BQ78350: RSOC 100%, ASOC 0%

Hello Spencer,

Many factors can affect FCC. Most common are:

1-  Internal Resistance of the Cell increases. (This can be due to change in temperature or cell degradation)
2- Load - sometimes if the load is big (e.g. greater than 2A)

Was the cell matched to one of the ChemID in our database? How did they obtain the OCV table? Did they use the GPCCHEM tool?

If temperature is a changing factor, was the gauge compensated for temperature? Did they use the GPCCEDV tool?

For how long have these packs been in the field?

Please provide a log file and settings to further analyze this behavior.

Regards,
Jose Couso

Hello Jose,

The chem ID was matched. The packs were only a couple months old. In most cases, FCC dropped to 0 in use, but learned capacity was OK.

Could a large load change FCC to 0 (maybe due to a large enough voltage drop), but leave learned capacity unchanged? I think there is a limit on how much learned capacity can change at any given cycle. Does the limit also apply to FCC? 

According to the tech reference guide SLUUBD3E (17.15, 17.16), ASOC is referenced to the design capacity and RSOC is referenced to the FCC. On these packs RSOC is 100% and ASOC 0%. Could these be reversed?

Thanks,

Spencer

Hello Spencer,

The learned FCC capacity will update at the end of the discharge cycle. It will not change during discharge.

Is temperature a factor here? Does the application requires temperature compensation? FCC is predicted based on load and temperature.

Please share a log file where the FCC behavior can be seen. There's little I can do without this.

Also, please share the gg file. Section 1.2.1 Gauge Configurations Using BQSTUDIO from the Start Guide for BQ Products explains how to export gg file (configuration).

Please share the matched ChemID report.

Please see this Thread for RSOC vs ASOC.

Regards,
Jose Couso

I will have to try and reproduce this in our lab. The customer was not running a log file while using the battery.

My question was if FCC would update to 0 during use if a large current pulled the voltage down low enough to look like the end of discharge. Sorry, I wasn't very clear. Can FCC jump from ~4900 mAh to 0 mAh in one cycle? 

I think I get the ASOC vs RSOC readings. ASOC is 0% with respect to design capacity and remaining capacity is 0. RSOC is 100% with respect to FCC because 0 mAh remaining capacity is 100% of 0 mAh FCC.

Temperature compensation is not enabled on these packs.

Most of the packs are running fine. I just have a couple that had this problem. 

Thanks,

Spencer

Hello Spencer,

Spencer Poff said:

My question was if FCC would update to 0 during use if a large current pulled the voltage down low enough to look like the end of discharge. Sorry, I wasn't very clear. Can FCC jump from ~4900 mAh to 0 mAh in one cycle?

Yes, this can happen. Usually it happens when the internal resistance is too high (low temperatures or aging) OR when there's a big load and it causes the loaded voltage to go below end of discharge voltage. This is a rare case, I need to see exactly what happened. 

You mentioned the ChemID was matched, do you have the ChemID-report and the chosen ID? Please share the configuration file as well.

Spencer Poff said:

Temperature compensation is not enabled on these packs.

It would be good to know if the packs with this problem were ran at different temperatures, specially low temperatures.

Regards,
Jose Couso