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Calibration: fast discharge via a resistor?

Noah Harris
Intellectual 410 points
Other Parts Discussed in Thread: BQ27200

Hi,

When using a battery gauge like bq27200 the user is usually expected to do regular calibration periodically by first discharging the battery to empty and then charge to full, in which course the gauge learns the latest capacity.

If we want the discharge to be performed quickly in order to save time, what is the best way to do that? First, I guess one could ran the full device at full clock rate to increase its current consumption, but doing this might have adverse effects in the long term; another way is to use a power resistor + transistor combination in which the transistor acts as the switch, and when fast discharging is needed the software simply opens the transistor’s path to let the majority of the current goes through the power resistor so that capacity is dissipated as heat and does not require the device to run at fast speed.

Is there any recommended practice?

 

Noah

  • 0
    TI__Genius 14985 points

    Hi Noah,

    There isn't any recommended method to accomplish the learning of LMD in the bqJunior gauges.  Usually we expect it will periodically get discharged to 6.25% during normal operation.  It doesn't need to do this very often, but there is an option to have it automatically de-rate capacity if the learning discharge doesn't occur.  It will probably err on the conservative side.  Your idea to use an external load is completely valid, but don't make the current too high.  For one, you can wear out the battery faster with higher current (and high heat). Keep the current within the range of loads you used when determining your EDV1 coefficients.  If you plan to initiate a learning discharge, confirm the VDQ bit is cleared after full charge before you start your discharge.  Then make sure it stays cleared all the way down until LMD is updated.

  • 0 in reply to dMax
    Intellectual 410 points

    dMax,

    Thanks for your answer. We will use software to control the discharging instead of using an external resistor or alike to dissipate energy.

    Noah