by MaineSail is how ours are wired, and what I thought yours were, but maybe not in such a direct way. Now I see that you do have a negative on the battery side of the shunt, and that won't work like MS pointed out.

If you move it to the other side of the shunt, the monitor won't see the start battery because start/charge current is not going through the shunt to the house bank anymore.

Mark
 

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Discussion Starter #36
Oops, now I see I also missed your latest post where you described the issue.



Stupid phone - I'm usually on my computer.



Mark
I am just explaining what I have discovered so far, but I still have to cut open the bundles of cable to properly trace everything out and verify.

I appreciate all the feedback from everyone. I didn't expect to have to sort out issues like this on such a new boat, but it is a good way to get to know my systems!

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Now that I have a battery monitor on my boat I am starting to collect information on my battery system. I have only had the monitor for a couple of weeks, and we have yet to spend any time off grid, but already I have noticed some interesting behavior. While the boat is at the dock it is on shore power, and the battery charger is always on. Even with the battery charger on the monitor indicates the batteries are slowly discharging. There are a couple of small parasitic loads on the system, mainly the electronic instrument panel, and the stereo system which is always powered so it maintains clock and radio presets. I would have thought that the battery charger would easily compensate for the small load, but after a week the monitor indicates the SOC is at 97%.

If I cycle the power off and on again on the battery charger it will ramp up it's output to top the batteries up, but eventually the monitor indicates a slow discharge again.

 

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SchockT;2051655936 Even with the battery charger on the monitor indicates the batteries are slowly discharging.[/QUOTE said:
I have been on SP plus solar for 2 weeks so my batteries are completely charged. Currently solar is sleeping and the charger is doing everything and only the freezer/refrig and a fan is running. I looked at my BM and it is reading between +0.012 & -0.05, but mostly is reading 0.00
 

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Now that I have a battery monitor on my boat I am starting to collect information on my battery system. I have only had the monitor for a couple of weeks, and we have yet to spend any time off grid, but already I have noticed some interesting behavior. While the boat is at the dock it is on shore power, and the battery charger is always on. Even with the battery charger on the monitor indicates the batteries are slowly discharging. There are a couple of small parasitic loads on the system, mainly the electronic instrument panel, and the stereo system which is always powered so it maintains clock and radio presets. I would have thought that the battery charger would easily compensate for the small load, but after a week the monitor indicates the SOC is at 97%.

If I cycle the power off and on again on the battery charger it will ramp up it's output to top the batteries up, but eventually the monitor indicates a slow discharge again.

Can't discount that the monitor is not working or set properly, but this may also be a normal function of the charger. Our charger floats for a while, then lets the battery work down some, then brings it up again.

Mark
 

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Discussion Starter #40
Can't discount that the monitor is not working or set properly, but this may also be a normal function of the charger. Our charger floats for a while, then lets the battery work down some, then brings it up again.



Mark
Yes, I think it is a normal function of the charger. Since I turned off boost mode it seems like the batteries are getting a better charge. Having said that, I do still need to rewire the batteries to get rid of the multiple negative connections as I think I am not getting balanced charge across the batteries. I just need to get the materials to make another cable.

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