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Original question:

BQ78350-R1: CEDV config

BQ78350-R1: Some questions about CEDV algorithm and configuration of the CEDV coefficients on BQ78350-R1

Alexey Trubachev
Intellectual 520 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, BQSTUDIO, BQ34Z100

Hello.I would like to thank the TI staff for their help in resolving the issues, and want to ask a few questions to clarify the operation of the CEDV algorithm and the configuration of the BQ78350.

1.To calculate the CEDV coefficients, in addition to the room, it is necessary to test the battery at high and low temperatures. For example, take the temperatures recommended by the GPS Packager application in bqStudio program - 0 degree C, 25 degree C, 40 degree C. To better calculate the coefficients, it is necessary to maintain a stable ambient temperature - for example, using a thermal camera, or you need to strive to maintain a stable temperature of the battery and cells, for example, use a battery with a fan? In the description of the algorithm says, that the algorithm analyzes the self-heating of cells, but if I test the battery with a current of 1C at 40 degrees, it can heat up to 50-60 degrees during the discharge process. Would it be normal to calculate the CEDV coefficients? Do I need to cool the battery in this situation?

2.The batteries need to be tested at the average normal current, and average maximum current. For example I use the battery with capacity 50Ah, for electric car. The nominal average current consumption will be 25-30A, the maximum average current 50-60A.But at the time of start or when fully loaded, peak nondurable currents can reach 100-120 A. I'm running tests for the CEDV battery ratios at 25A, and 50A..Should I conduct a 50A current test continuously, or can I give an additional short-term load of 100-120A during the test, to better match the actual operation of my application? 

Please tell us in more detail.

  • 0
    TI__Guru* 81034 points
    Hi Alexey,

    It is necessary to test the battery over temperature if you need the gauge to be accurate over temperature. Temperature does have a very big effect on the battery characteristics, so the CEDV coefficients will compensate for this. To collect this data, try to set a stable temperature in your testing chamber and attach thermistors to the surface of the cell. It is normal for the battery temperature to rise with high current, but the CEDV tool will take this into account.

    For the load current, you should use a constant current (50-60A in your case).

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Intellectual 520 points

    Hello Matt, thanks for the reply. I found this document, it says that (page 2) "Discharge does not have to be constant current. It can be any load pattern typical for your application, including constant power."  Is this information outdated? Is it possible to calculate the coefficients yourself using the formulas contained in this document? And is it necessary to conduct a separate test for BQ78350 to determine the type of cell chemistry, as in the case of chemistry bq34z100??Simple guide to CEDV parameters calculation in MathCad.ppt

  • 0 in reply to Alexey Trubachev
    TI__Guru* 81034 points
    Hi Alexey,

    I'm sorry, you are correct. The discharge current can vary. There is one condition to be aware of though: It is very important the discharge is continuous, e.g once at least one discharge point with negative current is present (discharge has started), there should not be any zero current points until discharge finishes, since tool would interpret any zero point as end of discharge.

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Intellectual 520 points
    Hi Matt. That's great news. so I can take my battery, and as the average maximum current to use 50-60 amps, periodically for a short period of time increasing the current to 100-120 amps to simulate the actual operation of my device, under the main condition that I will use an electronic load, and the current will go continuously?

    Should the values and time intervals of the test currents be the same at different temperatures? I think it would be right. If at 0 degrees I will, as an example, use the following mode:

    1) 100A for 5 seconds
    2) 50А for 10 minutes
    3) 100A for 10 second
    4) 60А for 20 minutes
    5) go to 1 (until the battery reaches terminate voltages (2100mv per cell in my case).)

    That for a temperature of 20 degrees I should use the same cycle for greater reliability of results?
  • 0 in reply to Alexey Trubachev
    TI__Guru* 81034 points
    Hi Alexey,

    Yes, you plan is correct and using the same cycle at different temperatures is the right approach.

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Intellectual 520 points
    Thank you very much for your help Matt, I will experiment.