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Some (very) beginner design questions

Kunzy
Prodigy 50 points
Other Parts Discussed in Thread: BQ2084-V143, BQ76920, BQ29312A, BQ3055, BQ40Z50-R1, BQ78350-R1, GPCCEDV, BQSTUDIO, GPCCHEM, EV2400, MSP430F5529, BQ40Z50

Hello all,

I apologize as I might be asking a bit much of the community, but I want to build a battery pack and have some design requirements and just need some pointers to get the ball rolling.  I have looked around all over TI's website and parts and reviewed a few other threads on here, but still scratching my head.

I would like to build my own battery pack based off of 4 LiFePO4 cells.  The solution does not need to control the charging of the cell as that will be taken care of externally through a CC/CV algorithm on a LTC4020 based solution.

Requirements:
4 series LiFePO4 cells
Cell balancing
Able to sustain 10Amp discharge and (if possible) charge rates
Support voltages 10V - 14V  (this is ideal working range, protection thresholds may differ some)
LED meter for remaining capacity preferred
Interface for external MCU interaction preferred
15Ah capacity
These are the cells I plan to use:  www.headway-headquarters.com/.../

I think that was all my requirements.  I have looked in to the bq2084-v143 and companion part bq29312A.  However, the latter is in the NRND status and am not sure about the compatibility of the bq76920.  Additionally, the datasheet doesn't mention anything about LiePO4 cells, are they compatible?

Again, I am rather new at battery packs and am willing to learn, I just need a little kick-start.  All suggestions are welcome.

  • TI__Guru 73830 points
    We have several options to support LiFePO4 cells. First, you will need to decide whether to use the CEDV or Impedance Track gauging algorithm. A good place to start is at the BMS University website, where you can learn more about these technologies.

    www.ti.com/.../battery-management-bms-university.page

    If you decide to use an IT device, then we recommend the bq40z50-R1. If you want to use a CEDV device that supports LEDs, then the bq3055 may be a good choice. The bq78350-R1 and bq76920 chipset is also a good option to support a 4S configuration.

    We have not characterized the cell that you have selected, so you can collect data and use our online GPCCEDV tool to try to find and acceptable match to a ChemID in our portfolio.

    www.ti.com/.../GPCCHEM
  • in reply to ThomasCosby
    Prodigy 50 points
    Hi Thomas,

    Thanks for the quick reply. I have reviewed a handful of the BMS university videos and that helped a lot.

    I think I will go down the road of using the Impedance Track technology and I am liking what I see with the bq40z50-R1. I do have a few other questions though.

    It looks like bqStudio must use one of TI's adapters to communicate with the IC? I am looking to keep R&D costs low for this project as it is more of a side-project to familiarize myself with battery systems with small hope of entering production (but may enter production depending on how well it works and if I can find a market for it). Is the $50 Thumbus-2300-SMB the only way bqStudio will interface with the IC? Will this adapter work for characterizing the cells for a GPC Chemestry ID or will I need to get either the EV2300 or EV2400 as stated on the GPCCHEM page? Is there an adapter workable with bqStudio based off of one of the MSP430's? I believe I will also need an adapter of some kind for the calibration steps? Sorry for all these questions, I'm kind of cheap.

    I think that will be all my questions for the moment, thanks again for your help.
  • in reply to Kunzy
    TI__Guru 73830 points
    I use the EV2300 or EV2400 with the bq40z50EVM and have not tried the Thumbus-2300. The EVM has the mini USB connector to support the Thumbus, but we have not tried it. I can try it after I return to the office in January.
  • in reply to ThomasCosby
    Prodigy 50 points
    I actually just looked at the EV2400 schematic and found that it uses the MSP430F5529. I have access to a launchpad and think I might be able to just use that. It looks like the firmware update utility for the EV2400 might program the launchpad if I put it in the bootloader mode and use the -s flag. Given that most of the ports on the EV2400 are for future use, I could probably just wire it up.

    Anyway, I really appreciate your help and insights, I think I will carry forward with the design for my battery pack centered around the bq40z50-R1.
  • in reply to Kunzy
    Prodigy 50 points
    Hello again,

    I sat down to try and see if the firmware update utility for the EV2400 would install the firmware onto the MSP430F5529 launchpad but it didn't work. It looks like the firmware update utility relies on some custom BSL code that is not in the device.

    Given that TI has released the schematic and board layout of the EV2400, do you foresee TI releasing the firmware binaries as well? Or at the very lease, the BSL sections needed for running the firmware utility?

    Again, I know it sounds like I am being awful cheap, but this is simply a side project and I can't justify $200 on a tool I will only use once if I don't end up trying to market this product.
  • in reply to Kunzy
    TI__Guru 73830 points
    There is an EV2400 firmware updater on the EV2400 website. You can try using that for your project.
  • in reply to ThomasCosby
    Prodigy 50 points

    Hi,

    Unless I am missing something, the only file I can find is EV2400_Updater_v0018.exe from sluc578. My original thought was to use the -s option and just put the board in the BSL mode. The firmware utility finds the device and attempts to start the process, but it never makes it past performing the mass erase.  And it appears the firmware file is embedded into the EXE. Below is an output of the tool:

    Skipping putting EV2400 in FWUpdate mode.
    Performing Mass Erase...
    <Never makes it past this point. No errors, just indefinite waiting>

    This is why I believe there might be some custom BSL code in the image of the EV2400. (Just a guess).

    I am open to other thoughts, but I understand if my options are limited due to not using the proper hardware. If this path does not work, I will probably just wire up the bq40z50 to a RPi and use some libraries there to configure the device. But I would much rather use bqSTUDIO, it looks much nicer.  That is why I wondered if TI would release the firmware binaries/source.

    Thanks again for all your help with this.