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Original question:

BQ34Z100-R2: BQStudio Battery voltage

BQ34Z100-R2: BQ34Z100EVM

PRABHAT RANJAN TRIPATHI
Expert 1102 points
Part Number: BQ34Z100-R2
Other Parts Discussed in Thread: BQ34Z100

I am using BQ34Z100 EVM, I have configured the gauge for correct cell configuration and was able to calibrate the voltage and current.

The EVM gives correct value of voltage when at rest but as soon as I connect a load the voltage value drops and the shown value does not matches with the multimeter reading.

Similarly as soon as I apply the charging current the voltage value rises and again mismatches with the multimeter reading.

I think this is due to the voltage drop or rise due to internal resistance of the battery, but this should happen at high current values however even when drawing 1 Amp current there is considerable drop in voltage.

How to get accurate voltage? If we don't get accurate voltage how will we be able to protect the cell from overvoltage and undervoltage conditions?

  • 0
    TI__Guru 57697 points

    Hello Prabhat,

    Check the voltage at the input to the bq34z100 IC and compare it to the voltage reading adjusted with the voltage divider.

  • 0 in reply to Shirish
    Expert 1102 points

    I have checked in the voltage at the terminal as well it shows the same as the BQ EVM. But my concern is it is not the cell voltage rather it is the terminal voltage.

    What I have observed is that if at no load a  4s battery has a voltage of 14.74V it changes to 15.75 V as soon as a charge current of 1.5 Amps is given, again if the same pack is subjected to a discharge current of 1Amps the terminal voltage drops to 14.44V. 

    How do TI solve this problem of getting accurate cell voltage?

    Because if terminal voltage is only measured then it will trigger false protection of over voltage and under voltage.

  • 0 in reply to PRABHAT RANJAN TRIPATHI
    TI__Guru 57697 points

    Hello Prabhat,

    The voltage of the battery will drop under load. Terminal voltage should be set to a value just above where the system will not work. Set the load mode and load select correctly. The algorithm will predict correct SOC based on the load settings. Once battery falls below terminal voltage, SOC will only come up after there is some charge current