BQ20Z655: Remaining capacity calculation

Franz Schellhase

Part Number: BQ20Z655

Hi team,

Can you have a look at the following customer question please?

I can display the capacity values either in mAh or mWh by the CapM bit. I have set the bit and the values for e.g. the Remainig Capacity are now displayed in mWh. Originally my battery displayed 4312mAh, after setting the CapM bit it now displays 59780mWh. If I calculate the voltage from both values I get 13,863V. Where does the BQ get this voltage when it converts the values ? Which voltage is used for the individual capacity values e.g. Full charge Capacitiy etc.? ?

Thank you,

Franz

over 4 years ago

0 Wyatt Keller over 4 years ago

TI__Guru** 105760 points

Hello Franz,

The voltage should be the stack voltage of the pack.

Sincerely,

Wyatt Keller

0 Marcus Mueller2 over 4 years ago

Prodigy 80 points

Hello, at the moment of switching from 4312mAh to 59780mWh the stack voltage was 16,043V and not 13,863V as calculated (59780mWh/4312mAh=13,863V)

0 Wyatt Keller over 4 years ago in reply to Marcus Mueller2

TI__Guru** 105760 points

Hello Marcus,

The gauge does not use the straight stack voltage to calculate Wh, this would not give the correct value because voltage decreases during discharge. The voltage you found is what the gauge calculated to be essentially the nominal voltage during discharge according to it's learned parameters.

Sincerely,

Wyatt Keller

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BQ20Z655: Remaining capacity calculation