Battle Born Balancing Confusion

[chulew]

Can someone help me understand why Battle Born batteries in parallel require 30 minutes of absorb per battery and why not 30 min of absorb per parallel string (especially since the whole bank is only accepting a few amps at most during this time)?

Is absorb phase the same as balancing phase?

Also, the manual that came with my batteries over a yea ago (Battle Born Batteries BB5024 Manual) says the above. A more recent manual (Edition.PIM_BB5024Rev018_09062022) instructs , regarding absorb time, “Two batteries in parallel connections require 30 minutes 100ah”. WTF does that imply? Who is writing this shit? Or am I a total idiot?

 

[brb58]

The latter

BTW, it's not 30 minutes per battery...it's 30 minutes for the entire string! The string has to stay above a certain voltage for the passive balance mechanism to work in each battery. If you don't keep it in absorb for 30 minutes and let it float, the voltage will fall below the voltage needed for the BMS to allow passive balance.

Understanding Lithium-Ion: Getting Started with Your Battle Born Batteries

Want to learn more about our lithium-ion batteries? Read about the basics after purchasing Battle Born Batteries for your system.

battlebornbatteries.com

 

[Jims94vmx]

Great question. I also thought it was 30 min per battery, but thought what if I had 10. I only have 2 btw. Didn't make sense but I have been at an hour since I got my 2nd battery. Will change it to 30 minutes. Thanks.

Jim H

 

[RCinFLA]

If the absorb voltage remains high enough, >14.2v, on parallel batteries, it doesn't matter how many parallel batteries are connected.

If charging current is low, the balancing dump current sum for all the parallel batteries may exceed the low charging current rate. This would cause the charge absorb voltage level to drop, possibly causing some of balancing dumps to stop which, in turn, allows absorb voltage to rise again, repeating the cycle over and over until all batteries are balanced. This will likely take longer than 30 minutes if balancing is cycling on and off due to the charge absorb voltage variations.

30 minutes is not a lot of balancing time during absorb voltage. The amount of time required depends on how often you did a full >14.2v charge on batteries. It could require much longer to rebalance all cells if you have not fully charged battery in the last 6 months or more.

Balancing dump is less than 200 mA. 1% state of charge imbalance on 100 AH battery takes >5 hours at absorb voltage to rebalance out the 1 AH SoC imbalance.

Cells have a 0.5% to 4% of C rating per month of self-leakage depending on ambient temp and condition of cells. The variation in cell self-leakage rate can create a 1% state of charge imbalance in a few months of non-use. Using battery at high discharge rates accelerates imbalance rate.

Less than a 1% SoC variance can create a problem with BMS cell overvoltage shutdown of charging when a full charge is attempted. Then you have to add the time to bleed down the one cell causing BMS charging shutdown to get BMS to reset and start further balancing on lower SoC cells which extends the required balancing time.

Some chargers will think battery is fully charged when BMS shuts down charging causing charger to drop to float mode. When this happens, no further balancing will happen after BMS resets charge enable. You have to disconnect and reconnect charger to get it to reinitiate a full absorb level charge. Many chargers will not initiate a full absorb level charge if battery voltage is greater than about 12.6v so the charger may jump directly to float mode voltage when charger is reconnected.

 

[brb58]

Some chargers will think battery is fully charged when BMS shuts down charging causing charger to drop to float mode. When this happens, no further balancing will happen after BMS resets charge enable.

Which is why I bought a 120VAC charger that can be put in power supply mode. I hate converters.

 

[chulew]

The latter

BTW, it's not 30 minutes per battery...it's 30 minutes for the entire string! The string has to stay above a certain voltage for the passive balance mechanism to work in each battery. If you don't keep it in absorb for 30 minutes and let it float, the voltage will fall below the voltage needed for the BMS to allow passive balance.

Understanding Lithium-Ion: Getting Started with Your Battle Born Batteries

Want to learn more about our lithium-ion batteries? Read about the basics after purchasing Battle Born Batteries for your system.

battlebornbatteries.com

My original battery manual states and I quote:
"Bulk/Absorb: 28.4V - 29.2V"
"Absorption Time: 30 min per battery (for parallel string)"

Did they screw up writing the manual? My batteries are all in parallel (6 battery parallel string in parallel with another 6 battery parallel string; 12 batteries all in parallel). 12 x 30min = 6hrs absorb or if they meant 30 min per parallel string = 1 hr. On my first charge cycle it took 6 hrs from Low Batt Cut Off (~23.5V - my conservative setting) until the BMS started clipping the charge current from 100A CC (my max charge current) as it reached 28.8V.

