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Original question:

BQ27426: Question about RA update rule discharge current?

BQ27426: Questions about FCC errors after Qmax and Ra updates

Wang Dong
Intellectual 540 points
Part Number: BQ27426

hello，

Qmax：

1、One-time charging power=Qmax*37%+1mAh

2、Battery temperature is between 10-40℃.

3、Battery voltage is not in flat area

RA:

1、Discharge charge crosses a grid point

2, Discharge current = C/10

What is the error between the FCC and the true capacity of the battery when the above rules for updating Qmax and Ra are just satisfied?

  • 0
    TI__Guru 54196 points

    The error depends on many factors. It's not possible to put this into a single formula as the gauge uses a complex simulation, evaluating the behavior of the cell based on a cell model. I provided a first order analysis a few days ago via email how Qmax affects the error. Please check the email.

  • 0 in reply to Dominik Hartl11
    Intellectual 540 points

    hello Dominik,

    1、Besides the update conditions for Qmax and Ra mentioned above, what other factors will affect FCC predictions?

    2、

    Qmax：

    ①、One-time charging power=Qmax*37%+1mAh

    ②、Battery temperature is between 40℃.

    ③、Battery voltage is not in flat area

    RA:

    ①、Discharge charge crosses a grid point

    ②、Discharge current = C/10

    Assuming that all other conditions in question 1 are normal and have no impact on FCC predictions,

    What is the error between the FCC and the actual capacity of the battery when the rules for updating Qmax and Ra mentioned above are just met?

  • 0 in reply to Wang Dong
    TI__Guru 54196 points

    1: Load prediction, thermal behavior (temperature and how energy losses affect heat inside the cell), dynamic behavior (load spikes), charge termination variations.

    2:
    QMax: There's also a secondary threshold if passed charge is well below 37% of Qmax (in case this parameter is reduced to problematic levels). The secondary threshold is related to Qmax filtering and outside the scope of E2E. I discussed this with my colleague who is in direct contact with you.
    Ra: If Qmax is inaccurate or the ChemID is not a good match, the gauge may disable Ra updates.

    It's not possible to give you a numerical number for the error as this is not the result of a simple formula but a complex simulation of the cell model. This will *always* have to be simulated. And this will always be the answer to this recurring question.