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Original question:

BQ34Z100-G1: inaccurate measurement of the battery

BQ34Z100-G1: inaccurate measurement of the battery over time

Shai Berman
Mastermind 7405 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100, GPCCHEM

Hi Team,

I have a general question about the use case of measurement a two pack of batteries with one power source (charger):
my customer has 2 chargeable Li-Ion battery 10S4P in the system, On each battery pack, they use BQ34z100-G1 & Protection and Balancing solution.

Each battery have 4 wires of PACK+, PACK- and 2 wire of data, they connect the VCC & GND in parallel because they have 1 charger.
On each battery has a golden file and works fine alone but once they connected 2 batteries in parallel they see that after some time one battery voltage is 4.2v while the other is 3.8v and the fuel gauge does not give the correct % results.

Do you see any issue to connecting two individual battery packs in parallel as I mention above?
What do you suggest in order to solve it?

in the attached, you can find GG in .srec format of the battery pack.

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/PCM_2D00_10s10.7z

Looking forward to your response, thanks in advance.

Kind regards,

Shai

  • 0
    TI__Mastermind 42535 points
    Shai,

    No 2 cells are identical. Each cell even from the same manufacturing line has a different characteristic resistance. Therefore one cell in a 2p pack can be weaker than the other. When discharged the weaker cell has a tendency to lose terminal voltage more than the stronger cell. To make things worse, the weaker cell will also have a higher resistance to charging. Therefore it will hold less capacity than the stronger cell. Here you have a10s4p pack. So the effect of such a discrepancy can be more. It will also be seen more during dsg at low RSOCs. So what you see is expected. However, to prevent this from badly affecting the cells involved, we need to use cell balancing. Balancing can be done in both chg and rest. For your application, I would suggest that you use aggressive balancing to minimize the effect of this. Other than that, as far as usage goes, I don't see a problem with charging both cells in parallel. Your stronger cell will most likely take greater charge while the other weaker cell will saturate chg term voltage quicker.
  • 0 in reply to Batt
    Mastermind 7405 points

    Batt Hello,

    Your above description is very generic - there is any case do you know what is the expected delta? 

    if the total difference is less than 1V out of 42V - it would be OK, if more what are the recommendations?

    moreover - what is the recommended solution and how they overcome it in the S10P4?

     

    another issue -  the customer has noticed that the battery reading of SOC is not correct and the charging takes a lot of time.

    please find below attached two charging logs and you can see how the SOC reaches 76% it jumps to 100% and also the current charging drops before time.

    6712.bat1.xls4784.bat2.xls

    please advise what can cause this issue and how we can solve it, you can find GG in .srec format of the battery pack in the link below

    https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/PCM_2D00_10s10.7z 

     

    Thanks

    BR

    Shai

  • 0 in reply to Shai Berman
    TI__Mastermind 42535 points

    Shai, it is not possible to tell you what the voltage delta would be. Across the stack your stronger pack will allow more charge to be pulled from it. So, it will keep up the terminal voltage depending on the load. In either case you need your pack balanced. The bq34z100 does not provide cell balancing. You will need a solution for that.

    Looking at your logs is going to take some time. Please expect to hear back from me by next Monday or earlier.

  • 0 in reply to Batt
    Mastermind 7405 points

    Okay, Thanks.

    Shai

  • 0 in reply to Shai Berman
    TI__Mastermind 42535 points

    Hi Shai,

    Looking at your logs, the jump in RSOC is because of charge termination. When that happens, if FC=-1% is set, you will get jump in RM and therefore RSOC will change.

    It appears to me that you may need to use GPCCHEM to get the correct chem ID and run a learning cycle