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I'm looking for a battery balancer for 2x 24V lifepo4, 48V system.

whatismouse

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Oct 11, 2020
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My two bigbattery 24V batteries are terribly out of balance. Its not a question of just putting them in parallel every once in a while, because the same battery goes higher V on the top and lower V on the bottom. (currently about 1.5V at the top, and 3V difference at the bottom, with conservative parameters).

I need a battery balancer that keeps them the same voltage, at every SOC. Does anyone know of any that will keep two 24V batteries in balance?
 
ok since no one replied I'm going to assume they don't exist, which is kind of what I figured.

however the other solution I thought of would be to get a 16S BMS and treat my two batteries like one.
 
I'm not sure what your asking? but maybe you are looking for something like a hel tec active balancer...
US $6.79 15%OFF | 5A 5.5A Active Equalizer Balancer Lifepo4 / Lipo/ LTO Battery Energy equalization Capacitor 3S 4S 5S 6S 7S 8S 14S 16S 20S 24S
 
I'm not sure what your asking? but maybe you are looking for something like a hel tec active balancer...
US $6.79 15%OFF | 5A 5.5A Active Equalizer Balancer Lifepo4 / Lipo/ LTO Battery Energy equalization Capacitor 3S 4S 5S 6S 7S 8S 14S 16S 20S 24S
These are for small batteries. If you look at the voltage range its something like 1.5v to 4v.

I'm talking of having a balancer with a working voltage range for that of a 24v battery. I've got 2 24v batteries connected in series to a 48v bank. When the inverter finish charging them there is a voltage difference of up to 0.5v and when they are discharged the difference can get up to 4v. I'm looking for a balancer that will always ensure that the difference AT ANY POINT is less that 0.1v
 
Cell Balancing within a Battery Pack is one thing, Balancing between packs is another thing.

Cell balancing will only keep cells within a single pack closer together BUT no balancer can fix or compensate for poor/weak cells.
Passive Balancing only burns off Hi Volts from Hi Cells.
Active Balancing can transfer Hi Volts to Lo Volt cells within the same battery pack.
Packs will and do behave independently and some minor deviation between them is not unusual. Most often some of this can be attributed to the installation, every lug, fuse, terminal etc adds resistence and as such contribute to Voltage & Amperage drops.

NOTE !
Voltage Differential (OffSet) will always be different during Charge VS Discharge this is just the way it is.
Charger Devices (SCC, External Charger or Inverter/Charger (if used for charging) need to be corrected so they charge to the ACTUAL points desired on the battery packs, so that you do not over/undershoot.
DISCHARGE Devices like the Inverter (if not used for charging) must be corrected so that the Values are matched to the battery pack states during Discharge otherwise your 40,0V Cutoff (2,50Vpc) could be lower & causing damage.

FYI: LFP in series is not generally recommended and is more oriented to serve the "Drop-In Replacement" crowd more or less. There are several issues doing so. This is why the Standing Recommendation is to build & buy a Battery Pack assembly for your Target Voltage, be it 12,24,48 or higher.

ON BALANCERS, I have used many & tested several. They are NOT EQUAL and some are downright junk and others are very specific to the exact chemistry. I have used QNBBM-8S Active Balancers on my 8S Packs and these do exactly as stated and quite well at that as well. BUT I am now changing my entire fleet of BMS' (production & utility packs) to JKBMS' with 2A Active Balancers BlueTooth/CanBus/RS485. My current fleet includes 6x Chargery BMS8T with 300A Solid State Contactors and QNBBM Active Balancers, JK-BMS & JBD-Bms' with add-on HelTec Capacitive Balancers representing a couple of grand worth of gear to go into the used parts bin.
 
Cell Balancing within a Battery Pack is one thing, Balancing between packs is another thing.

Cell balancing will only keep cells within a single pack closer together BUT no balancer can fix or compensate for poor/weak cells.
Passive Balancing only burns off Hi Volts from Hi Cells.
Active Balancing can transfer Hi Volts to Lo Volt cells within the same battery pack.
Packs will and do behave independently and some minor deviation between them is not unusual. Most often some of this can be attributed to the installation, every lug, fuse, terminal etc adds resistence and as such contribute to Voltage & Amperage drops.

NOTE !
Voltage Differential (OffSet) will always be different during Charge VS Discharge this is just the way it is.
Charger Devices (SCC, External Charger or Inverter/Charger (if used for charging) need to be corrected so they charge to the ACTUAL points desired on the battery packs, so that you do not over/undershoot.
DISCHARGE Devices like the Inverter (if not used for charging) must be corrected so that the Values are matched to the battery pack states during Discharge otherwise your 40,0V Cutoff (2,50Vpc) could be lower & causing damage.

