Is an active balancer needed for 16s battery bank?

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Mar 7, 2022
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Hi everyone,

I've been viewing a number videos on active balancers. I'm still unable to make up my mind conclusively whether an active balancer should be included in the setup, along with a BMS. My batteries are new but haven't arrived yet. So I'm not able to check their voltages, etc.
Thought of asking you all what's the best thing to do, in case if i do need an active balancer, I'll try to purchase them ahead. Thanks for clearing my confusion/doubts about LFP active balancer once and for all !
 

RCinFLA

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The more balancing current the better but stay with balancing only above 3.4v per cell. Balance degrades faster with cell aging, high charge/discharge currents on cells, and higher ambient temps. The more mis-matched the cells the faster they will diverge in SOC balance.

The JK BMS with active balancer or JK active balancers allow cell start of balancing voltage to be user set.

Stay away from any active balancer that balances all the time throughout the whole state of charge range of battery unless maybe you are totally PV supplied off grid and seldom able to achieve a full recharge.
 

Britguy

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Stay away from any active balancer that balances all the time throughout the whole state of charge range of battery unless maybe you are totally PV supplied off grid and seldom able to achieve a full recharge.
Would completely disagree,
I use cheap second hand batteries and they go out of balance at the top (limiting the BMS charge by high cell charge cutoff), and at the bottom (limiting the BMS discharge with low cell voltage cutoff).

So I stack the 8 high/low batteries together (alternating high with low) and an 8 cell capacitive balancer, then the 8 medium batteries are stacked with no balance (saves me $30 by buying an 8 cell balancer in place of a 16 cell balancer) to give me my 16 cell 48V battery pack.
 
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RCinFLA

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The main issue with balancing throughout the flat portion of battery curve is with moderate amounts of variable inverter load current, slight variations in cell internal impedance and variance in cell terminals connection resistance, will cause variable apparent cell voltage at the balancer.

You can easily get 10-30 mV delta with 100A discharge current, even with well-matched cells. The more mismatch between cells the worse the delta.

This causes balancer to randomly make the wrong balancing direction decision.
 
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toms

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The only issue with fitting an active balancer is the reliability.

You certainly don’t need one, i prefer a BMS that can control current while passive balancing.
 
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Hey everyone, thanks for all the feedback! There are new terms which i need to look up. Still learning as i go along this solar journey. Appreciate your time, advice and personal opinions. Every bit means a lot to me, as a beginner 😃👍
 

newbostonconst

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The main issue with balancing throughout the flat portion of battery curve is with moderate amounts of variable inverter load current, slight variations in cell internal impedance and variance in cell terminals connection resistance, will cause variable apparent cell voltage at the balancer.

You can easily get 10-30 mV delta with 100A discharge current, even with well-matched cells. The more mismatch between cells the worse the delta.

This causes balancer to randomly make the wrong balancing direction decision.
The only issue in your thought process is that the closer that each cell is in voltage then less energy is moved.
 

Britguy

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You can easily get 10-30 mV delta with 100A discharge current, even with well-matched cells. The more mismatch between cells the worse the delta.
My 5A capacitive active balancer would take a week to move 30mV.
 

Capt Bill

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The more balancing current the better but stay with balancing only above 3.4v per cell. Balance degrades faster with cell aging, high charge/discharge currents on cells, and higher ambient temps. The more mis-matched the cells the faster they will diverge in SOC balance.

The JK BMS with active balancer or JK active balancers allow cell start of balancing voltage to be user set.

Stay away from any active balancer that balances all the time throughout the whole state of charge range of battery unless maybe you are totally PV supplied off grid and seldom able to achieve a full recharge.
Re: My recently delivered 8S Heltec 5A active balancer: I am wondering; on my 8 x 280Ah below par LifePO4 cells; ... What is, or Would be the Advantage; ... if I wired the balancer through an automated controller that would allow connection to my 280Ah cells, ONLY at the higher >3.3v or > 3.4 Cell volt range? I have a $30 controller way in mind I could use to automate the Heltec to turn ON at >27.0v on my 8 cell battery pack / and off <26.0 volts. ... I would be using the Heltec Active Balancer along side my Chargery BMS8T that has just resistance balance I currently have configured to go on at >3.4 volts... in charge and discharge modes. ... I am seeking opinions as to my better option, plus any pertinent reference info.
 
