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diy solar

Need help please with Victron 500A Smart Shunt readings

Reality check. With 2000W of solar, on a good day, expect about 600Ah of power. So that will only cover half of the 1200Ah battery, the rest will need to come from a generator. Running your A/C for 8 hours will consume 800-900Ah. So you will need the generator daily.

Realistically, you would need 6000W of solar to support a 1200Ah Lithium bank. 4000W to support 1200Ah, and another 2000 to recharge the batteries (over two days, while still supporting your load) after a day of rain. With your current setup you only have 600Ah of power you can use every day, anything more than that will come from the generator.

Just so you understand, with your current parts your goals cannot be met. Of course, you can still make all of your parts work, but expect to run the generator for several hours every evening and every morning as a primary charging source.

Your dilemma seems to surround whether you should go 12p4s, or 4s12p, or something between those. That isn't any easy question, as there are drawbacks to anyway you do it. My biggest issue with 12p is that you have old worn out cells. If one of them fails as a short, there is no way to know. The BMS won't be able to protect from it, and you will have 11 cells directly shorted though the 1 failed cell. That will cause a fire you will be unable to control, and you will loose the boat. 4s12p will protect from that scenario. There are lots of other arguments about keeping the cells balanced, and sharing current equally, keeping all the wires the same length, etc. With 48 old unmatched cells, you are going to have balance issues over time, so that really doesn't matter. You also have some active balancers to take care of those issues.

12p is a lot of cells in parallel. I wouldn't recommend that, even with new cells. But, it will work "ok." That is, It won't work well, but will be ok(ass long as a cell doesn't short). If it were me, I would build 4 packs of 3p4s. You will need 4 BMS's instead of 1, but that is better than needing 12 of them. You will have redundancy if a battery fails and the BMS disconnects it. It is much simpler to build and wire than 12 4s batteries. As for the potential fire issue, the only way to protect from that is 4s12p. But, calb are really well build cells, and shorts are rare. So it is unlikely, but could happen.
I'm only using the AC occasionally anyway. So thats fine. I don't mind using the generator which I've recently replaced every single major component so its now reliable.

I've purchased four Overkill 120A BMS's and have finalized my system as a 3P 4S battery comprised of 12 cells each. This will make 4 batteries for a total of 1,200Ah... (Realistically 1,000Ah with my decreased capacity since the cells are 6 years old and each testing around 85Ah.) You and a few others convinced me that a 12P battery is dangerous. See pic of my latest design.

My question now is:
The previous owner had a QNBBM Lithium Battery Balancer attached to each and every cell in his system. It was 4 cells in series making 12v 100Ah and then 12 batteries in parallel making 1,200Ah. (See pic of balancer)

Should I use these in my 3P 4S battery system? Or is that the job of the Overkill 120A BMS that I purchased?
 

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Its not very clear to me exactly what your objective is.

The BMS in a 4S battery is connected to each cell to monitor each cell voltage and there is the control element, FETs or relay/contactor between the negative of the series connected cells and the negative of the circuit. It monitors current either with an extremal shunt or hall effect sensor, or internal within the package using resistance.

refer to this from resources,

If you only have one 4S BMS it can only monitor 4 cells, it controls the battery made up from those 4 cells in series.
Thus with a single BMS you have no option other to make up each of the 'cells' with 12 of your 100Ah cells in parallel.

The BMS will monitor each parallel set of cells but can only disable the charge and/or discharge paths to the complete battery.

Getting back to your 12P4S concept, electrically there is nothing wrong with this. As I indicated in my last post there is no redundancy so any minor failure or BMS detection of an out of range situation and either the charge or discharge path is turned off.

The original setup was 12 off 4 cell batteries each with an active balancer, QNBBM 4S Lithium Battery Balancer. From my understanding these are very effective at balancing cells connecting in series and will work in conjunction with a BMS.

It may well be the case when the battery pack was installed, using these balancers was the most effective solution at the time., creating a battery pack that that did not have the possibility of a BMS shutdown or malfunction, and having 4 cell batteries with well balanced cells over operational range. The issues you encountered may have been due to poor or inadequate physical interconnections rather than a inherent design failure. Its considered by some sea going users of lithium battery packs that battery shutdown due to BMS action is unsafe.

With suitable charge voltages and monitoring the pack voltage, you could have a system without a BMS, the boat has survived 6 years without such a system. From the cell testing you do not seem to have badly damaged cells and the capacity loss is to be expected after 6 years and perhaps somewhat neglected life.

