BQ35100: Measured impedance stuck at 32767 mOhm

Hi Ashare,

Are you in EOS mode?

Can you provide more information on your battery? Impedance is closely related to battery chemistry.

What ChemID are you using?

Regards,

Evan

HI Evan,

Battery Model - SAFT LS14500

Chem ID - 0623

Gauging Mode - EOS

Measured Z and Scaled R values are plotted in the attached graph. You can see that it saturates at 32767 mOhm. The gauge did not update the measured Z and scaled R values after the EOS was flagged.

Regards,

ashare

Hello Ashare, 

Evan is currently out of office, please expect a delayed response. 

Regards, 

Jonny. 

Hi Ashare,

What was the measured impedance before the EOS flag was set?

Is the EOS flag setting as expected?

Can you share your .gg file and .log file of the discharge?

Regards,

Evan

Hi Evan,

The flag was being set as per the trend detection setting of 20%, which seems to be fine. I am attaching the log file (.xlsx) and the .gg (.csv) files for your reference.

/cfs-file/__key/communityserver-discussions-components-files/196/LS14500_5F00_gauge_5F00_params_5F00_after_5F00_test.gg.csv

/cfs-file/__key/communityserver-discussions-components-files/196/EOS_5F00_Triggered.xlsx

After I observed the constant measured Z values, I let the battery rest for a long period (>48 hrs) and restarted the test. Initially the battery started with a lower measured Z and corresponding scaled R values, but within 2 measurements, it quickly jumped to the high values previously observed and then saturated again at the 32767 mOhm for measured Z which prompted me to think if the internal register is indeed limited to that number. However as per TRM, it is 16 bits long.

Hi Ashare,

Just to clarify the gauge is functioning as expected, the EOS flag is setting as expected. The issue is the Impedance value continues to rise after the flag is set to larger value but is not causing any direct issues in your system. 

If I understand correctly, please allow me some time to check what the max value allowed in the code is. If I am wrong, please correct my misunderstanding.

Regards,

Evan

You are right. The impedance value rising after the EOS being set and the value being saturated at 32767 mOhm are not causing any issue for the battery sample I tested. I am worried that since the EOS flag is getting set almost at the same time when the measured Z hits 32767 mOhm, there is a possibility that for a different sample, the short term trend value may surpass long term trend value (by 20%) at a higher measured Z. I fear that if the system cannot process values higher than 32767 mOhm, the detection process might fail.

Hi Evan,

Evan said:

The max value for Impedance (measuredZ) is 65535 (16 bits).

Have you already confirmed this after cross-checking with the max value allowed in the code?

Evan said:

I can confirm that this condition is being met. Please see screenshot of the trend averages read using EV2400 below:

However, my concern is the reduced max limit of measured Z values that my system is reading. Although the EOS flag is set based on trend average values, aren't trend averages ultimately derived from measured Z? We know that measured Z is temperature dependent which means that there is a possibility that the EOS flag is set at values above 32767 mOhm. My system and the EV2400 are currently unable to read values above 32767 mOhm. If that's the case, there is a possibility that at a different temperature or with a different battery sample, the EOS is never triggered. Is my concern valid?

Hi Ashare,

I quickly scanned the code yesterday because I was quite busy and thought the measuredZ was defined as a16 bits. However, after taking a closer look today I believe you may be correct. I am following up with the firmware team for clarification and confirmation.

Regards,

Evan

Will you be updating this thread (so that I am notified) when the bug is fixed?

Hi Ashare,

There is not a bug but simply a documentation error. It will be fixed when the document is refreshed.

Regards,

Evan

What purpose does it serve for the measured Z and scaled R values to be declared as a signed integer? They never go negative anyways. If we were to assume that it is indeed limited to 32767 mOhms then how do I address this issue I highlighted in my earlier post? I have highlighted it below:

ashare said:

I am worried that since the EOS flag is getting set almost at the same time when the measured Z hits 32767 mOhm, there is a possibility that for a different sample, the short term trend value may surpass long term trend value (by 20%) at a higher measured Z. I fear that if the system cannot process values higher than 32767 mOhm, the detection process might fail.

Regards,

Ashare

Hi Ashare,

Please share a log file of the EOS flag setting incorrectly.

Regards,

Evan

Hi Evan,

I am not saying that in the test that I conducted, the EOS flag is being set incorrectly. It is getting set when the measured impedance is 32767 mOhm. What I am worried is if I use a different sample of the same battery, the moving average filter that detects the sharp rise in the impedance could trigger at different levels of the measured impedance (i.e. < 32767 mOhm or > 32767 mOhm), but the system cannot detect more than 32767 mOhm. If so, isn't there a possibility that the EOS flag is never set? For e.g. couldn't there be a case where the short trend average surpasses the long trend average by 20% (condition for EOS flag setting) at 32768 mOhm (undetectable due to system limitation) of measured impedance? 

Regards,

Ashare 

Hi,

Please allow me some time to look into this.

Thanks,

Evan

Hi,

I have notified the FW team and they will address this at their earliest convenience.

Thanks,

Evan