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Dual battery management

Yoav Benita
Intellectual 285 points
Other Parts Discussed in Thread: BQ40Z50

Hello everyone,

I need help designing a circuit / finding a component, which can perform management of two batteries that are connected in parallel. Two separate components can be use if they know how to work together but it is better not to.
Mandatory requirements:
1. The two batteries are with the following data: 4S1P 14.4V 3.45Ah 49.7Wh Li-Ion
2. Voltage range 10-17V, maximum 5A.
3. No need to charge the batteries (if there is and it is possible not to activate the function - possible).
4. Serial use of batteries. That is, discharging the first battery up to a certain threshold voltage (preferably for a component that can be programmed to this voltage threshold), then transferring the discharge to the next battery. Meantime replacing the first battery, and goes on. Switching time between replacing battery usage is as low as possible.
5. Smart battery support (the battery communicates on SMBus).
Pros:
1. Reverse voltage protection.
Thank you

  • 0
    TI__Guru 57697 points

    Hello Yoav,

    You can use bq40z50. This goes in the the battery pack and each pack will have its own independent gauge. You may want to add circuitry(diodes) to prevent one battery from trying to charge the other since this may cause large current and trigger protection functions. The microcontroller will need to communicate with each battery independently. There are FET control commands that can be used to select which battery to use for discharge. But it is probably unnecessary since current will flow from the battery that is charged. The old battery can be removed at this time.

  • 0 in reply to Shirish
    Intellectual 285 points

    Hi,

    I probably did not explain myself well.
    My two batteries are connected in parallel, but their use will be done in serial form.
    That is, use one battery until it "runs out", then move on to using the other battery (again, for as short a time as possible)
    Thanks

  • 0 in reply to Yoav Benita
    TI__Guru 57697 points

    Hello Yoav,

    Can you draw and post the proposed connections? That will make it easier to understand. Thanks.

  • 0 in reply to Shirish
    Intellectual 285 points

    Hi,

    I made some changes in my architecture:

    The voltage flow is:

    BATT1 is discharge into the system until it reaches 10V. In this case, the power manager switch the V_SYS to BATT2. In that time, the user knows that he needs to replace BATT1. After doing so, the power manager switch the V_SYS back to BATT1. I tried to draw it, hope it is clear enough:

  • 0 in reply to Yoav Benita
    TI__Guru 57697 points

    Thanks Yoav,

    The power section will work fine.

    Some concerns on communication. Both the batteries will have the same SMB address, so there will be communication issues when both batteries are connected. I would recommend that the power manager also switch the SMB lines. You can use a I2C/SMBus switch. If the FPGA has 2 separate SMB ports, then you can switch it from the FPGA

  • 0 in reply to Shirish
    Intellectual 285 points

    Hi,

    Is the bq40z50 a good solution? If not, can you recommend me another component please?
    Thanks

  • 0 in reply to Yoav Benita
    TI__Guru 57697 points

    Hello Yoav,

    The bq40z50 seems to be best solution. Any system with dual batteries will need to accommodate communication with 2 separate batteries. The "concern" was with both batteries being on the same SMB communication lines. I think i could have phrased the previous answer better. I see two separate SMB lines to the FPGA. In that case the concern does not apply to your case.

    The bq40z50 also has a feature where you can change the device SMB address to have 2 batteries at the same time on the same bus. I did not suggest that as your use case seems more like a single battery with swap capability without system shutdown. You can check if that feature may be useful in your case.