PylonHV

That may not be true, as the voltage of new modules is around 50VDC

Pylontech High Voltage Battery UnBalancing Problem
 
Greetings! A new forum member here,
Respected forum members Youda and other worthy members who have the experience of using Pylontech High Voltage Battery system may kindly provide the possible solutions to the following Problem.
System Information:
We have a Residential 10kW Hybrid Inverter attached to Pylontech High Voltage Battery Pack with a total capacity of 14.4kWh.
BMS is Pylontech SC0500-40 (37Amps), it communicates with the inverter via CAN BUS protocol,
Battery Modules are Pylontech H48050, 2.4kWh (50Amps) each,
6 Battery modules are connected to the BMS (initially 4 modules, with addition of 2 more modules).
Problem:
·        To keep it simple we will take the example of 3 Batt. modules connected to the BMS.
·        Initially when batteries are charged, 2 batt. modules have Balanced Cell Voltages i-e difference of 20milli Volts between the cells and this is maintained all the way to 100% charging.
·        3rd batt. module has UnBalanced cells with Voltage Delta of more than >100milliVolts(0.150Volts) between minimum and maximum cell voltage.
·        The BMS first charges all the modules to 100% State of Charge (SOC) and then balances the cell voltages to around 3.4Và3.3Volts with SOC at 100%.
·        During Discharge cycle when the SOC reaches 45% the Batt. module which was initially having UnBalanced cell voltages (but later it was balanced by BMS) just drops the SOC from 45% à35% à20% which is the Cut off for the BMS. At this stage its cells voltage also become UnBalanced Again.
·        While the remaining 2 Batt.modules which had initially balanced cell voltages remain at 45% SOC.
Queries:
1.      If the BMS balances all the 45 cells in 3 batt. modules at a specific voltage repeatedly, then why one module drops State of Charge (the one with the initial ImBalanced Cells)?
and it does Not seem to be a problem with one particular module, by hit and trial the UnBalanced module can become balanced and Another module may start to have Unbalanced Cell Voltages.
2.      The basic issue seems to be cell UnBalancing.
 
3.      During every charging cycle, the cells of one of the Batt module become UnBalanced, but the Pylontech BMS  Balances the cells on daily basis after SOC reaches 100% , however at the next discharge/charging cycle the cells are UnBalanced again? And again the BMS balances all. Why is this so? This has continued for 2 months now.
 
4.      During Discharge cycle, why the cells become UnBalanced below 45% (SOC) and the battery charge rate drops suddenly if the BMS has balanced the cell during charging cycle?
 
The overall effect is that the Backup Time of the Battery is Cut by Half.
 
Solution to the above problem will be highly appreciated.
 
Have attached a few pictures from Battery View Software here: