• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 693 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Looking for help in choosing a Fuel gauge for robotics application

mike martone
Prodigy 40 points
Other Parts Discussed in Thread: BQ40Z50, BQ3060, BQ34Z100

I am new to battery management and I have been reading a great deal of information causing information overload and confusion. I am working with a 4S3P lithium Battery pack with an external charger and looking to add a Fuel Gauge. We intend on using batteries from different manufacturers, and do not "think" we need battery balancing functionality.

I tried the TI Fuel Gauge selection page at:

http://www.ti.com/lsds/ti/power-management/battery-fuel-gauge-products.page 

But I am not sure if I am doing something wrong, and there are some terms in the selection processes that i need some clarification in what they are asking. This is what I have:

  • STATUS:  ACTIVE  -   Active is the only choice but not sure what they are looking for here...
  • NUMBER SERIES CELLS:   This the number of cells in series or the total number of cells. My application has 4S3P  or 4 cells in series so I selected:  2-4 CELLS
  • CELL CHEMISTRY:   Li-ion  
  • COMMUNICATIONS INTERFACE:  I2C or SMBus
  • BATTERY CAPACITY (min/max): is this the pack or individual cell capacity?  Each cell has a capacity of 2500 to 2600 mAh, the pack has a total of  7500 to 7800mAh.
  • IMPLEMENTATION (PACK/SYSTEM):  is this where the fuel gauge circuity resides? Fuel Gauge circuitry is in the battery pack or mounted externally on the system.  We would like to have ours mounted outside of the pack itself.  However when I enter the number of cells in series there are SYSTEM implementations shown.  It appears that I can only us a fuel gauge that is on the pack itself when there are greater than one cells used. Is that correct?
  • EXTERNAL CAPACITY INDICATION:  None, since we can read it through the I2C/SMBus
  • GAS GAUGE ALGORITHM:  I believe we need to use impedance tracking since we want it to adjust to different batteries from different manufacturers?

i would greatly appreciate any feedback from the experts out there...

Thanks in advance - mike

  • 0
    Prodigy 40 points

    It appears that if you are doing fuel gauging with more than a single battery (in series) your fuel gauge IC must be on the pack itself?  Are there any alternative way to perform fuel gauging on a 4s3P pack without having it on the pack itself?

    Thanks - mike

  • 0
    TI__Expert 6470 points

    Hi Mike,

    The active (recommended) devices for a 4S3P application are bq40z50 (Impedance Track) and bq3060 (CEDV). Impedance track is more accurate, while CEDV is quite a bit easier to grasp the concept and debug. Your capacity is in line with the design parameters for those two gauges.

    There is a third alternative, the bq34z100 which could be better for your "pack side" application if you cannot access all the nodes in the battery stack. However, you would still need protection and balancing for each cell block since the bq34z100 is just a gauge.

    "pack side" gauging is possible, but there are some things to consider. First, if there is the option to swap out a battery in a system, you have to make sure that the new one has exactly the same chemistry. Both Z-Track and CEDV are extremely sensitive to the particular Li-Ion chemistry formula. Using different batteries from different manufacturers is generally only possible when you have separate optimized projects, one for each cell type.

    Theoretically, you could work around that problem by identifying cells from different manufacturers that use the same formula. Or, you could have a method to reprogram the chemical database coincident with changing the battery in your system.

    Regards,

    Doug

  • 0 in reply to Doug Williams4811
    Prodigy 40 points

    Hi Doug,

    Thank you for your help. I am confused with the terminaology, when you refer to a "pack side" application do you mean the feul gauge should be in the pack itself?  We are trying to keep the feul gauge outside of the pack.

    Other information:

    1) The user will be able to swap out the battery pack.

    2) We will most likely have different manufacturers supllying the pack.

    Thanks again for your insight and help. I appreciate it immensly! - mike