I was instructed by Battle Born Support Tech: "Recommended Absorb Time of 3 hrs for my bank and setup (12 x BB5024 24V batteries in parallel with 100A max charge current). So that is 6 hrs from LBCO to reach absorb timer start (28.8V). Then balancing begins (the move from 27.8V to 28.4V happens fast).

The newer manual says and I quote:
"Bulk/Absorb: 28.4V - 29.2V"
"Absorption Time: Two batteries in parallel connections require 30 min 100Ah."

How do I do an Absorb charge of "30 min 100Ah"?? 30 min @ 100A DC/hr? 100Ah is the total Ah for two BB5024s in parallel. Again, is it me or is this spec is very poorly written? I've never heard of programming an Ah figure into an Absorb Time setting?

Both manuals versions state: "How to Maintain the Batteries: ...If your batteries are in parallel...just make sure the batteries are charged to 28.4V - 29.2V frequently for internal balance." Frequently is relative. And again, Absorb instruction seems convoluted.

 

[chulew]

If the absorb voltage remains high enough, >14.2v, on parallel batteries, it doesn't matter how many parallel batteries are connected.

If charging current is low, the balancing dump current sum for all the parallel batteries may exceed the low charging current rate. This would cause the charge absorb voltage level to drop, possibly causing some of balancing dumps to stop which, in turn, allows absorb voltage to rise again, repeating the cycle over and over until all batteries are balanced. This will likely take longer than 30 minutes if balancing is cycling on and off due to the charge absorb voltage variations.

30 minutes is not a lot of balancing time during absorb voltage. The amount of time required depends on how often you did a full >14.2v charge on batteries. It could require much longer to rebalance all cells if you have not fully charged battery in the last 6 months or more.

Balancing dump is less than 200 mA. 1% state of charge imbalance on 100 AH battery takes >5 hours at absorb voltage to rebalance out the 1 AH SoC imbalance.

Cells have a 0.5% to 4% of C rating per month of self-leakage depending on ambient temp and condition of cells. The variation in cell self-leakage rate can create a 1% state of charge imbalance in a few months of non-use. Using battery at high discharge rates accelerates imbalance rate.

Less than a 1% SoC variance can create a problem with BMS cell overvoltage shutdown of charging when a full charge is attempted. Then you have to add the time to bleed down the one cell causing BMS charging shutdown to get BMS to reset and start further balancing on lower SoC cells which extends the required balancing time.

Some chargers will think battery is fully charged when BMS shuts down charging causing charger to drop to float mode. When this happens, no further balancing will happen after BMS resets charge enable. You have to disconnect and reconnect charger to get it to reinitiate a full absorb level charge. Many chargers will not initiate a full absorb level charge if battery voltage is greater than about 12.6v so the charger may jump directly to float mode voltage when charger is reconnected.

Thank you! This is valuable info ^^^. Right now, I don't have enough sun or solar capacity to end with solar balancing conditions although I hope to have it by this summer.

I think I have noticed the cycling balancing dumps you mentioned. I agree that 30 minutes of absorb time is not a lot. Battle Born tech most recently told me that as long as my charge voltage is programmed to 28.8 V (14.4V), balancing will happen from the start of my charge cycle which is BS since the manual states balancing happens only when V>28.8 and this occurs only after bulk charge (CC mode) raises V enough. I charge 2-3 times per week and only do a balance every 2-4 weeks since it can take 6 hrs to get to balancing voltage and then another 3 hrs (per manual) for absorb (if this is even right).

I have used EQ mode with same 28.8V CV absorb with time setting so as to avoid the charger getting too smart for the bank. I just seem to be getting way to much variation in proper specification from Battle Born (manuals and support people). If the manual can be shown to have changed significantly in its instruction, then I wonder how much fuel I've burned needlessly to adhere to their poorly written instructions (or risk early degradation, even though they are warranteed - I would expect they would attempt to blame the operator for negligence). Does this make sense?