FYI: LFP in series is not generally recommended and is more oriented to serve the "Drop-In Replacement" crowd more or less. There are several issues doing so. This is why the Standing Recommendation is to build & buy a Battery Pack assembly for your Target Voltage, be it 12,24,48 or higher.

ON BALANCERS, I have used many & tested several. They are NOT EQUAL and some are downright junk and others are very specific to the exact chemistry. I have used QNBBM-8S Active Balancers on my 8S Packs and these do exactly as stated and quite well at that as well. BUT I am now changing my entire fleet of BMS' (production & utility packs) to JKBMS' with 2A Active Balancers BlueTooth/CanBus/RS485. My current fleet includes 6x Chargery BMS8T with 300A Solid State Contactors and QNBBM Active Balancers, JK-BMS & JBD-Bms' with add-on HelTec Capacitive Balancers representing a couple of grand worth of gear to go into the used parts bin.
The bolded is my current case.
For now its not possible to not run them without connecting in series. I'm still negotiating with the battery supplier for a single 48v battery as my inverter is 48v.
Since that's the case for me right now, how do I maintain the SOC between packs? Each back is 24v.
 
FYI: LFP in series is not generally recommended and is more oriented to serve the "Drop-In Replacement" crowd more or less. There are several issues doing so. This is why the Standing Recommendation is to build & buy a Battery Pack assembly for your Target Voltage, be it 12,24,48 or higher.
Just to add a data point - I have two SOK 12V 206Ah batteries in series for my 24V system. I received them just under a year ago before SOK had their 24V battery available. My two LiFePO₄ batteries have been in series for about 7 months now and 99.6% of the time they are at the exact same voltage. My system monitors both 24/7 so I am alerted if the voltage difference between the two gets beyond 0.15V. The only time they get even slightly different voltage is when fully charging to 28.4V via solar. When it gets to the absorption stage the batteries will be different by up to about 0.12V. Once the absorption stage ends (15 minutes) the battery voltages slowly go back to being exactly the same in about 30 minutes. At all other times the voltages are always the same.

Before initially putting the two batteries in series I first fully charged both batteries, one at a time, using a 12V charger. I then connected the two in parallel and fully charged them again and left the 12V charger on overnight. This was with a LiFePO₄ friendly charger. I then disconnected the charger and left the two batteries in parallel for half a day to really be sure they were at the same SOC. Then I finally put them in series and they have been that way since.

My point is that with proper prep it is possible for at least some LiFePO₄ batteries to be put in series without any problems.

Having said all of that, I would have bought 24V batteries for my 24V system if they had been available at the time.
 
I Agree with RMaddy with respect to SOK but we know that one version to the next of BigBatt could be different, even within the same batch. There is a lot of experience with those "quirks" around here but that's the nature of that beast (previously enjoyed cells), going back to the BYD shtick. glad I dodged that one...
 
There are lots of 12V balancing series options. Certainly it's possible to create a 24v series to 48v balancer.

24v batteries work really well with my panel voltages and generally are much lighter (under 50lbs).
48v batteries are required for half my needs, 24 for the other half.

if only I could use 24v everywhere and balance as needed :(
 
One idea that might be okay but it only works with Lifepo4.

Lifepo4:
24 = 8sXp
Setup my 24v battery normal 8s and then however many cells in parallel.

Then add 1 additional wire on the battery leading to the 4th cell (the 12v cell).

Then get a 12v -> 48 volt balancer which has 4 leads.
- Battery 1 -
12v Battery 1 4th cell
24v Battery 1 +
36v Battery 2 4th cell
48v Battery 2 +

The 24v battery bms should only help when the 48 v device is working on the cells.

For Lipo... I'm stuck, any ideas?
 
Lipo idea!!!

This idea would require an Lifepo4 battery:
48V / 12v Balancerlifepo4 (cell connection)Lipo (cell connection)
0v
0​
0​
12v
4​
24v
8​
7​
36v
12​
48v
16​
14​

Lots of different ways to actually assemble this safely.
Simplest to explain: Balance 4 24v batteries. 2 lifepo4, 2 lipo.
Then connect as shown above. With big batteries I'd propose using resisters to hook up the wires first to let the voltages flow if needed. You could use these if you don't want to wait long.

The stand alone 24v pack BMS should take care of all the internal cells.
With the extra capacity the range of charge and discharge could limited for greater cell health.

Thoughts?
 
These are for small batteries. If you look at the voltage range its something like 1.5v to 4v.

I'm talking of having a balancer with a working voltage range for that of a 24v battery. I've got 2 24v batteries connected in series to a 48v bank. When the inverter finish charging them there is a voltage difference of up to 0.5v and when they are discharged the difference can get up to 4v. I'm looking for a balancer that will always ensure that the difference AT ANY POINT is less that 0.1v
Ever figure it out? I'm set with 2x24 LifePO4 batteries (48v system)?
 
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