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Original question:

BQ27520-G4: question about SOH update

BQ27520-G4: question about SOH update

TS Yang
Genius 4800 points
Part Number: BQ27520-G4

Dear TI,

This has helped me to understand the Qmax update of the BQ27520.

Based on this information, I am looking for the SOH information of a specific battery,
I have a few issues and would like to contact you again.

1. The SOH value is not correct.

I measured the SOH of a somewhat obsolete battery (92% available) and it was still displayed as 100%.
(The basis of 92% is the result of discharging a fully charged battery of 4.35V at 0.2C and based on the actual discharge time.)
This battery is derived from the traditional Qmax update method, but the SOH is displayed as 100%.
In this case, even if we use the Fast Qmax update function, it is displayed as 100%
which part is wrong?
- Full charging / Relaxation 2 hours -> Full discharging / Relaxation When DOD is determined after 5 hours
The SOH value is displayed as 100%. (This is the Traditional Qmax Update.)
- The SOH status value was 0x3 when displayed as 100%. (SOH value ready)

2. If we use only about 80% of the battery, whether Qmax is updated or not.

This is a Q4 related inquiry.
Currently, the battery can be charged up to 4.35V, but in some cases it is only charged to 4.2V.
However, the charge / discharge related parameter of BQ27520 is 4.35V.
- Based on 4.35V Designed capacity: 2950mAh, Charging termination current: 150mA
- Based on 4.2V Designed capacity: 2360mAh, Charging termination current: 250mA or 4.35V

Even in the Qmax update condition of Traditional or Fast method, FC bit ON seems to be a prerequisite in charge state in DOD point determination. However, in the above situation, the FC bit will not turn ON.
Is the Qmax update possible under this condition?

As more and more customers are demanding smart batteries, smart battery related functions such as battery life cycle and cycle count are becoming important factors.
If our laboratory has a technical understanding of this area, I think it will be the foundation of business.

Sorry for the trouble, but I'll wait for your meaningful answer.

thanks,

TS

  • 0
    TI__Guru* 76230 points
    hi TS
    -For the gauge to correctly report SOH, it has to learn the qmax and the resistance of that degraded cell. if you are using the golden file to learn chances that only one cycle would be sufficient is slim because the qmax and ra filters which has been activated by update status 02 will limit how much qmax and resistance can change during just one cycle. So you might want to run several cycles until the qmax reports a value close to the 92% you said the bad cell has other wise simply set back update status to 00 and Ra flags to their default to allow learning during just one cycle to occur for that bad cell.
    - if you are using just a certain percentage of the capacity of your cell in your application, i.e not using 100% capacity, you can set the design capacity 'to reflect that only after you have done the first original learning cycle with the actual capacity and fully charging and discharging the battery during the learn cycle. SO essentially, the first learning cycle should be with the full votlage range and correct design capacity afterwards, you can reduce the design capacity to reflect the value you will be using in your application. Same with the voltage, if you don't plan to charge the cells to the max

    I hope this helps.

    thanks
    Onyx