Very strange power pump results

Elman Efendiyev

Other Parts Discussed in Thread: BQWIZARD

Hello!

I testing bq78PL116EVM with 16S 2.4A*h 18650 Li-Ion pack. Pack is unbalanced and made from old cells (this is for testing purpose).

When pumping works i see that lowest voltage cells getting voltage DROP (should be rise, right?) about 1mV/minute even when this cells getting pumps. Another strange thing - i never see "North" or "South" in Cells window Pump column (bqWizard software), only "None" there, but in Cell Balancing tab Net Pump count constantly increases. All logs and screenshot for this issue in attached archive logs.zip pump_normal folder.

Investigating this issue a was suspecting that cell voltage drops due to natural cell leakage and completely disconnected the pack from EVM for 10 hours. Highest cell leakage was about 10mV/hour (about 6 times less tan with EVM attached).

Then a suspected that this leakage due to EVM power consumption (and cell weakness), attached the pack to EVM and disabled Power Pump. In this case voltage drop on weakest cells was almost same (or even less) as with Power Pump enabled, so no result from power pumping at all. All logs and screenshot for this issue in attached archive logs.zip pump_disabled folder.

Then i decided to test if Power Pump works at all, turned on "All Cells South" test pumping mode and see "South" in Cells window Pump column (which a never sought with normal pumping) and Cell 0 voltage rise about 1 mV/second, which i think is fine and want to see such result in normal pumping.

Please tell me how to resolve this issue.

2742.logs.zip

over 13 years ago

0 ThomasCosby over 13 years ago

TI__Guru 73830 points

Elman,

The device will inhibit cell balancing if the voltage imbalance exceeds the Cell Imbalance Fail Voltage. Can you attach the .ppcsv file or a Pack Parameter dump as well?

Regards

Tom

0 Elman Efendiyev over 13 years ago in reply to ThomasCosby

Prodigy 80 points

Tomas,

Cell Imbalance Fail Voltage is 2V, which is more than possible for Li-Ion, and i see balancing active but not effective:

It looks more like passive resistive balancing.

Zipped ppcsv attached

I found that even this non-effective balancing stops after some pack idle time, even when pack is still unbalanced, and started again when connecting a charger. This is strange for me to (you can see the spike - this is when charger connected- balacing restarts and still active after charger disconnectio... for some time..._):

Also i can't find info how to select balance current. Datascheet said it selectable from10mA to 1A by component selection, i suspect this is just inductor value but cand find where this is explicitly defined in documentation.

5658.16cells.zip

0 ThomasCosby over 13 years ago in reply to Elman Efendiyev

TI__Guru 73830 points

Elman,

I tested your setup on my bench and was able to confirm the results. I have found that the device designed to disable cell balancing, if the voltage imbalance is greater than approximately 500mV.

Regards

Tom

0 Elman Efendiyev over 13 years ago in reply to ThomasCosby

Prodigy 80 points

Thanks for info Tom. Is it bug of feature? Can i expect future revisuons to ba able to balance more than 500 mV difference?

Could you please help me with balancing current question:

"Also i can't find info how to select balance current. Datascheet said it selectable from10mA to 1A by component selection, i suspect this is just inductor value but cand find where this is explicitly defined in documentation."?