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BQ40Z50: Modular battery packs: realistic solution?

Michel C
Prodigy 155 points
Part Number: BQ40Z50

Hello,

I want to buld a modular battery pack composed of two distinct boxes (see drawing below):
-Base Battery Pack: 2S2P battery pack with BMS. The 3-pins connector enable extension to add more battery cells.
-Extension Battery pack: it is 2S3P without BMS

The Base battery pack can be used alone. The Extension battery pack is never used alone.
If more power is needed, the extension battery pack is connected (through the connection cable) to the base battery pack.
The Extension battery pack is charged through the Base Battery pack.

Is this solution feasable? drawbacks: safety, efficiency, problem with extra length of the connection cable....?

Thank you for your help,

Michel

  • 0
    TI__Mastermind 42535 points
    Hi Michel,

    In theory this is a great idea. But however the way the fw works, this application will not be supported. If you just connect the base pack and do gauging you will get the resistance of the cells measured as 2s2p. Hence your design capacity, qmax and other gauging parameters will be set for a 2s2p config. When you attach the external pack, it suddenly becomes a 2s5p config. With this config, your capacity increases, cell resistances decrease and because of this the control values that we use in the gauge are thrown off. Unfortunately, because in IT we monitor the values for aging etc we can't accommodate such drastic changes. Therefore it will not be accurate and won't work.

    But, from an engineering point of view this is definitely a good idea. Unfortunately the bq40z50 doesn't support it.
  • 0 in reply to Batt
    Prodigy 155 points
    Hello Batt,

    Thank you very much for your clear response. It is an honor to be encouraged by a Genius level of the TI forum :-)

    So it is a matter of battery pack config management inside the fw...Ok, I will try my luck anyway:
    Is there any chance to get special fw that manages multiples 2SxP configs dynamically?
    For example, a third pin of the connector is used to detect the (dis)connection of the Extension battery pack and then switch to the 2S5P (or back to the 2S2P) config?


    Regards,
    Michel
  • 0 in reply to Michel C
    TI__Mastermind 42535 points
    Michel,

    Thanks for your kind words. Unfortunately, there is no way to dynamically change capacity that way in the gauge. Either way, what you propose requires both a hw and a fw fix. Both these things aren't easily done. Sorry about it.