 

[RCinFLA]

Typical fixed setting BMS will start a cell balance dump on each cell when it exceeds 3.40v. There may be some tolerance variation on that number up to +/- 50 mV around 3.4v.

Once a given cell triggers a balance dump at 3.40v you still have to hold the voltage above 3.4v to keep the current dump happening. Typical fixed settings self-contained 12v LFP batteries will have a resistor based balance dump current between 50 mA and 200 mA. You will not likely find a resistor dump balance current above 200 mA due to heat dissipation limit on the dump chip resistor.

For a four cell 12v self contained LFP battery you need to get above 4x 3.45v = 13.8vdc to get some balancing time on all cells. Typical target for absorb voltage is between 3.5v and 3.6v times number of series cells. 3.55v x 4 = 14.2 vdc.

Once balancing starts, it is then a race to get all cells balanced before any single cell reaches BMS overvoltage limit. The greater the BMS balancing dump current the more likely to win the race.

When you have not balanced battery for a few months you are more likely to lose the race, resulting in a BMS cell overvoltage charging shutdown.

If you know you have not balanced for a while and cells are imbalanced, as charger approaches absorb voltage you can back down the charging current rate to allow more balancing time before a cell overvoltage trip happens. Reducing the ratio of charging current to balancing dump current will give you more balancing runway time before hitting a cell overvoltage limit.

 

[brb58]

My original battery manual states and I quote:
"Bulk/Absorb: 28.4V - 29.2V"
"Absorption Time: 30 min per battery (for parallel string)"

Did they screw up writing the manual? My batteries are all in parallel (6 battery parallel string in parallel with another 6 battery parallel string; 12 batteries all in parallel). 12 x 30min = 6hrs absorb or if they meant 30 min per parallel string = 1 hr. On my first charge cycle it took 6 hrs from Low Batt Cut Off (~23.5V - my conservative setting) until the BMS started clipping the charge current from 100A CC (my max charge current) as it reached 28.8V.

I was instructed by Battle Born Support Tech: "Recommended Absorb Time of 3 hrs for my bank and setup (12 x BB5024 24V batteries in parallel with 100A max charge current). So that is 6 hrs from LBCO to reach absorb timer start (28.8V). Then balancing begins (the move from 27.8V to 28.4V happens fast).

The newer manual says and I quote:
"Bulk/Absorb: 28.4V - 29.2V"
"Absorption Time: Two batteries in parallel connections require 30 min 100Ah."

How do I do an Absorb charge of "30 min 100Ah"?? 30 min @ 100A DC/hr? 100Ah is the total Ah for two BB5024s in parallel. Again, is it me or is this spec is very poorly written? I've never heard of programming an Ah figure into an Absorb Time setting?

Both manuals versions state: "How to Maintain the Batteries: ...If your batteries are in parallel...just make sure the batteries are charged to 28.4V - 29.2V frequently for internal balance." Frequently is relative. And again, Absorb instruction seems convoluted.

Post your battery manual that states all of this.

I guess a bit of common sense is needed sometimes to overcome a possible manual misprint. May be the case here. If you look at the link I posted, it definitely isn't what they are saying there. Maybe instead of dwelling on this possible misprint, try not to get your panties in too much of a wad.

 

[chulew]

Here is the original manual available at the time I purchases my batteries as well as an updated manual they provided me in Nov 2023.
I just feel that for the cost consumers are paying for these, their instructions should be precise and not ambiguous or changing over time on the critical issues. This investment cost me over $8k and I want to make sure that should I ever have to call them on the issue of warranty, that I've done everything by the book so that I'm covered. If they change the instructions and then deny a warranty claim, or end up costing me tons of cash over 10+ years for generator balancing time that was not needed, that's no small matter.

 

[RCinFLA]

Holding absorb time requirement depends on how mis-balanced the cells are. Battle Born recommendation is based on a battery that has regular balancing with full charge to 14.2v during regular recharge cycle.

The balancing dump resistor in Battle Born 100 AH battery is only 77 ohms. This is about 45 mA of balancing dump current. Depending on level of bulk charging current, you will start to have BMS cell overvoltage shutdown issues when attempting a full absorb level charge, when the balance in SoC between cells gets exceeds about 1% of capacity between the four cells.


