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estimate runtime availible in lithium ion battery

Keren Davidpur
Prodigy 20 points
Other Parts Discussed in Thread: BQ27210, BQ27010

Hello

I am trying to estimate the remaining time of a lithium ion battery before it empties. It is connected to a DS2781 fuel gauge, which can estimate remaining active (and stand-by) absolute capacity...can anyone tell me how to extract the remaining runtime of the battery? 

any help would be appreciated...

thank you very much

Keren

  • 0
    TI__Genius 14985 points

    Hi Keren,

    That is not a TI fuel gauge that you are talking to and I don't believe it has the feature to estimate remaining run time that is found on many TI fuel gauges.  For example, the bq27210/bq27010 fuel gauge has several registers to estimate time-to-empty (TTE).  Also, the more modern bq275xx fuel gauges with Impedance Track would be even more accurate at this estimation.

    A crude way to estimate run time based on the remaining capacity would be to divide the capacity (mAh) by the system load (mA) to estimate hours remaining.  However, most systems use constant power (mW) loads as they typically use switching voltage converters.  This means that the current consumption will increase as the battery voltage decreases in order to maintain a constant voltage output.  The end result is that if you are estimating run time based on a constant current, you will over-estimate the run-time.

    The TI fuel gauges using the Impedance Track algorithm will be the most accurate in this case since it can be configured to estimate capacity and run-time based on either constant current or constant power loads.  This is what the Load Mode setting is for.

  • 0 in reply to dMax
    Prodigy 20 points

    thank you very much for your answer :) i will start reading about the impedance track algorithm

    by the way, I was referring to this fuel gauge:

    file:///C:/Users/owner/Downloads/datasheets.maximintegrated.com_en_ds_DS2781.pdf