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BQ34Z100EVM: 3s 5000mah lipo battery fuel gauging with 30 Ampere discharge. Will it work?

Parthasarathi Venkatesan
Prodigy 20 points
Part Number: BQ34Z100EVM
Other Parts Discussed in Thread: BQ40Z50-R1, , BQ34Z100-G1

Hi all,

Im a newbie to the power management world.!

I'm currently working on a project that requires a 5000mah 20-30 C 11.1 v 3s lipo battery to be charged and discharged simultaneously. 

My load is a motor which draws a continuous current of 20 A & i need a fuel gauge to find the SOC of my battery.

I thought i could get a 30 A 3s BMS and wire the fuel gauge onto it. How ever after going through various TI bq series data sheets i'm all the more confused. 

I dont get it. The datasheet says the maximum charge & discharge current is 7 Amps while my load draws about 20 Amps. 

Is there any way to find the SOC of my battery with a 20 amp discharge. Please do suggest me with some ideas. 

Thank You..!! 

  • 0
    TI__Mastermind 34745 points
    Hi Parthasarathi ,

    Can you reference where you read about the 7A limitation? Our Multi-cell gauges can support up to 32A. You can also use current scaling for >32A. Do you have access to your individual cells in you 3S battery pack? If so I would also recommend bq40z50-R1 for your application.
  • 0 in reply to Damian Lewis
    TI__Intellectual 1840 points

    Damian/Parthasarathi

    The EVM's datasheet which sets the maximum pulse current to 7A, with 2A continuous. But this is most likely due to the EVM's PCB's trace current rating, connectors/sockets current rating, and the sense resistor's power rating (which is 1/2W at 0.01 ohms and can only handle pulse/peak current of 7A).

  • 0 in reply to Damian Lewis
    Prodigy 20 points

    sluu904a.pdf

    This is the data sheet which i referred to.....im using a 3s 5000mah battery which i got from hobby king . i dont think i have access to individual cells . (correct me if im wrong). 

    Im surprised to know that the gauges can support high currents. Im not sure if u r referring to the IC alone or an evaluation board with it also. 

    Please refer me to the product if so. 

    Thank you for your reply!!  :)) 

  • 0 in reply to Parthasarathi Venkatesan
    TI__Mastermind 34745 points
    Hi Parthasarathi,

    Since you don't have access to the 3 individual cells in the battery pack, bq34z100-G1 would best for your application. Device can handle large currents > 7A. The limitation is the bq34z100EVM was designed to support a max current of 7A. Here's some info on bq34z100-G1 High Cell Count and High Capacity Applications.

    www.ti.com/.../slua760

    For your application you will need to change Rsense value (R30) < 3-mohm. Current value of R30 is 10.75-mohm, which would violate the V(SR) max value of +/-0.125V.

    6.10 Electrical Characteristics: Integrating ADC (Coulomb Counter) Characteristics on page 6 of the datasheet.

    www.ti.com/.../bq34z100-g1.pdf