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diy solar

DIY 24v Battery - do I need to balance cells?

Initial parameters
BMS : OV cell protec : 3. 65 (datasheet) / OV batt protec : 28.4V
Solar CHARGER : absorption 28.4V and float voltage 27V.
When the solar switches from bulk to absorption, the cells start to unbalance. So, I decided to unpack the battery to do a balance. I don't think that is a top balance as every single cell was not fully charge. After this balance, each cell was at 3. 41V.

You said you balanced them. How did you balance them?
 
If your bms can't bring the cells into syncronization at charge voltage.
Then you should top balance using one of the more aggressive methods.
Do you think that this kind of balancer can be usefull during the charge and can be a better balancer than the one included into the BMS ?
Does it make sens (and isn't it "dangourous") to connect both BMS and balancer ?
 
This is not a top balance...You should connect all cells in parallel and charge the pack to 3.65V all together. Once current drops below a certain amount, this means your cells are balanced...
You could have all cells at the same voltage, but with still current flowing from one to the other.
THis is the only way to be sure the cells are 100% charged.

Ce n'est pas un "Top Balance". Il faut que tu branches en parallèle et que tu charges le pack à 3,65V. Une fois que l'intensité diminue sous une valeur faible, celà veut dire que les cellules sont équilibrées.
EN branchant en parallèle, sans charger, tu peux avoir les cellules à la même tension mais avec encore du courant qui passe de l'une à l'autre.
C'est la seule façon d'être sure que les cellules sont chargées à 100%.
 
I know of only TWO Good Active BMS makers at this time. Heltec & QNBBM
You are showing one version of the Heltec Balancers, they have several models with various features & amp capacity.

TBH, You are better off dealing directly with Heltec. Here is the link to their store / active balancers.

Deligreens QNBBM family is here:

Some BMS' have Passive Balancing which is semi moot with large capacity cells because A) it's very slow & B) it only burns off high voltage from hi cells. A few BMS (Heltec makes some) have Active Balancing which transfers power from Hi to Lo cells but often the ones with BMS are not High Amp.

NO BALANCER can fix poor, weak or damaged cells. Balancing (passive or active) works best with Matched, Batched & Binned cells. The common Commodity Cells we use for ESS that are sold by the vendors to us are NOT Matched/Batched or binned. That costs a LOT because it is time-consuming & laborious and can easily add $50 to each cell cost.

REF:
BU-803a: Cell Matching and Balancing – Battery University
Li-Ion BMS - White Paper - Dissipative vs. nondissipative balancing (a.k.a.: Passive vs. Active balancing)
Pre-Balancing Cells | Orion Li-Ion Battery Management System
 
Shouldn't the Batrium BMSs' be included in that list? WatchMon4 is able to balance 28.8Ah per cell per day.
 
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