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78PL114S12 - "FCC" value setup on start?

bob churton
Prodigy 50 points
Other Parts Discussed in Thread: BQWIZARD, BQ2060A, BQ78PL114

 

Hi

I have recently bought a bq78PL114S12 –EVM running FW5000 monitoring 3 18650 cells which have been charge/discharge cycling in the default 3S1P.  All of the functions of the BQwizard look to be working except I cannot get FCC to change above 2400mAhr. I have tried different cell chemistries, design capacities and set up 3S2P pack configuration but FCC never goes higher than 2400mAhr.  Surely if you specify 2P or design capacity set at 4800mA then one might expect FCC to start at 4800mAhr (following initial setup/relearn). FCC does adjust itself down as expected during chg/disch depending on load etc.  (Qmax is also always 2400mAhr.)  

Other puzzling issues are:  1) Following a charge when CC is set then SMBdata “Fully charged” is set, but once set it never clears again even when battery discharges to when DC is set.  2) When DC sets and discharge FET is switched off I never get SMBdata “Fully Discharged” go green.  3) When I set up 4S1P pack configuration FCC stayed at 0 and Qmax for cell 4 (only) also was 0.  I was recording voltage from cell 4 and parameters have always looked correct ie pack configuration being shown as expected. 

All of the above makes me think either I have missed a key point or perhaps the 78PL114 within the EVM is not fully functional.  I have read all the application notes/documents.  I have been all around the functions of BQ wizard including logging to see what is available.  The only thing I have not yet done is set up a (.AUX) file which I don’t think I need yet to just evaluate the system.

So if I have 4 18650E batteries in parallel (2550mAhr x 4) how do I set up wizard to set FCC (initially) to be 10200 mAHr?  Running the BQ2060A EVM software one is able to program a "last discharge capcity" figure into the EEPROM.  Can you do similar with the 78PL114?

Any help/suggestions gratefully received. Deadline looming!

Thanks, Bob

 

  • 0
    TI__Guru 73830 points

    Bob, 

    It does look like something is not setup correctly. Can you dump the pack parameters and send them to me? Using bqWizard, go to File >> Save Pack Parameters >> All parameters.

    Thanks

    Tom

  • 0 in reply to ThomasCosby
    Prodigy 50 points

    Hi Tom

    Thanks very much for replying to my enquiry.

    I attach a couple of data files: one for default 3S1P and another for a pack configuration 4S2P.

    I had several queries in my post but my priority is to be able to set up FCC on powerup/initialization and understand how FCC is setup.  Ie what sets it to 2400mA in 3S1P?

    In the 4S2P file please note that FCC = 0 and Qmax = 0 for cell 4, which I referred to in my post (also most voltage settings such as POV are set for 3S and not 4S) but data also shows 4 cells in series and 2 parallel have been recorded. What has changed FCC from 2400 to 0?  I appreciate FCC is updated at various occasions but it is the initial setup that has me confused.

    Most grateful for help!

    regards, Bob

    Just tried to attach 2 files and it seems to be I am allowed to attach only one (3S1P), I shall replay again with 4S2P file if I can!

     

     

     

     

    BC3S1PdefDATA1303.xls
  • 0 in reply to bob churton
    Prodigy 50 points

    Tom

    4S2P file attached I hope

    Bob

     

    BC4S2Pdata1303.xls
  • 0 in reply to bob churton
    TI__Guru 73830 points

    Bob,

    You will need to set the Design Capacity to the combined capacity for the number of cells in parallel. The device should pull this value into the FCC starting point and try to estimate an FCC based on the information in the cell data. You will probably have to go through a learning cycle to update the Qmax estimate in the cell data. Have you done this yet? The device can then make an accurate FCC estimate and Remaining Capacity estimate.

    Regards
    Tom

  • 0 in reply to ThomasCosby
    Prodigy 50 points

    Hi Tom

    Entering a combined figure in Design Capacity has no effect on FCC (still zero for 4S2P pack configuration). What would you define as a "learned cycle"?  I have charge/discharged cycled 18650's with no apparent success which from what I understand from the tech manual should allow a "learn update". Perhaps I am not reaching a particular setpoint?  What I have noticed is that when discharged and DC goes red The SMBus data "Fully discharged" flag has not been set. Might this signify something?

    Regards

    Bob

     

  • 0 in reply to bob churton
    TI__Guru 73830 points
    Bob, You mentioned earlier that there are four cells in parallel and later that there are two cells in parallel. Is the tmap setup for the proper cell configuration? You also mentioned that you tried several ChemID files and are using 18650E cells. Is the ChemID setup for the cells that you at using? We have an applications report - Chemistry Selection for bq78PL114 that describes the profile required to create an aux file. The aux file generation is a critical part of the learning process. The aux file provides the device with a Qmax estimate and Ra-table for the pack and it can be used to program additional packs. The device will then use this information as a starting point for additional Qmax and Ra-table updates during operational learning cycles. These are when you charge the pack, rest for a couple of hours, discharge and rest again for a couple of hours. Qmax will update during the rest period. If you choose to skip the aux file generation process, then the device will try to update Qmax and the Ra-table during the charge / discharge cycles, but the initial estimate may not be close enough to provide a good update. Make sure the you get CC and DC flags following the charge and discharge cycles, respectively. Usually, we find that the user does not get a flag or does not rest long enough when Qmax updates do not occur. I hope that this helps. Tom
  • 0 in reply to ThomasCosby
    Prodigy 50 points

    Tom

    Apologies if some confusion on my part but can confirm 4 in series, 2 in parallel.   Pretty sure Tmap configuration is correct and I am using the correct Chem file but will re-check. I have copy of the Chemistry Selection application notes and by the sound of your comments clearly the aux file is more important than I realised and I shall do one this week. Definitely did not do  "rest periods" in my charge/discharge cycling. Will keep you posted. Thanks for continued assistance. 

    regards Bob