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BQ35100: SOH value decays to 0% in a few hours...should take a few months

Matthew Becker
Prodigy 60 points
Part Number: BQ35100

Hello,

We are using the BQ35100 in a new product in order to gauge a primary battery pack that is made up of two Tadiran TL5930 cells in parallel.

The cell chemistry is LiSOCl2 and we are using CHEM ID = 0607 based on the default BQ35100 image v1.02 bld10.

We have been able to successfully calibrate the chip in voltage & current and we can generally communicate with it.

When initializing a new battery, the SOH value initializes to some reasonable value, around ~98%.

However, the SOH value gradually decays to 0% after a few hours...yet the load actually takes a few months to drain the batteries.

Why does the SOH value decay so rapidly?

The load on the battery pack contains pulses and sleep states, so generally it has a large AC component to it. I'm not sure if this is a problem.

Are there load and time requirements for the GAUGE START and GAUGE STOP commands in order for the BQ35100 to accurately measure SOH?

  • For example, does the load need to be a DC load while the BQ35100 is taking a reading?
  • If so, is there a recommended load to use (1 mA, 10 mA, 100 mA)?
  • How much time does the gauge need to be ON in order to get an accurate reading?
  • Does the DC load need to be applied before the GAUGE START command is given?
  • Does the load need to be removed and the cell allowed to relax before issuing the GAUGE STOP command? If so, how long does it need to relax?

Or is this problem due to some other issue altogether?

The following post lead me in this direction, however, I am not sure if this is the same problem.

https://e2e.ti.com/support/power_management/battery_management/f/180/p/566116/2080314?tisearch=e2e-quicksearch&keymatch=bq35100#2080314

Thanks in advance for the help,

Matt

  • 0
    TI__Genius 10370 points

    Matt,

    For LiSOCL2 cells I would suspect/expect you have the gauge configured in EOS mode. For this mode the procedure to follow for gauging would be

    1) Set GE pin high to turn on gauge

    2) Send gauge start command

    3) Apply pulse load. Sampling is done every 8mS therefor it is recommended the pulse length be a minimum of 3-5 samples. Current amplitude should not be an issue. it is required to be a pulse of greater magnitude than the base current. The goal is to see an IR drop to get a sufficient impedance measurement. 

    4) Send gauge stop command once load has completed

    5) Wait for G-Done bit signaling gauge is done with its calculations. 

    6) Read information from the gauge as needed

    7) Set GE pin low to turn gauge off

    Please let me know any follow up questions you might have. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 60 points

    Thanks, Eric.
    What should the procedure be when issuing the New Battery command?
    We are following the procedure you have outlined.
    However, it seems that when we issue the New Battery command, the G-done bit will never set again unless we toggle the GE pin.
    Are we required to toggle the GE pin after a New Battery command has been issued?
    Also, does TI have any example application code they can share on how to use this chip? 
    Thanks again,
    Matt