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BQ78350-R2-DEVICE-FW: LEARN CYCLE FOR PARTIAL USAGE WINDOW

Ran Aloni
Expert 2386 points

Part Number: BQ78350-R2-DEVICE-FW

Hi all,

I have a system based on BQ78350-R2 + BQ76940 system.

I would like to optimize the learning cycle.
to choose the correct CEDV data.

the battery is a 14S14P battery - 50.4V 35Ah.

the application requires to charge the battery at 4.05V per cell = 56.7V and to discharge down to 48V (3.43V per cell).

this is basically a 80% DOC (depth of charge) and a 75% DOD (depth of discharge) = resulting a 60% window = 21Ah out of 35Ah.

what will be the best way to obtain the learning and CEDV parameters to reach optimal accuracy?

should it be done at 100% DOC and DOD ?

different way?

secondly:

battery is very large, is there anyway to go around testing at 0 deg and 45 deg? I have a physical problem to fit it in my equipment.
can I use a smaller pack for that somehow?

regards, Ran Aloni

  • 0
    TI__Guru* 81034 points

    Hi Ran,

    I recommend doing a full discharge (100% DOC and DOD) for the CEDV data collection. However, if the application will never go through a full discharge cycle, CEDV will lose accuracy over time. The Full Charge Capacity of a battery decreases with age and if the battery never discharges down to 7% SOC, the Full Charge Capacity will never be updated, so the SOC will become less and less accurate.

    The temperature testing is also pretty important for accurate gauging over your temperature range. Temperature has a strong effect on the battery discharge curve. If you can collect the data for a single cell. If you collect the data using a single cell, then you need to divide the R0 parameter by the total number of parallel cells in the pack (divide by 14). R0 is one of the 7 CEDV parameters that is returned by the GPCCEDV tool.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Expert 2386 points

    Dear Matt,

    thanks for the reply.

    CEDV:

    what will happen if I make the CEDV for 100% DOC and DOD, then change the termination parameters to fit the actual use case.

    for example the charging termination to fit 56.7V and discharge termination to 48V and design capacity to be 21Ah ?
    will this allow the FCC to update more often and improve accuracy?

    GPC:

    will it help if I do the learning cycles on a 14S1P battery and use the relative current ratios?
    that will surely fit in my equipment.

    3rd question:

    the "Design voltage" parameter in fuel gauge tab seems to be limited to 32,000mV.
    my battery is 50400mV
    what will be the impact if this parameter will not be accurate?

    thanks

  • 0 in reply to Ran Aloni
    TI__Guru* 81034 points

    Hi Ran,

    I don't have experience with the CEDV method you describe, but it may help to update FCC and improved accuracy. The one challenge is the EDV2 detection is most accurate for the steepest part of the battery curve (around 7% SOC) which gives the most accurate FCC estimation. If your EDV2 is on a flat part of the curve, FCC estimation will be less accurate.

    Design voltage should be the cell voltage in mV. The default value is 3600mV for example.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Expert 2386 points

    Hi Matt,

    what will be the highest % to have FCC learn?

    I can see that you can set it to 12%, what other parameters should I set to do it?

    Ran

  • 0 in reply to Ran Aloni
    TI__Guru* 81034 points

    Hi Ran,

    Theoretically you can set this high, but the GPCCEDV tool may limit you to 12%. The challenge is getting consistent accurate detection of EDV2 at a point on the battery discharge curve that is not steep. At 7% the curve is steep which allows for more reliable EDV2 detection.

    I do not have experience restricting the range this much. The CEDV Gas Gauging section of the TRM provides all of the details on the different parameters and describes the qualified discharge and FCC learning process. http://www.ti.com/lit/pdf/sluuc78

    Best regards,

    Matt