• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 64 subscribers
  • Views 2350 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Cell charge balancing of Li-Ion cells in parallel

Mark Arsenault
Intellectual 420 points
Other Parts Discussed in Thread: BQ40Z50-R1, BQ24725A

We are designing a new battery pack that requires the capacity of 9 LiFePO4 cells, 3 cells in series, with 3 series strings total.  If we connect 3 cells in parallel for each of the "series cells" to form one series string, how to balance the charge in the parallel cells?  

Is our only choice to include in the pack 3 independent series strings, each with its own separate management and secondary protection IC's.  If so, how to connect the strings together for charging, discharging, protection and reading of the SMbus battery gauge of the integral battery pack?

  • 0
    TI__Expert 6575 points
    The parallel cells should balance naturally. It is recommended that the imbalance is not too large between the parallel cells, but once they are connected in parallel they will reach equilibrium without any issues. The cell balancing is more important between the series connections, so that there are no large variations in voltage between each series stack.
    The bq40z50-R1 should be able to handle your application requirement and will interface to a bq24725a as charger.
  • 0 in reply to Swaminathan Ramanathan75031
    Intellectual 420 points
    Because this application must meet ATEX Directive (protect employees from explosion risk in areas with an explosive atmosphere) requirements, we must measure to guarantee that none of the cells exceeds its charge/discharge specs. This includes parallel cells, even though we believe that should reach equilibrium naturally.
  • 0 in reply to Mark Arsenault
    TI__Genius 10785 points
    Everything possible. you can have 3 protectors if you like. It will add some cost to your system.
    But, it's a fact that parallel cells will be balanced each other quickly. You can treat as 1 cell.
    You could do quick experiment yourself to see this.