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My team and I are currently trying to design a 2S2P battery pack for use in a CubeSat (student project). The pack is planned to be used with 30-40% depth of discharge for a total of around 5800 charge-discharge cycles. We have chosen to use 4x Panasonic NCR18650B Li-Ion cells. Now we need to design a protection circuit that is also capable of balancing the cells. I have found couple of chips that should do the trick, but I would like to know if this is a good design.

For balancing I have found a simple IC called BQ29209 from Texas Instruments. However it only offers balancing and additional protection circuitry would have to be implemented, such as Overcharge, Overdisharge, Overcurrent and short-circuit protection. For this I have again found an IC called S-8252 from Ablic (Previously known as Seiko), which seems like a pretty reputable manufacturer in battery protection area. Now it seems like these two IC’s together would provide full battery protection together with balancing, but my question is, can they be used together? I am imagining connecting them in way shown in the image below (excuse the crude diagram). Would that be an OK thing to do?

enter image description here

In my opinion they shouldn't interact negatively with each other as the only thing BQ29209 does is activate discharge mosfets when one of the cells goes over the voltage limit, and that shouldn’t mess with S-8252 operation, but maybe I’m not seeing something?

Thank you for your help!

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  • \$\begingroup\$ Using active balancing will better suit you requirement when energy effecientcy is critical. \$\endgroup\$
    – M lab
    Jul 23, 2020 at 20:11
  • \$\begingroup\$ Just be careful with this, Ablic protect also from discharge . TI BQ294... just overvoltage \$\endgroup\$ Oct 13, 2020 at 20:17

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I believe this would work, but you may want to consider a protection chip like https://www.ti.com/document-viewer/BQ294533/datasheet/abstract#SLUSAJ36867 as it requires less external transistors, or one with internal transistors, which may save space in a constrained application like a cubesat. Test it thoroughly, simulate various failures.

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  • \$\begingroup\$ Please don't suggest solving this privately. This is a Q&A site that strongly encourages that all answers and comments are part of the record rather than the OP and someone else getting into a private chat and solving the problem to the benefit of no one else. \$\endgroup\$ Jul 30, 2020 at 19:47

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