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BQ27441EVM-G1A: Questions about obtaining ChemID procedure

William Huang28
Prodigy 180 points
Part Number: BQ27441EVM-G1A
Other Parts Discussed in Thread: GPCCHEM

Hello,

We are planning to use the BQ27441 fuel gauge and we've ordered the evaluation kit to play around with it. From what I understand, I need to obtain a ChemID and input that ID into the fuel gauge. I'm looking at the following guide: www.ti.com/.../slva725.pdf and I just have a couple of questions:

  1. On step 2, it saids: "Charge using CC/CV charging to full, suing taper current, for example C/100." What is 'C'? I'm guessing that is the battery capacity (for example 2400 mAh)
  2. Is it necessary to discharge the battery completely before performing the test? Or can I start with a fully charged battery and record the relaxation period?


Thanks,

William

  • 0
    TI__Mastermind 25955 points
    Hi Willam,

    You're spot on:

    1) C stands for capacity. For example, with a 2400 mAh battery, charging at a C/100 rate would be 24 mA/h. Consequently, charging from empty at a C/100 rate, it would take ~24h to fully charge!

    2) Charging from empty, fully resting, and then performing the test gives the algorithm the best chance to update Qmax (the full battery capacity), especially for batteries with large disqualified voltage ranges. This step does not have to be done in production. For more information on Impedance Track gauges and the algorithm, please take a look at this video from a preview Deep Dive Technical Training Session: training.ti.com/impedance-track-benefits

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 180 points
    Thanks for the reply Bryan. One more question: the manufacturer of the battery suggests that standard charging to be limited to C/2 for a max. of 5 hrs. Can I use this rate in the initial charging phase during the test? Or is it still better to limit the rate to C/100 for this procedure?
  • 0 in reply to William Huang28
    TI__Guru* 76230 points
    William,
    The bq27441 is a rom based gauge, meaning you can't program a chem id on the gauge. You are limited to the only avialable hard coded chem ids which is only 3. You need to perform a test using our tool gpcchem to determine if the default chem ids on the gauge would be a match for your cells. If you do not care so much about accuracy, then you may use it if the tools says the defaults chem id don't match close enough.

    With regards to your question, you should charge the cells using c/2 rate and taper to C/100. Taper can be from C/20 to C/100, so you can choose a lower taper to save you time

    thanks
    Onyx