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BQ27531-G1: BQ27531-G1 DATA COMMANDS

Part Number: BQ27531-G1

Hello,

We are using BQ27531-G1 on a PCB that is used to analyse the batteries. After charging and discharging, the test result is shaped by the voltage interval of the batteries. If they are in a range which is determined by us, they pass.

Sometimes the batteries fail on the real device in different aspects and in order to eliminate these already failed batteries before using on the device, we want to increase the capability of our PCB by enhancing our data variety that can be taken from the Gauge IC. 

In this regard, what parameters could you suggest us to take from the BQ27531-G1 to eliminate the batteries that are operate unnormal? I think because it is an analog measurement, voltage values are more reliable than the SoC values. Therefore, we are using a voltage measurement range as a test parameter. 

Can we get "internal resistance" (DC) of the batteries (I couldn't find something like that on the datasheet), or something that could help us sort out? Thanks in advance.

Best Regards,

Caner

  • Hi Caner,

    This entirely depends on what your criteria is for qualifying a good/bad battery. Can you provide me with more detail on how you are running your tests and what criteria you are looking for? Strictly using voltage values can be very unreliable as the voltage of the battery can vary across temperature and load on the cell. Especially within the flat region of a batteries OCV curve, even a small voltage drop can cause the state of charge to drop > 20% simply from applying a load if you are just looking at voltage.

    If you are trying to see the max voltage range of a given cell to see when it terminates charge, this may be a more viable option but I think more details on your test setup and intended application would help greatly here.

    Best,

    Jackson

  • Hello Jackson,

    Thank you for your quick reply.

    We do test operation by putting the batteries on a battery test jig and the jig charges the batteries up to they are fully charged. Then, discharging starts... (for 2880mAh batteries, 750mA current is used to drain from them during the discharge) this discharging operation takes 720 seconds. According to the result after discharge, if the voltage values of the batteries are in a range that we desire, they can pass. We were using SoC result with a range of 90% - 99%. 

    These batteries, even if they pass the test, may come back to us from the devices (not the jigs) because they cause a problem related to them. What kind of precautions can we also take to eliminate these failed batteries before they reach to the products by improving the capability of the jig via gauge IC? 

    Thanks in advance Jackson.

    Best Regards,

    Caner

  • Hi Caner,

    Using voltage values to characterize the batteries in this way can be very inconclusive. This is because 1. After charging (especially at a rate of 750mA), the cells need time to let their voltage settle. This can take anywhere from 2 - 5 hours if you want an accurate voltage reading. On our gauges, we only use these voltage correlations when the cell has satisfied the condition of < 4uV/s. Also, the internal impedance of the cell (this can vary over temperature) can affect this voltage value.

    A much better alternative for this type of test would be to look at the RemainingCapacity() parameter. The value here reflects a much more accurate picture of how much capacity has actually been drained from the cell. It is reported in mAh and is derived by our Impedance Track gauging algorithm that is vastly more accurate than a simple voltage reading. For this to be accurate it is also important that the gauge has the correct ChemID programmed in so that it correlate all of these values to an accurate SOC for that given cell.

    Best Regards,

    Jackson

  • Hello Jackson,

    You helped a lot! I am so appreciated. Thanks.

    Best Regards,

    Caner