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Stackable Multicell balancer for series/parallel cells

Darren DeBattista1
Intellectual 525 points
Other Parts Discussed in Thread: BQ76PL455A

Hi,

We have a new industrial/consumer project were we need to design a BMS for a multicell battery pack which can be configured either as 4S2P or 8S1P. The configuration should be switchable during operation (ie, the micro in the BMS would switch the cells as needed). I am looking for a cell balancing chip which could be used in such a project. My thought is to use a two stackable battery balancers and make two battery packs with a 4S1P configuration. I would than either cascade the battery packs to create the 4S2P or connect them in parallel to achieve the 4S1P configuration.

I am still relatively new to battery management so any help would be very appreciated. Is my idea the proper way to go or are there issues with my idea I'm not considering? Could you suggest any ICs and evaluation boards which could be used to achieve this task?

Battery Pack Specs:  Li-Ion 14V @ 20A (4S2P) and 28V @ 10A (8S1P)

Thanks

  • 0
    TI__Genius 17370 points
    Hi Darren,

    Thanks for the interest and welcome to the TI - E2E forums. The best place to start would be to review the datasheets and associated technical documentation for the bq76pl455a and bq79606. I think the bq79606 (www.ti.com/.../technicaldocuments) fits this project better as one device can monitor/balance up to 6 cells and it is stackable up to 51 devices. Also there is integrated cell balancing FETs that can balance up to 150mA. As for the parallel cells, you can use the same bq79606 to monitor cells in parallel because the voltage does not fluctuate across parallel cells but ultimately it is up to the customer to decide whats best for their needs. Here is the link to our evaluation module: www.ti.com/.../bq79606evm-897

    Best Regards,

    Taylor
  • 0 in reply to Taylor Vogt
    Intellectual 525 points

    Hi Taylor,

    Thanks you for your reply. I gave a look at both device's datasheet. One question I have in mind is regarding the parallel connection. When stacking two devices on the same PCB using a Daisy Chain connection, capacitive coupling is used. Taking the bq79606 for example, the COML and  FAULTL of one device are connected to the COMH and FAULTH of the second device were the 'H' suffix denotes the device at a lower potential (bq79606 datasheet, first figure). 

    In the case of a parallel connection of the devices, how would this Daisy Chain be connected. Would it still need capacitive coupling? Are there other consideration to take care of when connecting these devices in parallel?

    Thanks

  • 0 in reply to Darren DeBattista1
    TI__Genius 17370 points
    Hi Darren,

    It depends on whether you are talking about parallel cells or parallel devices (bq79606s). For parallel bq79606s, we offer an alternative to daisy chain connections called multi-drop which is explained in section 10.3 of the datasheet. For parallel cells, the daisy chain is indifferent and it is just your connections on the VC/CB/BAT pins to the cells that matter.

    Regards,
    Taylor
  • 0 in reply to Taylor Vogt
    Intellectual 525 points

    Hi Taylor,

    Sorry for my late reply. I checked regarding the multi-drop connection and I saw that it connects the communication in parallel but keeps the cells in series. My need is to set the series/parallel connection as shown in the attached image. Is something like this possible with the bq79606?

  • 0 in reply to Darren DeBattista1
    TI__Genius 10785 points
    Hi Darren,

    606 can support both configurations.
    Just like Taylor said, you need to know yourcell configurations.
    If you have 5S2P then you only need 1 606.
    Yes, you can monitor each cell as you shown on your images.

    Roger
  • 0 in reply to Darren DeBattista1
    TI__Genius 10785 points
    Hi Darren,

    I will close the thread.
    thanks

    Roger