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BQ40Z80: Networking to parallel connected battery packs... Possible?

Part Number: BQ40Z80

Hi,

We are considering using the BQ40Z80 for an application with a 6S, approx 4AH li-po battery pack.

I'm currently using the BQ40Z80EVM-020, and the device appears to cater to our requirements for balancing, monitoring, protection, and gauging.

However, one additional requirement we have, is to allow for multiple battery packs to added to the Device being powered, to extend run time.  The packs would be wired in parallel to maintain the same voltage with extended AH capacity.  The number of packs added to the one device, will depend on how long the user wants to extend run time.

If each battery pack includes it's own BQ40Z80-based BMS, is it possible to configure the pack to talk to other BQ40Z800 based packs connected to the same SMBus?

The purpose of this networking would be:

  • To have the ability to press a button on any one of the battery packs to activate the output of that pack (enable the DSG FET), as well as any other pack connected to the same SMBus (without having to turn on each pack individually)
  • Communicate the status of each pack to the device (remaining charge, cell voltages, etc)
  • Allow any one of the packs to shut down it's output in the event of a protection function being tripped, while allowing the other packs fitted to the device to continue powering the device

I have attached a diagram to illustrate the basic architecture.

Thank you,
regards,
Daniel

Battery Pack configuration (1) (1).pdf

  • Hello Daniel,

    It doesn't seem that it is recommended to use the BQ40Z80 in a parallel configuration.

    See the following thread for more information: https://e2e.ti.com/support/power-management/f/196/t/812279

    Have you considered using the BQ40Z80 in a 6s4p configuration? It would give you most of the features you want.

    Besides the issues detailed in the thread above, I don't believe it's possible to network these devices through a single communication line to the MCU. SMBus is based on I2C communication, and all of the BQ40Z80 gauges would have the same non-programmable address, which means that you might not able to communicate as the devices share the same address. You might have to add external circuitry to make it work.

    Best Regards,

    Luis Hernandez Salomon

  • Thank you Luis.

    We cannot use a 6S4P solution, as we might not always want all 4 packs fitted.  If only a short run time is required by the user, we may have only 2 or 3 packs fitted.

    I'm considering adding a microcontroller and CAN or RS485 transceiver to the pack now, to manage the pack networking and control each of the BQ40Z80's in each pack.

    I neglected to mention another question I have about the BQ40Z80:  Does it support an automated "Self-discharge to storage" function?

    That is, the BMS might initiate a self-discharge of the pack to a safe storage voltage (to increase the lifespan of of the li-ion cells) after a set period of inactivity (eg. after 2 weeks or so, the pack begins to discharge itself until it reaches 30-50%)

    If the BQ40Z80 cannot support this - do any of your BMS IC's support such a feature?

    thank you,

    Regards,
    Daniel

  • As far as I know, I don't see that we have such a gauge device that supports the "self-discharge to storage" feature.
     
    Andy