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JK BMS - When does it trigger the balancing?

globichen

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Nov 4, 2022
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What is the exact criteria for the active balancer to be triggered inside the JK BMS (I guess any model?) ?
Assuming I set the balancer activation to 3.45V, what will happen when:

- only one cell is above 3.45V, the rest is still below. Will it balance anything?
- a few cells are above, a few are below 3.45V. Will is balance only those cells that are above 3.45V or also the ones below?

The other day I noticed that when I charged my 16s pack, they all were at around 3.35V, then 15 of them shot up beyond 3.45V almost instantly, leaving one cell at the 3.35V level and it had a hard time catching up.

Hence me now wondering when and what gets balanced and under which scenarios.
 
* They will start to balance per the setting on the Settings Page. (Start Balance Voltage) NB: I start Balancing at 3.37 Volts.
* The threshold is also set on the settings page, usually when there is a 0.010 V difference (default). (Balance Trigger Voltage)
* Only cells which exceed the delta will be balanced, even if only 1 cell is above the threshold.

When observing the main screen, you will see a cell voltage in Blue (High Cell) "Blink" which is taking the voltage difference and the Red (Low Cell) "Blink" as it is getting charge balance, the Balance Current on the main screen displays a -### and when taking in charge then when transfering the charge it will be positive.
 
As per @Steve_S balancing starts when any cell voltage passes the default "Start Balance Voltage" 3.37V (adjustable) and the voltage difference is greater than default 10mV (adjustable). What you were seeing was a function of the overall charging voltage and what happens as each cell approaches their 100% SOC. In the situation you describe the balancer was above the threshold >10mV delta V and any cell > greater than 3.37V.
Any imbalance only begins to be unmasked as the pack is pushed to it's full state of charge. In general take note of the delta V from 55V onwards. Interpreting delta V below this pack voltage is meaningless. Then push to 56V pack voltage and any imbalance will be unmasked and voltages will diverge and if delta V is < 20mV everything is in order. A 200mV difference at this level could mean as much as 20-30% difference in cell SOC and will take a long time for 2A active balancer to correct. As long as you push the pack to this level regularly the active balancer will easily cope with balancing. If you only charge to 54V then you may allow imbalance to regularly accumulate without giving the active balancer a chance to work.
 
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