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Original question:

BQ27Z558: Acquiring Chemical ID and Completing Learning Cycle - Actual Using Range or Cell's voltage range

BQ27Z558: BQ27Z558

sunghyun jo
Prodigy 40 points
Part Number:

Tool/software:

Hi
we have a problem with battery learning.
After fully charging the battery and disconnecting the charging cable, the SOC drops right down to 100% -> 99%

When we did battery learning before, the battery pack is 4450mA but we are using it with 4380mA, how should we do the learning?

In reply, I was told that I should learn with 4450mA, but I get the same problem as above.

I was told that training with 4380mA will solve it.
I am asking again if I should train with 4450mA or 4380mA.

Or is this problem caused by something else?

Translated with DeepL.com (free version)

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BQ27Z558: Acquiring Chemical ID and Completing Learning Cycle - Actual Using Range or Cell's voltage range

Tool/software:

Cell : 2.5V ~ 4.45V

Actual Using Range : 3.4V ~ 4.38V

For acquiring data for chemical ID and complete learning cycle, should I conduct test with only cell's voltage range?

If it is okay to conduct it under actual using range, I would like to do it with actual using range.

I would appreciate it if you review them and let us know.

Thanks for your supporting.

Thanks.

Jaiyong Park

->

Hello Jaiyong, 

You base your learning cycle on the cell range and not on the actual using range, I've attached the GPCCHEM calculator that gives you your actual chemID.

GPCCHEM:
https://www.ti.com/tool/GPCCHEM

Thank you,
Alan

  • 0
    TI__Guru 61006 points

    There are several parts to learning:

    1. Qmax
    2. Ra
    3. Charge Termination
    4. Typical Load

    1 and 2 are not related to how much capacity you want to get out of the cell. So if you use a cell with a nominal capacity of 4450mAh but you only want to use 4380mAh, then you can run the learning cycle for 1 and 2 with a cycle that charges and discharges 4450mAh (or close to this). In fact, you'll have to because the gauge requires a DOD change >0.9 for a dedicated learning cycle (UpdateStatus = 0x08).

    3 depends on your charging setup. If you want to only use 4380mAh and you do this by limiting charging (e.g. lower charging voltage and higher taper current) then you have to configure the gauge for this new setup or you need to let it learn the charge termination. See TRM, 9.8.

    The gauge will learn Cell 1 Chg Voltage at EoC and Current at EoC (as describedin 9.8). You can set these two values manually if you want to but you also must make sure that the ChargingVoltage() is correct for your 4380mAh use case so that the gauge can reliably detect a full charge (which is a requirement for the gauge to reliably calculate SOC = 100%).