1% of 100 AH battery is 1 AH SoC delta between cells. To get balanced again with only 45 mA of balance dump current requires 1 AH/0.045A balancing dump = 22.2 hours held at 14.2 vdc.

Main issue with self-contained 12v LFP battery with no BT RF monitor link is you are flying blind, not really knowing the difference in cell voltage. Only indication of mis-balancing is when you get a BMS cell overvoltage charging shutdown when attempting a full absorb voltage level charge, and you detect less extractable capacity from battery due to cell imbalance. If balance gets bad enough for you to notice less extractable capacity you are really imbalanced, maybe as much as 5 or 6% off in cell SoC balance. This can take a week to get back in balance.

Using battery at high discharge current accelerates cell misbalancing. Running high discharge rates and not fully charging battery will get you in trouble quickly.

 

[chulew]

Holding absorb time requirement depends on how mis-balanced the cells are. Battle Born recommendation is based on a battery that has regular balancing with full charge to 14.2v during regular recharge cycle.

The balancing dump resistor in Battle Born 100 AH battery is only 77 ohms. This is about 45 mA of balancing dump current. Depending on level of bulk charging current, you will start to have BMS cell overvoltage shutdown issues when attempting a full absorb level charge, when the balance in SoC between cells gets exceeds about 1% of capacity between the four cells.
View attachment 140347

1% of 100 AH battery is 1 AH SoC delta between cells. To get balanced again with only 45 mA of balance dump current requires 1 AH/0.045A balancing dump = 22.2 hours held at 14.2 vdc.

Main issue with self-contained 12v LFP battery with no BT RF monitor link is you are flying blind, not really knowing the difference in cell voltage. Only indication of mis-balancing is when you get a BMS cell overvoltage charging shutdown when attempting a full absorb voltage level charge, and you detect less extractable capacity from battery due to cell imbalance. If balance gets bad enough for you to notice less extractable capacity you are really imbalanced, maybe as much as 5 or 6% off in cell SoC balance. This can take a week to get back in balance.

Using battery at high discharge current accelerates cell misbalancing. Running high discharge rates and not fully charging battery will get you in trouble quickly.

So, I'm full off-grid with generator and some solar with a 1.67C max charge rate capability. My bank is all 24V parallel batteries (2 strings of 6). I very rarely run heavy loads. I think this makes me fairly low-risk for getting out of balance.

Are you saying that no matter what, I should be able to re-balance with an extended absorb and that it could take a week-long charge if it is bad enough?

 

[chulew]

Below are all the Battle Born email answers to my repeated inquiries following my purchase about setting up my bank and programming absorb time and balancing correctly. I know I've not hurt the batteries but it has cost quite a bit in fuel for the generator to carry out needless extended absorb times. Even the BB CEO in the link above with the video about how long to absorb for balancing as well as the original BB5024 manual (which is more clear-ish in the latest manual) contradicts all of these emails. Should they really be recommending these long absorb times for a new parallel bank which will likely stay in balance based on my usage (which I explained each time I called)?

12/13/21 BB5024 Battery Manual
"How to Properly Charge the Batteries: Absorption Time: 30 minutes per battery (for parallel string)"

I have two strings of 6 batteries (12 batteries, everything is in parallel, 2 parallel strings). So in reading this, 12 x 30min = 6hrs absorb.
It does not say 30 minutes per parallel string, but if that was the implied instruction, since I have two strings, 30 min per string = 60 min. If it just means 30 minutes for all batteries in parallel, then I would understand absorb = 30 min for my whole system.

1/4/22 Aaron Birchfield "Recommend 30 min absorb time per battery with a max absorb time of 3 hrs. Set to absorb to 3 hrs and good to go."

1/5/22 Aaron Birchfield "For 12 batteries in parallel and 100A charger, empty to full charge would take 6-9 hrs. 600AH/100A = 6hrs + 3hrs of absorption."

1/7/22 Aaron Birchfield "Bank >6 batteries, absorb time of 6 hrs is enough to balance a large bank of batteries via the BMS. Do this once per week."

1/18/22 Mason Bondi "ME-ARC Settings: …CV Charge Done Time = 20 to 30 min per battery so 12/2=6hrs"

1/18/22 Mason Bondi "Once a week recommended absorb interval."

