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BQ40Z60: CV charging mode

Part Number: BQ40Z60
Other Parts Discussed in Thread: GPCCHEM, BQSTUDIO

Hello,

1. I do have a BQ40Z60 EVM and have configured for a 4S1P pack.

The charging current is set @640 mA i.e. 0.2C for a 3200 mAh cell capacity INR18650B Panasonic. 

The calibration is performed initially before working of the pack. The charging current although was 450 mA initially and it drooped to 330 mA in some time. 

Similarly when resetting after 30 mins although the supply current was just 500 mA (now it got automatically increased by some means) the cell current increased to 600 mA. Why is such a behavior happening.

2. Cell-1 reached higher cutoff voltage and the TC is set but why isn't the cell balancing happening to increase the pack behaviour. The cell did charge during this period upto 74%.

Please go through the attached gg.csv file for better lookup Learncycle_BQ40Z60_4S1P_3200mAh_registers.gg.csv

How to resolve the cell balancing issue. How can I be confident that the cell balancing is happening as it is suppose to happen .

 

  • Hello Mihir,

    1)

    Have you performed all the setup as in the users guide for the EVM? https://www.ti.com/lit/ug/sluub71/sluub71.pdf?ts=1591299981972

    What kind of reset are you performing at 30 minutes?

    2)

    I see you have the hex 5 for setup of cell balancing which should be correct for enabling balance while rest and internal resistor balancing. Have you tried reviewing section 8 in the TRM to make sure you meet the criteria for cell balancing? 

    TRM: https://www.ti.com/lit/ug/sluua04d/sluua04d.pdf?ts=1591299878623

    Your minimum delta is set for 3mV to start cell balancing might be too low.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt

    1. The setup has been performed as provided by https://www.ti.com/lit/ug/sluub71/sluub71.pdf?ts=1591299981972, except to the fact that the minimum output voltage (MOV) is set at 8369 corresponding to the formula [MOV = 610*(1 + R1/R2 )  provided in TRM advanced cell balancing algorithm page 57. R1 = 332 kohm and R2 = 26.1 kOhm as provided in the TRM.  Similarly voltage threshold = 32 [610*(1 + R1/R2 ) /256]  this was also provided in TRM. Would this settings matter. 

    2. As you might have seen the gg.csv file the charging current is set @640 mA at all temperatures still the Bq board injects less current on to the battery.

    3. The reset that I'm talking about is a manual reset. 

    4. Yes I've gone through section 8 of TRM for cell balancing and have made changes accordingly, although I need to relook into the minimum delta that I've kept.

    5. Another query is related to current threshold, according to TRM current threshold = 0.39 / R_chg. Now R_chg = 0.01 Ohm making current threshold configuration value = 39. However if I try to tweak this I'm able to vary the current flowing through the battery. Setting it to 33 I'm able to charge the battery with 640mA which is what I've set in the advanced charging algorithm as I mention in point 2. 

  • Hello Waytt,

    Again I did try to charge the cells as you mentioned using the cell calibration manual, TRM. Currently the pack is not able to charge beyond a certain point as the relative SoC of the cell is reaching 100% early where as the absolute SoC of the cell is still @75% . How can I make sure that the full charge capacity of the pack increases as still there is some capacity left in the battery 

    I've attached the jpeg image of cell current for 4S1P pack along with individual cell voltages. Through the figure you will be able to see that the cell  1 and cell 4 have higher charge voltage during charging period where as these have low voltage at discharging duration in comparison to cell 2 and cell 3 voltage

  • Hello Mihir,

    Make sure you have the correct ChemID on your bq40z60, you can use the GPCCHEM tool to match your batteries log and find a chemID. Can you also provide the bqStudio log of the image you shared?

    Sincerely,

    Wyatt Keller

  • Hello Waytt,

    I performed the learning cycle again on the same panasonic cells NCR18650B (3350 mAh) from scratch. In the subsequent reply I'm providing the gg.csv, Log file as well as the matlab generated results for your further analysis.

    These are the observations that I would like to mention so that you will be able to resolve this issue in a better way.

    Observations

    1.  The learn cycle was performed properly. Initially all the cells were balanced by a external supply and kept at 100% SoC level. The gauge enable and reset registers were subsequently updated and the learning cycle started. The RDIS and GAUGE_EN registers were set. 

    2. The cells were discharged completely through a load and then the cells went into CUV at the same time FD was set register were also set during the relax mode. Also the RDIS register became reset in the relax mode. Also REST register got set meaning that the OCV value was successfully obtained

    3.  Now after more than 5 hours of rest after discharging, the cells were now subjected to charging, with the start of charging duration the VOK register got set.

    4. The battery pack charged till around 4.1V approx. Ideally the current set through the advanced gauging algorithm was set at 640 mA during normal charging period and 320 mA during precharge condition. It was observed that for 30 - 45 mins (approx.) of initial charging duration that the cell was getting charged with 486 mA or so instead of 640 mA. Also one interesting aspect is that the cell current in the BQstudio showed lower than 480 mA (approx 340mA) where as the supply is still delivering 480 mA of current. 

    5.  Even the SoC is not getting calculated during the precharge condition although the Qmax update Q gets updated with negative charge value during this duration.

    6.  The FC and TC conditions are never getting met meaning the learning cycle is failing all the time 

    The details of log file, gg.csv file as well as the matlab generated data are 4201.Learncycle_BQ40Z60_4S1P_3200mAh_registers.gg.csvMain_Discharge_09_06_2020_3200mAh.log as follows

     

  • Hello Wyatt,

    I haven't had a response from your end related to the current issue that I'm facing.

    The Qmax update during charging duration is not happening meaning that Qmax 0x05 update never happens 

    causing the learning cycle to fail.

    Can you provide the solution to the same and go through the gg.csv file that I've shared thoroughly so that 

    the issue is resolved early.

    Thank you 

    Regards

    MIhir

  • Hello Wyatt,

    I again thought of performing the pack charging with all the cells within a 4S1P pack (where 1P is equivalent to 10 cells connected in parallel) at equilibrium, while charging there is a 300mV delta between cell1/cell4 w.r.t cell2/cell3 that I'm observing that impacts my charging profile quite a lot. I'm providing the  snapshot of the BQstudio dashboard.

    Eagerly waiting for your response.

    Thanks 

    Mihir

  • Mihir,

    This is a repeat post. Please check what we posted on the other item to resolve your issue.