• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 339 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ40Z60: Valid EOC on the BQ40Z60

Robert Ploeg
Prodigy 240 points
Part Number: BQ40Z60
Other Parts Discussed in Thread: BQSTUDIO

Hi,

We have the BQ40Z60 in production for a 4S6P pack with a max capacity of 20Ah (2.5V - 4.2V). I have limited the capacity and use only 3000mV - 3970mV, giving me approximate 13.5Ah.

The charging voltage at 3970mV, charge termination voltage is 50mV and charge term temper current 250mA.

High voltage charging is from 3900mV @ 2000mA

The COV is set at 3975. 

Sometimes, during tests, I see on a particular board, the COV is flagged before a valid EOC. There is a cell-imbalance at that moment of approximate 15mV. This particular board will constantly have the COV flagged before a valid EOC.

Other boards, same production batch, do not have this issue. They all have the same srec-file. I've extracted a srec-file from a correct functioning battery and programmed this, calibrated cell- and battery-voltage with bqStudio, without any effect. Again hidding COV instead of a valid EOC.

Any idea what could be the cause of this and how I can solve this? 

Thanks,

Rob

  • 0
    TI__Mastermind 42535 points

    Hi Robert,

    If any of the cells hits a higher voltage than what's set for COV, you will get COV triggered. That's how the protection works. As far as balancing goes, once your voltage and RSOC thresholds are met, you will have balancing function as expected. However, the balance timers are calculated based on DOD, so, given that you are not using a full DOD scale, it may be possible that cell balancing might not be as effective as possible. Then again, this could be a one off, where the one cell is weaker than the other or has a bad tab. If either of those abnormalities are present, the terminal voltage can increase quickly causing an imbalance.

  • 0 in reply to Batt
    Prodigy 240 points

    Hi Batt,

    I understand why the COV gets triggered, the problem is why this string gets to that voltage level. In Other packs with approximate same tolerances, the charge current starts dropping earlier so the voltage level of the strings do not hit the charge voltage (3970mV) so never hit the COV (3975mV). 

    It acts like the charge voltage is set higher than the COV. This is what is bothering me.

    Thanks,

    Rob

  • 0 in reply to Robert Ploeg
    TI__Mastermind 42535 points

    Hi Robert,

    The charging will continue depending on the pack voltage first. So, if the pack voltages are checked, then the cell voltage is checked. If the cells are in imbalance the charging will continue until one is in COV. After that the protection will be triggered.

  • 0 in reply to Batt
    Prodigy 240 points

    Hi Batt,

    thanks. I will double check this with other packs and electronics.

    Best regards,

    Rob

  • 0 in reply to Batt
    Prodigy 240 points

    Hi Batt,

    I've checked the same pack with a another electronics board from the same batch. Copied the settings into the new board. Calibrated Cell1 and battery voltage.

    With this electronics the battery charges to EoC completely. Even though there is a measured cell-imbalance of approximate 17mV when charging with 2A (Cell1 is during charging higher compared to 2-4). With the charging  to 3970mV, the charge current starts to roll off when the cells are approximate 3910mV. Cell1 reaches a max of 3974 but slowly drops off again due too lower charge current.

    In the first board the charge current started to roll off at a higher voltage level, as a result Cell1 hit the COV (3975mV) at a charge current off approximate 1.9A.

    What is causing this difference?

    Thanks,

    Rob

  • 0 in reply to Robert Ploeg
    TI__Mastermind 42535 points

    Hi Rob,

    It might be a problem with the components in the other circuit. The gauge by itself only reacts to the input parameters it sees. If any of the active or passive components affects the inputs, this will in turn affect the gauge. So, it might be better to check the board.