9/6/22 BB5024 Battery Manual
"How to Properly Charge the Batteries: Absorption Time: Two batteries in parallel connections require 30 minutes 100Ah

Video: FAQ: How long do I need to absorb the batteries?
CEO: "You don't need to absorb the batteries but you need to sit in the absorption stage to allow the batteries to balance.
Now typically we recommend about 15-20 min per battery string in parallel.
What that means is that if you have two batteries in parallel, you probably want to sit at an absorption voltage for around 15-30 min.
Also if you have a 24V system, and you have a total of four batteries, two sets of two batteries, then it would be about the same, 15-30 min per battery string. If you have a 48V system and four batteries, that's only one battery string, so we recommend around 15-20 min for absorption.
If batteries are out of balance (if they are cutting off at high voltage sooner than you think), then you can spend longer at the absorption voltage. "

 

[RCinFLA]

I very rarely run heavy loads. I think this makes me fairly low-risk for getting out of balance.

You always have self-discharge rate which is often slightly different rates between cells, not related to typical cell matching criteria.

Self-discharge rate runs from about 0.3% to 3% of cell capacity per month. It is greater at higher cell ambient temperature. It would not be unusual to get up to a 0.5% to 1% per month difference in cell capacity self-discharge rate between series connected cells. 1% difference in SoC between series cells is enough to start to have BMS cell over-voltage shutdowns when attempting a full absorb level charge.

 

[chulew]

You always have self-discharge rate which is often slightly different rates between cells, not related to typical cell matching criteria.

Self-discharge rate runs from about 0.3% to 3% of cell capacity per month. It is greater at higher cell ambient temperature. It would not be unusual to get up to a 0.5% to 1% per month difference in cell capacity self-discharge rate between series connected cells. 1% difference in SoC between series cells is enough to start to have BMS cell over-voltage shutdowns when attempting a full absorb level charge.

So are you saying that the 3hr balance time IS reasonable for a regularly cycled, bank? I assume a reasonable gauge be to check for the rated Ah out of the bank at LBCO after a full charge/balance cycle?

Sounds like it is better to absorb at a voltage closer to the BMS balance voltage of 14.2/28.4 than say 14.6/29.2?

 

[CptPat]

My original battery manual states and I quote:
"Bulk/Absorb: 28.4V - 29.2V"
"Absorption Time: 30 min per battery (for parallel string)"

Did they screw up writing the manual? My batteries are all in parallel (6 battery parallel string in parallel with another 6 battery parallel string; 12 batteries all in parallel). 12 x 30min = 6hrs absorb or if they meant 30 min per parallel string = 1 hr. On my first charge cycle it took 6 hrs from Low Batt Cut Off (~23.5V - my conservative setting) until the BMS started clipping the charge current from 100A CC (my max charge current) as it reached 28.8V.

I was instructed by Battle Born Support Tech: "Recommended Absorb Time of 3 hrs for my bank and setup (12 x BB5024 24V batteries in parallel with 100A max charge current). So that is 6 hrs from LBCO to reach absorb timer start (28.8V). Then balancing begins (the move from 27.8V to 28.4V happens fast).

The newer manual says and I quote:
"Bulk/Absorb: 28.4V - 29.2V"
"Absorption Time: Two batteries in parallel connections require 30 min 100Ah."

How do I do an Absorb charge of "30 min 100Ah"?? 30 min @ 100A DC/hr? 100Ah is the total Ah for two BB5024s in parallel. Again, is it me or is this spec is very poorly written? I've never heard of programming an Ah figure into an Absorb Time setting?

Both manuals versions state: "How to Maintain the Batteries: ...If your batteries are in parallel...just make sure the batteries are charged to 28.4V - 29.2V frequently for internal balance." Frequently is relative. And again, Absorb instruction seems convoluted.

> Did they screw up writing the manual?

Yes.

