Balancing Lifepo4's, active or passive balancing?

[sailingchiro]

I have two sets of Lifepo4's on our boat. One set only has the BMS to balance the cells and over time and use, they get over 200mV off.
The other set has the BMS AND an ACTIVE capacitor balancer from Heltec.

The second set with the active balancer will balance within 5mV in 2 hours after full charge. It works very fast when compared to the BMS. My active balancer can move up to 5 amps to a low cell. The BMS will only move 200mA. I have let my BMS only batteries set for a month and they are still over 200mV off. And yes, I have performed a top balance.

If I am getting such good results from active balancing, why is it discouraged? Do the capacitors interfere with systems on the boat? I haven't noticed any problems. I am currently considering active balancing on the other Lifepo4's unless I persuasive reasons not too.

[T1 Terry]

We use these cell balancers for 8S (24v) and 16S (48v) There are a lot of mobs selling these cell equalisers out there so best to shop around, but this will give you the general idea if what brand they are .https://www.aliexpress.com/item/1005...ou_100511348.1 and
https://www.aliexpress.com/item/1005...47977576%22%7D for the 16 cell batteries.
The system only sees any cells in parallel as a single cell, but if you had 2 x 4 cell 12v batteries in parallel, if an 8 cell equaliser was used then cell 1 from battery one would be the first red and black cable, cell 1 on battery two would be the second red and black cable and so on. These things are very good at shifting capacity from any high voltage cell to the lower voltage cells resulting in a very fast balance.
The down side is they can mask a faulty cell until it really drops its bundle. Ideally these balancers wouldn't activate until a cell voltage of 3.6v was seen on any cell and turn off when the differential was less than 10mV, but as far as I can tell, such a device hasn't been built yet.

T1 Terry

[goboatingnow]

Originally Posted by sailingchiro

I have two sets of Lifepo4's on our boat. One set only has the BMS to balance the cells and over time and use, they get over 200mV off.

The other set has the BMS AND an ACTIVE capacitor balancer from Heltec.



The second set with the active balancer will balance within 5mV in 2 hours after full charge. It works very fast when compared to the BMS. My active balancer can move up to 5 amps to a low cell. The BMS will only move 200mA. I have let my BMS only batteries set for a month and they are still over 200mV off. And yes, I have performed a top balance.



If I am getting such good results from active balancing, why is it discouraged? Do the capacitors interfere with systems on the boat? I haven't noticed any problems. I am currently considering active balancing on the other Lifepo4's unless I persuasive reasons not too.

Do you actually find a need to balance on normal day to day usage. What sort of stats on balancing are you keeping.

Active balancing seems to mean different things. To me as an EE active means using dc dc converters to shift charge from cell to cell , ie the energy Isnt lost as heat. whereas passive means using resistive elements only and the energy is lost.