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BQ20Z655-R1: Fuel Gauge hack to support larger capacity batteries and higher currents

user619179
Prodigy 20 points
Part Number: BQ20Z655-R1
Other Parts Discussed in Thread: BQ40Z50-R1

Dear support,

as i understand bq20z655-r1 can perform standalone, therefore I'm considering it for our new Battery Pack project.

Unfortunately (according to datasheet page 16, "SBS Commands" table) maximum current is 32A, and capacity 65Ah.

I need more than 300Ah capacity and 300A discharge current.

In datasheet (page 20) application schematic, 10mOhm shunt rezistor is used.

Let say i change shunt resistor to 1mOhm and make the bq20z655-r1 think that 1A current flows (while actual current is 10A), capacity should go up 10 times.

The question is: will State of charge calculation algorythm perform properly if bq20z655-r1 sees 10 times lower current than actually is.

  • 0
    TI__Expert 6575 points
    Hi,
    Your idea of using scaling is correct to tackle high capacity, high discharge rate applications. However the input range to the Coulomb counter is only +-200mV, so with a 1mOhm sense resistor and 300Amps discharge current you would get 300mV, which will exceed the input specifications.
    Also, the recommended sense resistor value for bq20z655 is 10mOhms, and the accuracy will really drop if a 1mOhm sense resistor is used.
    The alternative might also be a bit of a stretch, but I think a bq40z50-R1 could be used with a 0.2mOhm sense resistor, and a similar scaling technique could be used to accommodate the 300Ah capacity and 300Amp discharge rate. (The recommended sense resistor value for bq40z50-R1 is 1mOhm, and the voltage input range for the coulomb counter is +-100mV)
    Please let me know fi you have any questions or comments.
    Regards,
    Swami