Batteries shutting down long before capacity is consumed

[Grand Adventure]

I am absolutely stumped by what’s going on, and need some help. Please understand that I only have enough knowledge to be dangerous, so please keep any replies basic so that I can fully understand.

By way of background, my RV’s system consists of a Victron MultiPlus-II 2x 120V 12/3000, a Victron SmartSolar MPPT VE.Can 150/100, a Victron BMV-712 Smart Shunt & Battery Monitor, 1200 W of solar, and 500 Ah of LiFePO4 battery capacity in a bank of five 100 Ah Battle Born batteries. At one time, the battery bank had six of those Battle Born batteries, but earlier this summer I started having issues similar to what I’m about to describe below, and I thought that I found one battery with a questionable BMS, and removed it from the system. At the same time, I cleaned up my battery bank to tie each battery separately and directly to 600A bus bars, with the cables all as short as possible (24”) and of equal length. I’ve since been on hookups most or all of the time, so I haven’t until now really had the chance to see what difference removing that battery made, until now.

We arrived at this dry campsite on Sunday afternoon. I was awakened by a low voltage alarm from the MultiPlus-II at 4am Monday morning, just before the batteries shut off, too, due to low voltage. Going into the VRM to try to see what happened, SOC showed 62% at the time of shutdown (of course, the shunt calculates SOC based on amp-hours consumed), yet voltage had dropped to ~ 10V.

I chalked it up to forgetting to switch the absorption refrigerator from AC mode to propane. At this time of year I’m barely peaking over 500W of solar from my 1200W system, so on Monday night I topped off with the generator, barely reaching absorption before having to the generator off when generator hours ended at 8 pm. I awoke yesterday morning to 67% SOC and ~ 12.8V (of course, under load), so I assumed all was good.

Last night, I again topped off with the generator, barely reaching absorption by the end of generator hours at 8pm.

I awoke this morning at 7:45 a.m. at 66% and ~12.8V (again, under load). I brewed some coffee and started working. Once the coffee maker finished the battery monitor showed 12.60V and 66% SOC. What I need for work creates an AC load on the MultiPlus-II of just over 200W. It seemed to be a similar situation as the day before, so I thought little of it. The rising sun wasn’t yet high enough to produce enough power to exceed consumption, so I was still slowly discharging. Just now at almost 9am, I was startled when the low voltage alarm went off and the MultiPlus-II shut down due to the low voltage. I checked the VRM and the batteries showed 62% SOC and 10.2V when the low voltage alarm went off.

So, it’s always happening at around 62% SOC as calculated by the shunt, which is after I’ve consumed only ~190 Ah of a 500 Ah battery bank. At around 65% SOC the voltage plunges from around 12.55V (again, under load) to barely over 10 V.

Help!!

 

[Mattb4]

Looks like your SOC reading is inaccurate:

 

[OgreMustCrush]

If you are actually reaching absorption, it sounds like you have a lot less actual capacity than your shunt is programmed for, perhaps some batteries have failed and their BMS isn't actually allowing charge/discharge? Or maybe they are horrifically out of balance and not actually getting fully charged, just a runner cell hits OVP and BMS turns off because of it. How are you monitoring that you reached absorption, just checking that the voltage is above 14V or so, or is the shunt actually getting to that voltage and seeing the charge current fall below the tail current setting so it resets the SoC to 100%. I'm assuming you are using reasonable settings on the shunt for LiFePO4 batteries.

 

[SouthernSolar]

Did you change the capacity of your battery bank in the shunt after removing the bad battery ?

 

[Grand Adventure]

Looks like your SOC reading is inaccurate:

View attachment 342760

SOC was reset within the battery monitor upon achieving full charge with the generator. Realize that those voltage readings are under load, whereas as I understand it, that chart denotes SOC at rest.

 

[Grand Adventure]

Did you change the capacity of your battery bank in the shunt after removing the bad battery ?

Yes, reset for 500 Ah.

 

[Grand Adventure]

If you are actually reaching absorption, it sounds like you have a lot less actual capacity than your shunt is programmed for, perhaps some batteries have failed and their BMS isn't actually allowing charge/discharge? Or maybe they are horrifically out of balance and not actually getting fully charged, just a runner cell hits OVP and BMS turns off because of it. How are you monitoring that you reached absorption, just checking that the voltage is above 14V or so, or is the shunt actually getting to that voltage and seeing the charge current fall below the tail current setting so it resets the SoC to 100%. I'm assuming you are using reasonable settings on the shunt for LiFePO4 batteries.

