bq40z50 Balancing conditions

Roman Buchholz

Other Parts Discussed in Thread: BQ40Z50-R1, BQ40Z50

Balancing starts when directly charging after discharging, without waiting for an OCV Measurement.

Min Rsoc for Balancing is set to 80%, but it already starts balancing at a lower Rsoc. I am Using the bq40z50-R1 Firmware!

over 10 years ago

0 ThomasCosby over 10 years ago

TI__Guru 73830 points

Roman,

Please provide a log file and srec file and we will review the data.

Tom

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

Balancing.xlsx

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

This forum does not allow me to upload the srec file. May I send it to you via mail?

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

Seems like Balancing at rest is not operating in the right way also. CBR in Balancing configuration is set to 1!

After letting the pack rest for more than 5 hours and charging it balanced the cells during charge, but already from the begining of the charge. Rsoc min for Balancing is set to 80%!

after the balancing during charge there were still some misbalancing visiable.

Letting it rest for one night and waiting for balancing at rest did not help, so a small discharge current lead to calculating the new balancing times. Connecting the pack with a charger leads to balancing again.

0 ThomasCosby over 10 years ago in reply to Roman Buchholz

TI__Guru 73830 points

The Min RSOC for Balancing parameter only applies to balancing during Rest. The gauge will balance cells at lower SOC when in Charge mode.The IT gauges only use capacity balancing, although there is a correlation to the cell voltages. We would need to see the capacities for each cell to verify imbalance.

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

Okay I understand that, so everything is as expected. I did not collect data for the Qmax of every cell, but they were slightly different. I will make another measirement tonight with Qmax measurements.

I expected that after balancing in charge therer will be balancing at rest (because OCVs of the cells are different).
In my opinion after charging it rests for a long time so another OCV data is taken and because RSOC is above 80 % it should balance the cells during rest.

0 Roman Buchholz over 10 years ago in reply to Roman Buchholz

Intellectual 355 points

There was an imbalance of almost 100mV, but no OCV measurement was taken, so this imbalance was not cleared.Balancing bei 100mV Im Rest Mode erfolglos.log

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

I made another measurement over night. Balancing 13.log

I am using a low threshold mosfet (DMN2004DWK-7). This should be mentions somewhere in the technical Reference of bq40z50.

as I can see balancing started, but did not finish. So cells are still unbalanced.

I will run another cycle to see if it is still the case after another Qmax update and OCV measurement.

As I use three parallel 82 Ohm resistors as a balancing resistor, I am balancing with a 27Ohm resistor. so the calculated Cell Balancing times are: 80 and 81 seconds. I doubled them because I had to adjust current measurement (dividing by 2).

0 ThomasCosby over 10 years ago in reply to Roman Buchholz

TI__Guru 73830 points

Roman,
I will review the log. Just to confirm, you are using the bq40z50-R1 firmware for these tests? Cell balancing does not work properly with the bq40z50 firmware.
Tom

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

Thomas,

thats right. In another post we talked about it already.
I updated to the new firmware already!

0 ThomasCosby over 10 years ago in reply to Roman Buchholz

TI__Guru 73830 points

Roman,

I reviewed the log file and the balancing times are set properly. Note the DOD points and the balancing times. The larger the DOD value, the shorter the balancing time. Note that the DOD point for Cell 1 is the largest value and this indicates that it was the lowest voltage cell when the DOD point was set. The balancing time should be set to 0 for the highest DOD point and it is in your log file. The log file does not show when the DOD points were set, but the cell voltages for Cells 1, 3 and 4 were fairly close at the beginning of the log. It looks like Cell 4 may be damaged, because the cell voltage increases significantly as compared to the other during charging. This would indicate that the series resistance is higher. It does not look like Cell 2 is charging, so It may be damaged as well.

Tom

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

All cells must be okay, I am Running several cycles every day. My question is: will the balacing at rest recognize and balance an imbalance in higher voltages like

3580, 3400,3600, 3650

down to

-->3400, 3400, 3400, 3400?

0 ThomasCosby over 10 years ago in reply to Roman Buchholz

TI__Guru 73830 points

If the balancing timers are set to balance Cells 1, 3 and 4 and the RSOC is greater than the Min RSOC for Balancing, then the gauge should balance the cells. It will take a long time given the amount of imbalance.

0 Roman Buchholz over 10 years ago in reply to ThomasCosby

Intellectual 355 points

time is not critical in my application. But i need the cells to be balanced, so that the voltages are also balanced.

I made a log of this state already two times, but i could not see any balancing at rest with such an imbalance.

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bq40z50 Balancing conditions