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BQ24610: Charging Multiple Li-Ion Battery Packs in Parallel (4S18P)

James Hinshaw
Prodigy 40 points
Part Number: BQ24610

Hello,

I was planning on using the BQ24610 to charge a 4S18P Li-Ion battery pack. The maximum listed charging current for this IC module is 10A, so the charging current per series connection for my application would be approximately 10/18 A (0.56 A). Using the specifications and design guide from the data sheet, I was able to conclude that I could achieve a 10A (0.56 A per cell) charge current and 5.4A  termination current (0.3A) per cell by adjusting the sense resistor RSR to 3.7 milliohms and matching the impedances of the traces back to the sense pins with appropriate VISET1 and VISET2 values. My question then becomes: Are there any pitfalls (not safety related) for an approach to charge a 4S18P Li-Ion battery with only one battery charger? Moreover, will issues arise when using only 0.56A to charge a cell with a cutoff current at 0.3A, maybe due to a combination of noise and resolution in the sense comparator for the system? One alternative I considered was to use multiple chargers (assuming sufficient input power) with relays to disconnect the battery packs; however, I dislike this approach because I estimate a power loss of around 10 to 20 watts during discharge because of the efficiency of a relay. Ergo, if I cannot use one charge to charge 18 of these battery packs in parallel, what is the limiting factor for the maximum amount of battery packs that I can charge in parallel for this particular integrated circuit?

Thank you in advanced for your time and patience

  • +1
    TI__Mastermind 40305 points

    Hello,

    A big problem is that the current to each battery in parallel will probably not be evenly distributed. The charger is only monitoring the total current not each individual current. Therefore, termination can be an issue as some might terminate at higher current and some might terminate at lower current.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0
    Prodigy 40 points

    Hi,

    First, thank you for your input. Can you please elaborate on what you mean by "big problem?" Will this problem lead to 90%, 50%, 10% expected battery life? Will this problem reduce the overall energy capacity by 90%, 50%, or 10%? If the batteries are carefully matched beforehand so that current is distributed fairly evenly then can this problem be avoided? Alternatively, can a battery balancer IC be used after the charger terminates to balance the battery, then attempt to finish charging after the batteries are balanced? 

    Thank you again for your time and patience

  • +1 in reply to James Hinshaw
    TI__Guru** 105590 points

    Hello James,

    If your cells are all from the same lot they should have similar internal impedance, as long as you balance the series cells during cycling and the interconnection resistance between all the cells are low it should be fine.

    As Michael mentioned if the cells become unbalanced, one of the series strings could cause the whole pack to terminate early since the charger only sees the total current, leading to the cells becoming more and more imbalanced over time. 

    Sincerely,

    Wyatt Keller