Mike
I've purchased four Overkill 120A BMS's and have finalized my system as a 3P 4S battery comprised of 12 cells each. This will make 4 batteries for a total of 1,200Ah... (Realistically 1,000Ah with my decreased capacity since the cells are 6 years old and each testing around 85Ah.) You and a few others convinced me that a 12P battery is dangerous. See pic of my latest design.

My question now is:
The previous owner had a QNBBM Lithium Battery Balancer attached to each and every cell in his system. It was 4 cells in series making 12v 100Ah and then 12 batteries in parallel making 1,200Ah. (See pic of balancer)

Should I use these in my 3P 4S battery system? Or is that the job of the Overkill 120A BMS that I purchased?
 

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It would be useful to establish the six year old balancers are working correctly, you have a choice of 12 and only need 4.

The Overkill app displays cell voltages so the actions of the active balancers can easily be seen.

Leaving the balancers on continuously against just using to get an initial balance is something to consider.

Any extra electronic 'stuff' hung on the cells is increasing a possible failure point. Its also possible the active balancer could 'mask' problems developing in the pack.

Mike
 
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Given the age and condition of your cells, yes, use the balancers.
Does it matter if the cells are in 3P 4S? When I took them off the old Setup, they were in 1P 4S. Not sure if the increased amps effects them at all?
 
It would be useful to establish the six year old balancers are working correctly, you have a choice of 12 and only need 4.

The Overkill app displays cell voltages so the actions of the active balancers can easily be seen.

Leaving the balancers on continuously against just using to get an initial balance is something to consider.

Any extra electronic 'stuff' hung on the cells is increasing a possible failure point. Its also possible the active balancer could 'mask' problems developing in the pack.

Mike
I was wondering about that exact thing. How do I test the QNBBM balancers to see if they work properly?

I have 48 of them (still tie wrapped in groups of 4). I’m just worried that they won’t work on a 300Ah battery since the old system was wired 1P 4S 100Ah and my new design is 3P 4S 300Ah.

From what others have said I should leave them on continuously. They probably do a better job at balancing than the BMS. But yeah, it’s another failure point that can hide problems. If the BMS doesn’t do as good of a job as the QNBBM balancers at balancing then I’ll probably use them even though all that extra wiring makes things messy.
 
D

Does it matter if the cells are in 3P 4S? When I took them off the old Setup, they were in 1P 4S. Not sure if the increased amps effects them at all?
No. As far as the balancers can tell, they are still 4s.
I agree with what @mikefitz said. Also, the balancers should not balance all the time, only when the cells are at a high state of charge, 3.4V per cell or more. I am not sure if that is configurable or not. The balancer in the overkill is just very slow/low current. It works fine for smaller batteries, or new batteries in good condition, but may not be able to keep up if you have cells that fall out of balance quickly.

The overkill will give a lot in insight. You could skip the balancers, and then only add them if you see the overkill can't keep up. That would also confirm they work when you need them too.

The lack of a balancer will not damage anything. The battery will just lose capacity as it goes out of balance until you top balance them again.
 
No. As far as the balancers can tell, they are still 4s.
I agree with what @mikefitz said. Also, the balancers should not balance all the time, only when the cells are at a high state of charge, 3.4V per cell or more. I am not sure if that is configurable or not. The balancer in the overkill is just very slow/low current. It works fine for smaller batteries, or new batteries in good condition, but may not be able to keep up if you have cells that fall out of balance quickly.

The overkill will give a lot in insight. You could skip the balancers, and then only add them if you see the overkill can't keep up. That would also confirm they work when you need them too.

The lack of a balancer will not damage anything. The battery will just lose capacity as it goes out of balance until you top balance them again.
Great info.
Ok based on this, I think I’m just going to install the QNBBM Lithium Balancers from Day 1…

As long as it won’t screw up the Overkill BMS then all I have to worry about is the extra wiring and troubleshooting. I think it will give me piece of mind that these extra balancers will help.
 
When you are in the middle of that big blue pond you will need all the system redundancy and reliability that you can get.



Big Blue Pond.......The mighty Pacific Ocean....been there, there are no spare parts out there, or anywhere near close enough to help.
 
Redundancy…
So by that you mean you think I should use the QNBBM Lithium Balancers in addition to the BMS?

Someone brought up the fact that adding 6 year old balancers and extra cables could also be potential trouble for the system and for troubleshooting.
 
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