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BQ34Z100-G1: BQ34Z100EVM can't calibrate to zero current with electronic load device connected

Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100EVM, BQSTUDIO

Hello,

My BQ34Z100EVM set-up has both a charger and  CBA (electronic load device) connected in preparation for learning.
The issue arises with the CBA connected, yet the current measured between the EVM and the CBA is zero.

With no current flow,  the gauge reads 22mA after an automatic Board Offset calibration in BQSTUDIO.
Forcing Board Offset=-128 (max value) reduces it to 14mA.

I used the following master reboot procedure to get to this point.

(1) Computer reboot, reinstall newest version of BQSTUDIO
(2) Disconnect EVM (Unplug EVM connections to EV2300 I2C, Battery, Charger & CBA)
(3) Reconnect EVM
(4) Program the newest firmware
(5) Import the DataFlash from GG file created for learning.
(6) Calibrate CC offset, Board Offset, and then Voltage.

I didn't have this issue for the ChemID data log run because I calibrated the EVM without the charger and CBA connected.
The charger was connected only for the charge phase, and the CBA was connected only for the discharge phase.

For learning, is it problematic to connect the electronic load device only during the discharge phases?

If so, can I resolve the non-zero current issue?

Sincerely,

Rom Caroselli

  • Hello Rom,

    It sounds like your e-load may not be high impedance, you should do calibration with no load currents and no devices attached if possible. It's common for equipment to draw some small current if they are not set to high-Z modes. The standby current should be as low as possible for learning co the gauge gets accurate OCV measurements. I would disconnect the E-load if possible during the no load rest periods.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    Okay, I'll do that.
    Thank You.


    Sincerely,

    Rom

  • Hello Wyatt,

    The current error on discharge is not acceptable.

    When the eload is discharging 7000mA, the gauge is reading 60mA low.
     I've calibrated the current with 2X scaling, so the current error for gauging is 2X, or 120mA.

    I suspect the issue is grounding related because

    (1) The current offset is affected by changing USB cords to the eload.
    (2) The zero offset error remains when the positive connector to the eload is unplugged. The current zeros only when the negative connector is unplugged.

    Also, I2C comm errors appear to be more prevalent when the eload is connected.

    I couldn't find any threads pertaining to grounding issues.
    I don't know what else to try other than using a passive load.

    Is a constant current discharge important for learning?
    I have power resistor I could use.

    Please advise.

    Sincerely,

    Rom

  • Hello Rom,

    Some Eloads can cause issues due to they feedback control systems as well. It could also be related to the ground scheme of the Eload.

    It is important to have a CC discharge for the best Ra table updates in the golden image used for programming.

    Sincerely,

    Wyatt Keller