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ocular

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I support your attempt to limit your active balancer to balance at greater than 3.4V. Think of it as a system top balance. The deviations of cell voltage in the flat of the curve is not due to cells out of balance but due to current in/out fluctuations. If the active balancer is working in the flat of the curve it reacts to the current fluctuations and creates more work for top balancing.The JkBMS with integrated active balancer can be set to do this- the unit detects when any any cell voltage hits 3.4V (adjustable), but the JK standalone active balancer, does not have this feature. The Neely 4A active balancer (Generation 3) now has an adjustable on/off voltage that I think is one particular cell. So that may no be ideal if that cell is low in the balance range. Your concept of using a total pack voltage may not precisely represent cell voltage but should work especially if the pack is relatively balanced. If there is a large delta V(100-200mV) then leaving the active balancer on all would be advised initially. Another concept in some predictable OffGrid systems would be to switch on balancer say from 12-3pm when full charge is happening. This is likely to keep a well balanced system in check.
 
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madmax

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I use a 7s balaencer... And it seems to do just fine working with a bms. On a cycle it will come on here and there, but it is way less than when I first installed it. Plus I like the little led indicator lights. I don't think I'm hurting too much of anything, and it lets me not have to kick in the 4.2v per cell to top balance. The question is which does more harm. Topping off and staying at 4.2v or to allow an active balance to work at like 3.7
 

Visusolar

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Re: My recently delivered 8S Heltec 5A active balancer: I am wondering; on my 8 x 280Ah below par LifePO4 cells; ... What is, or Would be the Advantage; ... if I wired the balancer through an automated controller that would allow connection to my 280Ah cells, ONLY at the higher >3.3v or > 3.4 Cell volt range? I have a $30 controller way in mind I could use to automate the Heltec to turn ON at >27.0v on my 8 cell battery pack / and off <26.0 volts. ... I would be using the Heltec Active Balancer along side my Chargery BMS8T that has just resistance balance I currently have configured to go on at >3.4 volts... in charge and discharge modes. ... I am seeking opinions as to my better option, plus any pertinent reference info.
Hi
Have you already attempted to control your active balancer through a controller? How did it go? You may share your experience also in this thread or get some inspiration in case you haven't attempted not yet. There we also look for ways to make these active balancers smarter.
 

Capt Bill

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Hi
Have you already attempted to control your active balancer through a controller? How did it go? You may share your experience also in this thread or get some inspiration in case you haven't attempted not yet. There we also look for ways to make these active balancers smarter.
moving slow on my Heltec active balancer testing / planning to test for ON @ >3.35v or >3.4v / ... including with reset of bulk charge from 28.2v to 29.0v ... to see what happens at a later date. I want to see if a change from my Chargery BMS's 1.2A passive balancer to this active balancer will keep my top charge cell v profiles balanced at a full charge to 29.0v (on my 8 x 280Ah x 2 battery banks w aged cells). Currently my higher cell v balance profiles are in the OK zone with my Chargery BMS8T(s), when my Bulk Voltage Charging adjusted to 28.2v (about highest I can get without a BMS trigger). ... I did solder wires to my Heltec for the off and on option. I have a couple of inexpensive controller options to work with that monitor total battery voltage (... so cell volts will be estimated). Other projects are ahead of this one, including fabricating a battery rack to stack on top of my first one, and then integrating my 3rd 24v 280Ah battery bank to my first two.
 
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Samcat

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I would advise to be little sharper curve for active balancer 3.455 per cell. A lot easier to bring lifepo4 chemistry to the tight mV difference. And make sure you calibrate active balancer to stay away from flat curve of lifepo4. Bottom or top balance you choose the flavor. Each has some things to be prepared for when deciding with what you will go.
And only going lower from 3.455 if you have well behaving battery bank.
 
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