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BQ78350-R1: the LEDs display wrong at low temperature

Laker Lian
Intellectual 290 points
Part Number: BQ78350-R1

Hello:

         First fully charge the batteryunder and at low temperature （-30℃），the battery can discharge more than 2 hours!

Fully charge the battery ,then discharge the battery at -30℃. After a few minuters and press the LED button，only the LED1 blink .LED2...LED5  not bright.

Actually there's a lot of remaining capacity, I use five LEDs to display the capacity，So under low temperature the display of remaining capacity is inaccurate.

I want to know what am I setting up wrong?hangyu2019-1-6.gg.rar

  • 0
    TI__Guru* 81034 points
    Hi,
    When the LEDs are displaying incorrectly, are you able to read the SOC from the device? The LEDs are configured by default to reflect the SOC of the gauge. If the SOC is not accurate over temperature, the problem could be with the CEDV coefficients.

    I checked you settings file and the CEDV coefficients are still set to the default values. The CEDV coefficients are important to ensure gauging accuracy over temperature and different current loads. You need to follow the steps in Section 2.3 of this guide in order to set up the gas gauge correctly: www.ti.com/.../slua924.pdf This requires running discharge cycles at different temperatures to find the best coefficients for your battery.

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Intellectual 290 points

    Hell Sunna:

    You can see my setting files ： EDV_CMP=0，I used Fixed Voltage mode.So I think it's not important with  CEDV coefficient，

    I wonder my Fixed  EDV 2 is set too high at low temperature（-30℃）？

    My battery is 7S5P，full charged is 29.34V，When the battery is loaded with 120W，the voltage is 25.4V.

    1、Continuous load for half an hour，the voltage is 24V；

    2、Continuous load for two hours，the voltage is 23V

    All of the above are tested at low temperature（-30℃）

    Thanks!

  • 0 in reply to Laker Lian
    TI__Guru* 81034 points
    Your full charge is 29.34V. This is ~4.2V per cell.
    When battery is loaded, 25.4V. This is 3.6V per cell.
    After 30 mins, the voltage is 24V. This is 3.4V per cell. This is below your fixed EDV2 voltage. When the EDV2 voltage is reached, the SOC will set to 7%.
    After 2 hours, the voltage is 23V. This is 3.3V per cell. This is below your fixed EDV1 voltage. The SOC will set down to 3% when you pass EDV1.

    This is the challenge with using Fixed EDV values. The battery voltage curve shifts down with current load (which is why you see a voltage drop when loading the battery) and with temperature (cold temperature shifts the curve down). You will likely see much better results if you use compensated EDV. It is a little more work to set up since you need to find the right coefficients for your battery, but you will see more consistent performance over load and temperature.

    If your application operates under a constant current load and does not see much change in temperature, fixed EDV is an option. CEDV compensates the curve over load and temperature and should be used when either of these vary. Compensation will always give much better performance in general.

    Best regards,
    Matt