BQ40Z60 - Problem with calculating capacity

Massimiliano De Cristofaro

Other Parts Discussed in Thread: BQ40Z60, BQSTUDIO

Dear team,

a customer of mine has the following problem with the BQ40Z60.

Battery of 4 series accumulators LiFePO4 MHR32113 from A123.

Nominal capacity is 4500 mAh. Full-charged battery voltage is 14,6V. The Charge Current is up to 2А. The Discharge Current is about 80mА. Minimum voltage of a single accumulator is 1,6V. Maximum Temperature is +65 С.

Problem is in a not-correct determination of charge percentage. Voltage of each accumulator is 3339, 3292, 3613, 3354mV, that doesn't correspond to the Charge. Nominal Capacity is 4300-4500mAh. However, there's in the bqStudio shown 1715mAh, and it's considered as a maximum Charge. Probably, it is because of incorrect coefficients applied, determined by the Chemistry Type...

Question: How could I state them in a correct way? In the Table of Accumulators, suggested in the bqStudio, such accumulators are not available.

Could you please advice?

Thanks a lot in advance for your help.

Best regards,
Massimiliano De Cristofaro
Application Support Engineer - Power Management
ASKTEXAS DiamondLane – EMEA Distribution Support
Texas Instruments Deutschland

over 9 years ago

0 Benjamin Lough over 9 years ago

TI__Mastermind 27095 points

Hi Massimiliano,

The gauge relies on an OCV table and resistance table in order to determine full charge capacity. Both of these tables are dependent on the selected chemID. If the chemID is a poor match, you will likely see errors in state of charge, remaining capacity and full charge capacity. Section 7.4 of the TRM might be useful to you: www.ti.com/.../sluua04c.pdf.

As a side note, I would confirm their QMax initial values are set appropriately. If you want to post the gg.csv, I can take a look.

Best Regards,
Ben Lough

0 Massimiliano De Cristofaro over 9 years ago in reply to Benjamin Lough

TI__Expert 6640 points

Hi Ben,

thanks a lot for your help.

I sent this information to the customer and asked for the gg.csv file.

Thanks again.

Best regards,
Massimiliano.

0 Massimiliano De Cristofaro over 9 years ago in reply to Massimiliano De Cristofaro

TI__Expert 6640 points

Hi Ben,

Please find enclosed the gg.csv file.

Could you please take a look?

Thanks a lot in advance.

Best regards,

Massimiliano.

bq40z60_mhr32113.gg.zip

0 Benjamin Lough over 9 years ago in reply to Massimiliano De Cristofaro

TI__Mastermind 27095 points

Hi Massimiliano,

Qmax values looks like it has been set appropriately. Do you know if they have matched a chemID for their battery configuration? . They will need to do this to identify a good chemID match for their battery.

If they have already identified a chemID, I would suggest doing a learning cycle. This will update Qmax and your Ra tables.8816.LearningCycleOverview.pdf

According to the gg.csv file you attached, the device has not done any Qmax or Ra table updates.

Best Regards,

Ben Lough

0 Massimiliano De Cristofaro over 9 years ago in reply to Benjamin Lough

TI__Expert 6640 points

Hi Ben,

thanks a lot for your help.

I sent your answer to the customer.

Thanks again.

Best regards,
Massimiliano.

0 Ivan Knyazev over 9 years ago in reply to Benjamin Lough

Prodigy 10 points

How can I start balance before identification ChemID? I suspect that the battery voltage difference is too large to right identification. I can mistake.

0 Massimiliano De Cristofaro over 9 years ago in reply to Ivan Knyazev

TI__Expert 6640 points

Hi Ben,

Please find below other questions from the customer:

1. I failed to provide a cycle of identification of the chemistry and learning. I've discharged the accumulators, however, charging via the IC doesn't start (even though on one accumulator the voltage fell down up to 1,6V). I had to charge directly, not to harm the accumulators. One more question... how to start up balancing of the accumulators?

2. Another extra question is regarding identification of the chemistry and accumulator balance. Is it important, by which term stopped the charging? I have it stopped due to overloading of one accumulator.

Could you please advice?

Thanks a lot in advance.

Best regards,
Massimiliano.

0 Benjamin Lough over 9 years ago in reply to Massimiliano De Cristofaro

TI__Mastermind 27095 points

Hi Massimiliano,

1. Based on the gg.scv file you attached, you have cell balancing enabled. It looks like your cell balance timers are all 0 however, which would prevent cell balancing. I would try resetting the device. It should calculate the cell balance timers for you. Section 8.4 of the TRM might be useful to you:www.ti.com/.../sluua04c.pdf.

2. For chem Identification, I typically set the charging voltage to what is recommended in the battery datasheet and terminate the charge once the current has fallen below C/50.

Best Regards,
Ben Lough

0 Massimiliano De Cristofaro over 8 years ago in reply to Benjamin Lough

TI__Expert 6640 points

Hi Ben,

thanks a lot for your support.

I sent your answer to the customer.

Thanks again.

Best regards,
Massimiliano.

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BQ40Z60 - Problem with calculating capacity