I'm seeing the MultiPlus-II switch to absorption mode, and watching the charging current drop as a result. That's what I'm using to verify that I've reached absorption. And yes, the shunt (and solar charger and inverter/charger) are all configured with Battle Born's recommended settings.

 

[Mattb4]

SOC was reset within the battery monitor upon achieving full charge with the generator. Realize that those voltage readings are under load, whereas as I understand it, that chart denotes SOC at rest.

While true that under load voltages slump but your SOC is reading much higher than the capacity you actually have. One way to quickly check is to remove load and wait for a minute of two and read battery voltage. Compare it to chart. If SOC from chart is much lower than your equipment reports that your readings are wrong.

 

[Suijkerbuijk]

You can have bms soc drift .
That means that the battery bms do not show the correct % vs soc .
The Victron shunt is correct and the battery is 10volt.
Means its 2.5 cell volts.

So you have to do bms reset.
On my battery i do it like this .
Full charge the battery with no load on it .
After that i use overkill solar app that my battery works with.
I adjust the balance charge on or of and save the file.
On that moment the bms reset with the new save file.
After that i set the balance charge in de app back to charge and save again.
This is a risk to do so .

So wait if somebody have a other option

Than again so what that bms is not correct .
The bms safety systeem do work even if the soc % is wrong .
So use the shunt information for the real amp and volt .

 

[Grand Adventure]

While true that under load voltages slump but your SOC is reading much higher than the capacity you actually have. One way to quickly check is to remove load and wait for a minute of two and read battery voltage. Compare it to chart. If SOC from chart is much lower than your equipment reports that your readings are wrong.

Thanks. I'll do that later today once I no longer need power for work, and will report back.

 

[Grand Adventure]

You can have bms soc drift .
That means that the battery bms do not show the correct % vs soc .
The Victron shunt is correct and the battery is 10volt.
Means its 2.5 cell volts.

So you have to do bms reset.
On my battery i do it like this .
Full charge the battery with no load on it .
After that i use overkill solar app that my battery works with.
I adjust the balance charge on or of and save the file.
On that moment the bms reset with the new save file.
After that i set the balance charge in de app back to charge and save again.
This is a risk to do so .

So wait if somebody have a other option

Than again so what that bms is not correct .
The bms safety systeem do work even if the soc % is wrong .
So use the shunt information for the real amp and volt .

You'll have to forgive me, but I'm really not fully understanding what you're suggesting here.

 

[Suijkerbuijk]

You'll have to forgive me, but I'm really not fully understanding what you're suggesting here.

Q&A: SOC Drift in Off-Grid ESS—Causes and Fast Fixes

Frustrated by inaccurate battery readings? Fix SOC drift in your off-grid ESS with our expert guide on causes, fast fixes, and proper SOC calibration.

www.anernstore.com

More brain food

 

[Grand Adventure]

Q&A: SOC Drift in Off-Grid ESS—Causes and Fast Fixes

Frustrated by inaccurate battery readings? Fix SOC drift in your off-grid ESS with our expert guide on causes, fast fixes, and proper SOC calibration.

www.anernstore.com

More brain food

Thank you.

 

[Mattb4]

SOC or state of charge is a percentage number. It is not a capacity number. A 5ah battery can have the same SOC as a 100ah battery but obviously much less capacity at 100%SOC. Just like a fully charged 5ah cell at 3.40v is the same voltage for a fully charged 100ah cell at 3.40v

BTW, it is entirely possible your capacity for your batteries are less than their rated amount. Batteries can wear out, fail or not be properly charged. If so the SOC indication of a shunt will be off because it has a wrong total expected capacity to work from.

 

[Grand Adventure]

SOC or state of charge is a percentage number. It is not a capacity number. A 5ah battery can have the same SOC as a 100ah battery but obviously much less capacity at 100%SOC. Just like a fully charged 5ah cell at 3.40v is the same voltage for a fully charged 100ah cell at 3.40v

BTW, it is entirely possible your capacity for your batteries are less than their rated amount. Batteries can wear out, fail or not be properly charged. If so the SOC indication of a shunt will be off because it has a wrong total expected capacity to work from.

Understood. The batteries in this bank are all approximately 4 years old, so I shouldn't expect them to be off by that much?

 

[Suijkerbuijk]

Understood. The batteries in this bank are all approximately 4 years old, so I shouldn't expect them to be off by that much?

No
THis type of battery the chemical inside are good for 20 years .
Most battery can run without problems for 10 years my own battery are from 2021 .
And running 24/7
My place is a boat .
So for my self i use solar , wall power by a battery charger and the engine to charge the systeem back up.
So in the winter type its run full on chargers .lol.

