BQ40Z80: Cell Balancing during Rest and Charge Mode

Minh Nguyen

Part Number: BQ40Z80
Other Parts Discussed in Thread: GPCCHEM, , BQ40Z50, BQ34Z100-R2

Hi,

I was able to get a Golden File with a complete gas gauging cycle for CB activation.

I am trying to predictably use the Charge Mode and Relax Mode cell Balancing. So far the only way I can get CB to work is by RESET and CB turns on but will shut off after about 5 minutes, most like due to the Relax Balance Interval set at 300s.

What would be the best way to get CB to activate when pack is sitting idle regardless of SOC? I can see that after RESET, the balancing time populates and with a current applied to the Pack, CB stays on which is probably CHARGE mode CB. But after taking off current off, CB goes off.

Any help would be greatly appreciated,

Minh

over 2 years ago

0 Wyatt Keller over 2 years ago

TI__Guru** 105770 points

Hello Minh,

Please review out FAQ page for additional details we need to help you debug: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1127899/faq-bq40z80-faqs?tisearch=e2e-sitesearch&keymatch=faq%3Atrue

We will need the log and .gg file in order to see what conditions the gauge sees. Cell balancing is only enabled after a field Qmax update has occurred, and if the delta capacity between cells is low the gauge will disable cell balancing.

Sincerely,

Wyatt Keller

0 Minh Nguyen over 2 years ago in reply to Wyatt Keller

Prodigy 40 points

Hi Wyatt, RECHARGEABLE_2023_04_24.gg.csv For_TI_Balancing.log

Please see attached for log and gg. file.

It was also my understanding that the point of a Golden File (SREC) with Learning Cycle completed would fulfill the Qmax update for subsequence packs built.

Thank You,

Minh

0 Wyatt Keller over 2 years ago in reply to Minh Nguyen

TI__Guru** 105770 points

Hello Minh,

From the log it looks like LStatus is 14 which indicates cell balancing should be enabled since a field Qmax has occurred. Looking at the CB DOD points they are very close to each other, I'm not sure if it even qualifies to start cell balancing, if you purposefully unbalance the cells will the cell balancing trigger after performing one cycle?

Sincerely,

Wyatt Keller

0 Minh Nguyen over 2 years ago in reply to Wyatt Keller

Prodigy 40 points

Hey Wyatt,

I haven't tried to manually unbalanced the cell to further test the CB function. I was assuming that if the Min Start Balance Delta (10mV) hits, CB activate. But from what you are telling me, the CB D0D overrides that?

I'd also like to point out that I did perform the learning cycle but I have used the defaulted chem ID, (1210). Would that natively cause CB function to be sporadic and not working as intended?

A separate issue that I am getting, which might be due to the default chem ID, my SOC is 99% but cells are only about 3.8V (Qmax should be above 10000mah) so we are no where near the top. As a result, the CHG FET keep disabling.

Thank You,

Minh

0 Wyatt Keller over 2 years ago in reply to Minh Nguyen

TI__Guru** 105770 points

Hello Minh,

If you have not matched the chem ID using GPCCHEM or an exact match of the model then you will need to upload the correct chem ID and re-run learning. Using the default chem ID when it does not match with your battery can cause multiple issues with gauging, including the cell balancing. Are you trying to use voltage based balancing or dQ based balancing?

Sincerely,

Wyatt Keller

0 Minh Nguyen over 2 years ago in reply to Wyatt Keller

Prodigy 40 points

Hi Wyatt,

Ideally we would like to use voltage based balancing.

We have previously tried to use the GPCHEM tool and it came back with ID 5797 with 3% deviation. We have tried to run a learning cycle on that but was unable to reach the required 90% DOD, our FC flag never triggered so we couldn't mark the top. We since had to resorted back to default CHEM to complete the learning cycle.

Could this be a bug with that particular CHEM ID preventing us from doing the learning cycle?

We are running Li-on 9500 mAh cells.

Thank You,

Minh

0 Wyatt Keller over 2 years ago in reply to Minh Nguyen

TI__Guru** 105770 points

Hello Minh,

Sorry for the misunderstanding, dQ is the most common balancing so I was under the impression it was dQ balancing. That should be mostly voltage based criteria to start balancing.

Were you able to capture the learning cycle logs using chem ID 5797? When you do learning you must cycle the full range of the battery specification, not your application voltage range. After learning you can decrease the voltage range.

Sincerely,

Wyatt Keller

0 Minh Nguyen over 2 years ago in reply to Wyatt Keller

Prodigy 40 points

Wyatt,

Please don't be sorry, we're happy that we are getting great feed back from you. In our Advanced Charge Algorithm menu, there is the only option to balance with dV in Cell Balancing Config.

Yes we did log the cycles. Please see attached. Step One is initial Charge, Step Two is Discharge, Step Three is Charge, and Step Four is Discharge. We were unable to get the LStatus to move forward at all those steps, it stayed at 4. For some reason the pack is at REST but no Qmax data point is being record.

7532.4890-005_Discharge_GoldenFile_Step_Two.log 7416.4890-005_Charge_GoldenFile_Step_Three.log 8284.4890-005_Discharge_GoldenFile_Step_Four.log 6523.4890-005_Charge_GoldenFile_Step_One.log

Thank You.

Minh

0 Wyatt Keller over 2 years ago in reply to Minh Nguyen

TI__Guru** 105770 points

Hello Minh,

I will look into your logs by the end of today.

Sincerely,

Wyatt Keller

0 Wyatt Keller over 2 years ago in reply to Wyatt Keller

TI__Guru** 105770 points

Hello Minh,

The BQ40Z80 does not support voltage based cell balancing, this is only support in the newer BQ40Z50 firmware releases. Make sure to check the TRM for the functionality you are trying to implement. The BQ40Z80 does not support 7S for new designs, we recommend using the BQ34Z100-R2 along with monitor for the BMS solution.

Sincerely,

Wyatt Keller

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BQ40Z80: Cell Balancing during Rest and Charge Mode