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Feul Gauge and Protections for Multiple 18650 Cells in parallel connections

user4687076
Prodigy 120 points
Other Parts Discussed in Thread: BQ27542-G1, BQ24195

I plan to use multiple Li-ion cells (18650, mostly I need 4 cells) in parallel connections for portable devices, and about to realize the following functions:

2A/4A Charging (with protections), precise percentage (1% or so) of the total electrical volume, I have chosen BQ29700(Protection),BQ24195(Charge IC), BQ27542-g1

So I have some questions:

1.Can I use one gas gauge for multiple cells in parallel connection? What should I concern, other than single cell uses?

2.Some of the 18650 cells already have protection board built in, (usually DW01+ 8205A, which is more expensive than cells only), do you suggest I use the built in ones or BQ29700? Or, do you suggest I use both if I need protections of each cells?

  • 0
    TI__Mastermind 26705 points
    1. You can use one gas gauge for multiple cells in parallel. You will want to adjust your design capacity appropriately (design capacity of 1 cell x number of cells in parallel).

    2. For 1S4P, I would just use a single cell protector. Whatever bq297xx you choose, make sure the overcurrent levels is set appropriately for your system.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 120 points

    Benjamin Lough said:
    1. You can use one gas gauge for multiple cells in parallel. You will want to adjust your design capacity appropriately (design capacity of 1 cell x number of cells in parallel).

    2. For 1S4P, I would just use a single cell protector. Whatever bq297xx you choose, make sure the overcurrent levels is set appropriately for your system.

    Best Regards,
    Ben Lough

    Hi Ben, thanks for you reply.

    So you suggest us to use one protector and one fuel gauge (e.g., BQ29700 and BQ27542-g1  for our case) to take care of multiple cells. I am not quite familiar with the chemical principle of Li-ion batteries, what I worried is if different cells have slightly different charge-discharge characteristics, which leads inaccuracy after a few cycles.

    Kenn

  • 0 in reply to user4687076
    Prodigy 120 points
    Another worry is using one protector, if one of the 4p cells damages and shorts, how can this single protector work?
  • 0 in reply to user4687076
    TI__Mastermind 26705 points
    1. Typically you use multiples of the same battery in parallel. It is uncommon to place two batteries with different discharge profiles in a parallel configuration.

    2. Most protectors work at a pack level. It would not protect against an individual cell short.

    Best Regards,
    Ben Lough