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BQ40Z80: Would you consider creating a new Chem ID for a LiFePO4 cell?

Masami Akazawa
Intellectual 505 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: GPCCHEM

Hello,

I apologize in advance for my poor English.

I used the GPCCHEM tool.
I attached the GPCCHEM data submitted and the report, could you please review it.

GPCCHEM1.zip

GPCCHEM1-report.zip

The report said
"Best chemical ID : 445 Best chemical ID max. deviation, % : 11.17

Summary of all IDs with max. DOD deviation below 15%

Chem ID max DOD error, % Max R deviation, ratio
445 11.17 0.48
461 12.01 0.4
6106 12.32 1.17
487 13.9 0.04
485 13.9 0.04
425 13.99 0.49
457 14.24 1.01
4124 14.34 0.53

Max. deviations for best ID is within recommended range. Chosen best chemical ID is suitable for programming the gauge."

When I used the GPCCHEM tool before, the recommended value was less than 3% DOD deviation. (The chemistry was NCM then)
So I wonder whether 11.17% is really an acceptable value.

We would like to make SOC as accurate as possible. To this end, would you consider creating a new chemical ID?

Best regards.

Masami

  • 0
    TI__Guru** 105590 points

    Hello Masami,

    Can you share your cells datasheet or specifications? (design capacity, charge voltage, etc)

    We recommend using a C/100 taper charge for LFP batteries when using GPCCHEM tool, it also looks like the voltage fluctuates very little when the load begins, so we should make sure this is a C/10 discharge rate. We should also make sure that there is 5 hours minimum relaxation after charge and discharge.

    It's common for the max DOD error to be slightly higher for LFP batteries so I don't think we will need to characterize your cell.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 505 points

    Hello Wyatt,

    Thank you for the reply.
    I'm sorry I forgot to write the information that this cell is LFP.
    And I've understood that the cell doesn't need to be characterized if its DOD deviation below 15%.

    The specifications are as follows:
    Chemistory：LiFePO4
    Nominal capacity (design capacity): 3400mAh@0.5C
    Nominal voltage: 3.2V
    Internal resistance: ≦13.5mohm(AC,1kHz,30% SOC)
    Charge cut-off voltage(charge voltage): 3.65V(end at current density of 0.05C)
    Discharge cut-off voltage: 2.5V
    Max charge current: 3.0C(10～35℃)
    Max discharge current: 3.0C(10～35℃

    Please let me know if you need any other items.

    In that cycle data, it was still connected to the charge/discharge device during the 5hours relaxation. Therefore, I think it discharged a little as the device's standby power.
    Expect for that, I think the C/10 discharge rate and 5 hours relaxation are satisfied.

    I'll try a C/100 taper charge.
    Could you tell me if you have any other remarks?

    Best regards,

    Masami

  • 0 in reply to Masami Akazawa
    TI__Guru** 105590 points

    Hello Masami,

    I think if you decrease your taper rate and eliminate the load while the battery is relaxing you will get the best chem ID match, everything else looks good according to the spec of the battery and the log.

    Sincerely,

    Wyatt Keller