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help with bq20z80Av1.10 first learning discharge cycle

Paul K.
Prodigy 160 points

Hello,

I am in the middle of my first learning cycle on a new battery pack using the bq20z80Av1.10.  I started with my battery pack fully relaxed, and at "terminate voltage" (around 3.0V per cell), and finished charging the pack to full.  After letting the cells relax for over an hour now, in the data flash class "gas gauging", Update Status has changed to 05, Qmax (and the Qcells) have been updated, as they were supposed to.

Moving on the the first discharge cycle, I will be using a discharge current of roughly C/5.  So my question here is:  does this discharge current need to be continuous?  What I mean is, do I have to stop discharging, so disconnect my load, every 11% DOD (and 3% DOD, when SOC is below 10%) to let the pack relax in order for the Ra tables to update?  Or just keep the load connected, and only disconnect the applied load (i.e. stop discharging) when terminate voltage is reached?

thanks!

  • 0
    TI__Genius 10235 points

    The discharge cycle should be continuous all the way down to the Terminate Voltage. There is no need to stop at every grid point.

  • 0 in reply to Chase7071949597
    Prodigy 160 points

    Thank you for your prompt response, Chase.

    Is there any issue(s) in adding these relaxation times at every grid-point?

    In my current design (which I am in the middle of running the first few learning cycles), and there have been no updates in the R_a tables when discharging (both continuously and with rest-times at every grid-point) at around C/5 (where C here is 1900mAh).  However, if I increase the rate of discharge from C/5 to somewhere between C/4 to C/3, R_a tables do indeed update - and here I'm continuously discharging. 

    I have read in bq20z80Av110 app-notes and on some e2e forums that when running the first learning cycles to keep the discharge rate around C/5.  Is a lower discharge rate preferred?  Is there a limit to the rate of discharge I should be using?  What can happen if "too high" a discharge rate is used in the learning cycles?  A quick background note, in this design, my battery's chemistry is fairly close to your chemistry selection ID 0116 (going by the cell manufacturer's specifications).

    Thank you for your help,

  • 0 in reply to Paul K.
    TI__Genius 10235 points

    Adding the relaxation periods at each grid point will likely cause some problems with the Ra values themselves. The relaxation points will also prevent Qmax from updating.

    The main limitation with load size is to make sure that it is greather than C/10.  If the load is smaller than that, Ra updates will be prevented.  A good load range is between C/2 and C/5.