 

[CptPat]

Something BB also fails to mention is the importance of charge termination detection. Charging a single 100 AH battery to 14.2 volts (3.55 volts per cell group - assuming perfect cell balance) should be halted when the charge current declines to about 3 amps (in a parallel battery group, multiply 3 amps X the number of 100 AH batteries). Charging beyond that point gains only an infinitesimal increase in SOC and contributes to rapid cell degradation. I cringe when I read instructions to continue charging after the charge current has declined to zero. That is abusive overcharging of LiFePO4 batteries! There is an excellent explanation of this topic here:

Charging Marine Lithium Battery Banks​

I charge my 300 AH of BB batteries to a terminal voltage of 14.0 volts (3.5 volts per cell group), and I terminate charging when the "tail" current drops to 9 amps. With that setting, each of my batteries charge to a measured 100 AH. The charge termination setting results in a 14.0 volt terminal voltage being sustained (absorbed) for only a few minutes, but the rise in terminal voltage is very gradual (I'm not in a hurry) because I am charging at only 25 amps (< 0.1C). So far, I've had no issues with that regimen after two years. Cell balancing still seems to occur (despite BB's instructions) at voltages lower than 14.2 volts. It would be nice to know what the actual balancing voltage threshold is. If anyone knows, please advise.

I am using a Victron Smart IP43 Charger that permits setting a tail current for charge termination. I advise against using any charger that cannot terminate charging at a set tail current. Attached is an example of my charge profile (taken from Victron VRM).

 

[RCinFLA]

So are you saying that the 3hr balance time IS reasonable for a regularly cycled, bank? I assume a reasonable gauge be to check for the rated Ah out of the bank at LBCO after a full charge/balance cycle?

Sounds like it is better to absorb at a voltage closer to the BMS balance voltage of 14.2/28.4 than say 14.6/29.2?

No, one or two hours is enough if you keep up on regular balancing. Many users do not.

Many self-contained 12v LFP users do not provide enough balancing time at absorb level. Failure to do this is cumulative and grows delta in SoC between cells. At about 1% SoC difference, depending on charging current, you will start to have overvoltage cell shutdown of charging when attempting full charging. BMS does not balance until a cell exceeds 3.4v.

Battleborn is about 50-80mA balancing bleed dump current. 1% out of balance on 100 AH battery is 1 AH. 1AH/0.05A takes 20 hours above 13.8v to correct imbalance in SoC.

It can take a week if cells are significantly out of balance due to no or insufficient balancing time.

Two common reasons for imbalance. Battery sits idle for months with cell variance in self-discharge leakage rate. High current discharge and charging also accelerates cell imbalance.

 

[sunshine_eggo]

FWIW, BB indicates 14.2V is needed for balancing.

This guy's BB lost nearly 50% capacity in 3 years by never being fully charged:

3 year Battle Born Capacity issue

Looks like i have a problem with my Battle Born batteries. After 3 years having 2 (BB10012) in parallel in my RV, i started to expand my solar on the roof and do a capacity test on my 2 Battle Born batteries. I was pretty shocked to find one was down to 52.4 amps (653wh) and the other one at 87...

diysolarforum.com

Here's the post indicating near full recovery after 1 week @ 14.2V:

3 year Battle Born Capacity issue

After 30 hours at 14.1v it tested at 58ah 7ah higher than the first run. So now I have it back on the power supply at 14.1 again. How does it respond at 14.2? Does it still disconnect there?

diysolarforum.com

EDIT: Given that rate of recovery, it would seem that BB balancers are >80mA?

 

[sunshine_eggo]

I am using a Victron Smart IP43 Charger that permits setting a tail current for charge termination. I advise against using any charger that cannot terminate charging at a set tail current. Attached is an example of my charge profile (taken from Victron VRM).

This is not bad advice, but LFP can be a little wonky (especially with DIY batteries), and fixed absorption times at lower voltages WITHOUT tail current may be necessary to ensure sufficient time at elevated voltage is attained for balancing.

Given that few folks can charge their batteries @ the typical rated 0.5-1.0C rate, absorption voltage is attained later and at a higher state of charge, thus tail current may cut off charging after only 5 minutes @ absorption voltage. 5 minutes/day daily may be sufficient. Victron indicates their LFP batteries must attain absorption voltage for at least 2 hours per month. If charging to a lower voltage like 3.45V/cell, 30-120 minutes may be needed to attain ~98% SoC.

The length of absorption and use of tail current is battery/system specific. If regularly monitoring cell voltages with consistent dV @ charge termination, then it is fine. If dV trends get consistently larger, tail current may need to be disabled with a fixed absorption period applied to enable more time for balancing.