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bq27500: CC threshold versus Li-ion battery charged to 4.1V

user3793349
Prodigy 190 points
Part Number: BQ27500
Other Parts Discussed in Thread: BQ27510,

Hi,

I'am trying to clarify the following questions:

Our battery pack specs 4.2V with 50mA taper for full charge and 2.75V cutoff for Discharge. The customer wants to charge the battery to 4.1V to extend its cycle life. It seems that we do the Learn cycle with max charge voltage parameter set to 4.2V and taper current set to 50mA. Then after the learn cycle is done, we change back the max charge voltage to 4.1V and leave the taper currents as is to 50mA. Agree?

Now, the questions are:

1. Since we will only charge to 4.1V, 50mA taper, instead of 4.2V, the SOH might reach max of, say, 80% charge or so, Correct?

2. Now, we want to set the CC Threshold to 70%, ie 1 full cycle completed if battery discharges by 70%. Since, we only charge the battery to 80%, the cycle will increment if it discharges to 10% level (80-70). Is this correct assumption? 

Just trying to make sure what i'm doing makes sense.

  • 0
    TI__Guru* 76230 points
    Hi.

    Yes agree.

    1, correct. SOH will be FCC/ design capacity. After learning is done and you adjust voltage to 4.1V, you can adjust design capacity to the value FCC returns after you send the reset command or you just know with your host that 80% doesn't mean your battery needs replacement since you are charging to 4.1
    2. CC threshold according to the DS is in mAH and not %. The cycle count will increment if the accumuated discharge is > cc threshold.

    On a side note, why are you using the bq27500. This is an old legacy device and we have newer devices with firmware improvements like the bq27510 and the bq27520

    thanks
    Onyx