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BQ35100EVM-795: EOS for LiSOCl EVE_ER34615 (19000mAh) batteries. SOH keep dropping by SOH max delta

Jaga Baga
Prodigy 20 points
Part Number: BQ35100EVM-795
Other Parts Discussed in Thread: BQ35100

Hello!

I amtrying to set up BQ35100 to work with EVE ER34615 batteries in EOS mode. I have set up everything as it was described in technical reference manual and other documents on this site, and after many tries I can't get it to work. SOH keep dropping by SOH max delta. I read multiple threads from other people that have this issue (https://e2e.ti.com/support/power-management/f/196/t/708442?tisearch=e2e-sitesearch&keymatch=bq35100%252525252525252520EOS%252525252525252520not), but all of my efforts have failed.

I have logged some data and exported golden image files (attached). Can you please take a look at them and make sure if all of my settings are correct? 

I believe that my procedure of gauging is correct:

  1. GE
  2. GAUGE_START
  3. APPLY LOAD
  4. WAIT FOR THE LOAD TO END
  5. GAUGE_STOP
  6. Wait until the Gauge calculates the data

Some times I get SOH_MERIT (EOS_MERIT) or EOS_BAD_OCV. At other times no error. I did 18 cycles this last time, but still the SOH kept dropping. 

Data log:

Nr. Measured Z, mOhm Scaled R, mOhm SOH, % Comment
1 3661 3661 98
2 4445 4445 96 SOH_MERIT
3 3996 3996 94 SOH_MERIT
4 4066 4066 92
5 3844 3844 90 SOH_MERIT
6 4485 4485 88
7 4643 4643 86
8 4131 4131 84 SOH_MERIT
9 3700 3700 82 SOH_MERIT
10 4060 4060 80
11 3580 3580 78
12 3521 2542 76 SOH_MERIT
13 3726 2690 74 SOH_MERIT
14 3645 2632 72
15 3862 2788 70 SOH_MERIT
16 3756 2712 68 SOH_MERIT
17 5485 3960 66
18 5265 3801 64 SOH_MERIT

EOS_18cycles_SOHdropping_GoldenImages.zip

  • 0
    TI__Guru* 76230 points

    Hi Jaga

    We will look into this and get back to you within a few days.

    thanks

    Onyx

  • 0
    TI__Genius 10370 points

    Jaga,

    I think a few things might be happening here. 

    First, lets start with the SOH_MERIT that is being triggered. This bit sets when the EOS algorithm fails due to a negative value in the math. The most common reason for this is when GE goes high the gauge takes what is assumed to be an OCV voltage measurement. From there the time it takes to issue the "Gauge start" command if the battery is not relaxed and a higher voltage is detected the algortihm falls down because you cant have a higher voltage than OCV without chg current. I suspect there is not a sufficient rest period between the pulses and the voltage is still relaxing back up in the positive direction. A "hacky" way around this is to enable a small load to keep the voltage from increasing during this phase. You will want this current load as small as possible. 

    Second, lets look at the measured impedance and scaled impedance.  I see the first 11 pulses are the value meaning on the 11th pulse you learn the scale factor. until the scale factor is learned the measuredZ will be used to correlate to the Ra table. The values around 4K put the expected SOH at grid 11/12 which represents close to 10% SOH remaining. After the scale factor is learned you drop the the 2500 Range which is full. This means there is some added resistance/cell to cell variation for your setup (which is the intent of Scale Factor). I suggest manually writing [State of Health] in Datamemory (address 0x4209) back to 100% after the scale factor is learned. I would not issue the "new battery command" because that will set the scale factor back to unleanred. 

    Ra Table

    Lastly, Some early ID's had a complication with the OCV table. Please set the Cell Terminate Voltage to 900mV. There is a boolean check in the firmware to enable the smooth to 0 function and with the TermV above 1000mV it is always triggered. This forces the gauge to drop SOH by max delta every time

    If you have any further questions please let me know

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 20 points

    Hello Eric,

    Thank you for such detailed explanation. I will implement changes suggested and get back to you as soon as I get some results.