 

[marionw]

You need to get the batteries fully charged. Monitor/check individual cell voltages if possible and check/verify that the BMS has started to balance the cells. Try to get cells to at least 3.45 volts. If you have an excessive cell voltage differential and one or more "runner" cells are charging to the Cell Over Voltage Protection set point then the BMS will shut down further charging and as a result the BMS reported SOC will be inaccurate and the battery capacity will be reduced.

Once you get the batteries full charged then you also need to reset the shunt so it now has the correct SOC reference.

 

[time2roll]

What is shutting down (battery or inverter) and what is the error message?
What is the charging voltage? Is current flowing into the battery smoothly during charge right up to 14.2+ volts? This is to verify no battery shut down when charging.
Probably best to separate and test the five batteries individually.

 

[Grand Adventure]

You need to get the batteries fully charged. Monitor/check individual cell voltages if possible and check/verify that the BMS has started to balance the cells. Try to get cells to at least 3.45 volts. If you have an excessive cell voltage differential and one or more "runner" cells are charging to the Cell Over Voltage Protection set point then the BMS will shut down further charging and as a result the BMS reported SOC will be inaccurate and the battery capacity will be reduced.

Once you get the batteries full charged then you also need to reset the shunt so it now has the correct SOC reference.

As far as I know, without Bluetooth capability in these batteries I don't have a way to check individual cell voltages, although someone may feel free to correct me. And yes, I reset the battery monitor/shunt to 100% after fully charging on Monday.

 

[wpns]

Sounds like only a couple of your batteries are properly functional, I’d get a clamp-on DC ammeter and ensure all the batteries are charging and discharging around the same rate.

And then, because running 5 in parallel is going to be a nightmare, take them out one at a time, fully charge them till balancing is complete (oops, hard to do without comms, maybe use an external shunt?) and test capacity individually.

 

[Grand Adventure]

What is shutting down (battery or inverter) and what is the error message?
What is the charging voltage? Is current flowing into the battery smoothly during charge right up to 14.2+ volts? This is to verify no battery shut down when charging.
Probably best to separate and test the five batteries individually.

Both shut down on Monday. The inverter shut down moments before the battery bank shut down, too. In today's incident I caught it with the generator after the inverter shut down, but before the battery bank shut down, because I was actually awake this time. LOL.

The charging voltage is 14.4 volts through absorption, then 13.6 volts float, which is Battle Born's recommended settings. Yes, voltage slowly increases consistently and smoothly through the charging process up to ~ 14.0 V, then more rapidly up to 14.4 volts which as I understand it from what I've read, is normal.

By separating and testing the five batteries individually, I presume that you mean charging each one individually with no load, then upon reaching full charge let it rest before checking the battery voltage at the terminals? If so, we did that in July or August when this problem first arose, which is when I removed from the bank the sixth battery which I suspected of a faulty BMS.

 

[Q-Dog]

I would take each battery out of the system individually and charge it to 100% full. Once all are full, put the system back together.

Don't you have a 10 year warranty with Battle Born? If you have one failure you should pursue the warranty.

 

[Grand Adventure]

Sounds like only a couple if your batteries are properly functional, I’d get a clamp-on DC ammeter and ensure all the batteries are charging and discharging around the same rate.

Thanks. We actually did that following the earlier July/August incident, and everything was around the same rate.

And then, because running 5 in parallel is going to be a nightmare, take them out one at a time, fully charge them till balancing is complete (do you have comms or BlueTooth or something?) and test capacity individually.

No comms directly with the batteries themselves, as they're not Bluetooth capable. However, we also did precisely that following the July/August incident. All five presently in the battery bank went through that process (charging individually, then discharging individually). All seemed normal. We've been at campsites with power hookups ever since...until now.

 

[Grand Adventure]

I would take each battery out of the system individually and charge it to 100% full. Once all are full, put the system back together.

Don't you have a 10 year warranty with Battle Born? If you have one failure you should pursue the warranty.

We do. I've reached out to them as well, and I'm awaiting their response.

 

[time2roll]

By separating and testing the five batteries individually, I presume that you mean charging each one individually with no load, then upon reaching full charge let it rest before checking the battery voltage at the terminals? If so, we did that in July or August when this problem first arose, which is when I removed from the bank the sixth battery which I suspected of a faulty BMS.

Yes and then check that they discharge steady down to 11 volts.

The idea is if the battery shuts down charging it may not be seen because the voltage just pops up and all looks good. Especially easy to hide in a group with others acting normal. Same with discharge if one or more are cutting out prematurely it will be somewhat hidden as the voltage rapidly drops at some point.