| Feb 16, 2021, 10:56 AM (21 hours ago)
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Peter,
Sorry but you can not use voltage as an indication for SOC with LiFePO4 not even a rough estimation. The only thing voltage can be used is to say if battery is full or empty and nothing in between.
I think you refer to the graph below that I shown a few times on the forum. You can have the battery at 90% or at 30% SOC and see the same battery voltage (so it will be completely useless to try and guess the SOC).
Answering the question of the charge/discharge rate in that graph will be fairly mining less unless you also know the capacity and internal resistance of the cells (cell resistance also fluctuates significantly with temperature).
The top point on SBMS0 is 3.55V default and SOC will be reset/corrected to 100% on the 2.8V all loads will be stopped so that will be the 0% SOC point but SBMS0 will not make any SOC corrections at 0% SOC so if you did not set the capacity correctly the SOC indication may be 0% before the battery is actually at 2.8V or if you set the capacity higher than it actually is then it will show some higher than zero SOC value even if a cell got to 2.8V and all loads where disconnected so then you can see that value say 10% and correct your real capacity setting as SBMS0 will not do anything to SOC when battery is fully discharged (not to mention that battery will likely never be fully discharged but will almost every day be fully charged).
Yes chargers should be set around 3.55V or slightly more and they should stop when the SBMS0 say so.
Inverter can be set at 2.8V to 2.9V per cell as one cell will always be the first to fully discharge and get to 2.8V while most other cells will still be around 3V
As mentioned the charger will be set at >3.55V for bulk charge and since there will always be a cell to get there first while others will be around 3.4 it is unlikely charger will ever get in to absorption let alone float and even if by any chance it gets in to absorption current will still be higher than cell balancing current so highest cell will continue to increase in voltage and get to 3.55V terminating the charging.
Yes you can set all values to 3.6V as they will have no meaning since SBMS0 will stop the charging.
One charge to 100% per day will not do any harm to battery as that will be considered a light normal use and battery should last 10 to 20 years in normal even heavy duty operation. After that charge battery will not be charged again for 24h if you set a low SOC for recovery. Low enough that the small DC loads you may have do not discharge the battery to in 24h period.
the graph above was in Dacian's explanation and is good information to help all understand the LiFePO4 chemistry and charging. really a big thank you to Dacian for the above information.