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Battery Management - Gas Gauge Forum
Recalibration of bq20z65
Because the CF flag was set we try to recalibrate teh bq20z65 in our battery according your recommendation which I had found in this forum.
1. Charge battery to full
2. Let it relax for min 2 hours
3. Discharge battery to empty
4. Let it relax for about 5 hours
We logged the register of the bq20z65 after step 4 for about 90hours with the EV2300 and the evaluation software.
But the Max Error was still at 6% and the CF Flag = 1.
After we charge the battery to full again after step 4 and let it relax after end of charge we have observed that the CF flag was cleared and MaxError goes back to 1% after further 40 minutes.
Is this a normal behaviour?
How we can speed up a recalibration?
Thank you for your help
The Max Error should have changed to 1% during step 4. Something must have disqualified a Qmax update in either step 3 or 4. It looks like you did get it to update eventually, though, so that's good.
Depending on your chemistry ID, you might be able to update Qmax a little quicker. Qmax update requires 2 OCV points and at least a 37% change in capacity between those OCV readings. So, for example, you could charge to full, rest for 2 hours, discharge to 60%, and then rest for 5 hours. Qmax should update sometime during that 5 hour rest. However, Qmax updates are disqualified if one of the OCV points is taken while in the flat region of the OCV curve. So, this is why it depends on the chemistry ID. If you let me know the chem ID you are using I can give you the flat region voltage and SOC range.
Thank you for your fast repsonse.
The chemistry ID of the using cells is 247 and 309.
For testing the recalibration method I set the cycle counter manually to 100 for producing the "MaxError" failure and to set the CF Flag.
Maybe this has an influence of the behaviour which I had described.
And could you please explain me when the MaxError will be increment with 0.5% and when not?
If I've understood it correct this counter will be incremented if no relaxation time between charge and discharge is present during normal using.
Thanks and best regards
Thank you for your fast response
The chemistry ID of our cells is 247 and 309.
To produce the "MaX Error" failure and to set the CF-Flag I've set the cycle counter manually to 100.
Maybe this has an influence of the behaviour which I've described.
And could you please explain me when the MaxError will be incremented with 0.5% after a cycle and when not?
If I've understood it correct this incrementation can be prevent if a relaxation time after charge and discharge is present under normal using.
Thank you for your fast responseThe chemistry ID of our cells is 247 and 309.To produce the "MaX Error" failure and to set the CF-Flag I've set the cycle counter manually to 100.Maybe this has an influence of the behaviour which I've described.And could you please explain me when the MaxError will be incremented with 0.5% after a cycle and when not?If I've understood it correct this incrementation can be prevent if a relaxation time after charge and discharge is present under normal using.Thanks and best regardsDietmar
The Qmax disqualification region for ID 247 is 3589mV to 3641mV, which is about 30% to 47% SOC. For ID 309 it is 3736mV to 3799mV, which is about 20% to 42%. This should allow you to get a Qmax update by following the shortened procedure I gave you earlier.
Max Error will increment by 1% for every 20 cycles it goes without a Qmax update.
I've some further questions regarding Qmax update procedure.
1. Is it possible to become two OCV measurement points if we charge the battery from SOC=20% to SOC=60% and after relaxation time from SCOC=60% to SCOC=100%?
2. Is the 37% change of charge required between two OCV measurements in both directions?
- Discharge from 100% to 60%
- Charge from 60% to 100% or is it possible to charge only to 80%?
3. Could I detect a proper OCV reading on the VOK-flag to reduce calibration time?
Thanks a lot for your help
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