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Original question:

BQ34Z100-G1: Gauge is reading 0% all of the time

BQ34Z100-G1: NiMH Battery Charges Up to 90% and Shuts Down at 33%

Eric Smith77
Intellectual 370 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100, GPCCHEM

I have coded up the fuel gauge IC with NiMH specifications and have it running off of a delta voltage method. However, the gauge reports about 90% when it is fully charged and reports about 33% before my device shuts off. Is there a setting that would be causing this? Does the gauge need more time to learn the cycle?

  • 0
    TI__Mastermind 42535 points

    Hi Eric,

    Please complete the learning cycle first. The gauge will then learn capacity and can then be used.

  • 0 in reply to Batt
    Intellectual 370 points

    The learning cycle for the NiMH battery states that I should discharge the cell until it is at least 100mV below terminate voltage. Is the terminate voltage referring to the minimum rated voltage on the battery data sheet or is it referring the minimum voltage of our application? For example, the rated voltage on the datasheet is 3V while our minimum voltage in the application has been set to 3.1V.

  • 0 in reply to Eric Smith77
    TI__Mastermind 42535 points

    Hi Eric,

    It refers to the minimum voltage of your application.

  • 0 in reply to Batt
    Intellectual 370 points

    I have run the learning cycles and it seems to have improved things. The battery charges to 100% now. However, the battery shuts down at 22%. The battery voltage looked correct throughout the discharge and the unit shut down at the voltage that we wanted it to. However, the gauge is returning 22% when it shuts down. I am running another charge and discharge cycle right now. Is there something else that I could do to improve this, or should I just continue learning cycles?

  • 0 in reply to Eric Smith77
    TI__Mastermind 42535 points

    Hi Eric,

    Please change your load select settings appropriately. NiMH has a large flat region that affects accuracy. You may need to change load select so that the simulations run at your actual rate of dsg when you are learning the battery.

  • 0 in reply to Batt
    Intellectual 370 points

    I initially had my load mode set to 0 (constant current mode) and my load select set to 3 (average current). I based this off of what the BQ34Z100 datasheet states for the recommended settings of NiMH batteries. I changed my load select to 1 (present average discharge current), which is what we had set for the Li-Ion solution that works well. I ran the learning cycle with those settings and then ran my unit under normal settings. The charge cycle worked well again, but the discharge cycle did not work. It shut down with unit stating that it was at 17%.

  • 0 in reply to Eric Smith77
    TI__Mastermind 42535 points

    Hi Eric,

    Please send your logs for analysis if you want us to look at it. NiMH can have errors due to chemistry match, you can expect a +/-10% error which can be higher under cases of changing temperature and other conditions.

  • 0 in reply to Batt
    Intellectual 370 points

    What logs would you like me to send?

  • 0 in reply to Eric Smith77
    TI__Mastermind 42535 points

    Hi Eric,

    Please send me your GPCCHEM logs and your learning cycle with registers exported every 1s and df exported every 1 min.

  • 0 in reply to Batt
    Intellectual 370 points

    I am in the process of gathering the logs for you. This product is being certified for ATEX certification. As a result, it is required that we put a 4.3Ω resistor in series on the battery voltage line. This causes a voltage drop across the resistor while we are charging/discharging the device. Our operation will typically discharge at 25 mA, which causes about a 100 mV drop across the resistor, which doesn't affect our application. However, the learning cycle states that we need to discharge the device at a C/5 to C/2 rating, which would be 200 mA to 500 mA for our battery. This causes a massive drop across the resistor, causing the gauge to read 2.2V when the battery is actually at 3.9V. I am thinking that this may be affecting our learning cycle. Would this affect our learning cycle? There is no way that we can remove that series resistor on our application. Is there a way that we can design our application for this?

  • 0 in reply to Eric Smith77
    TI__Mastermind 42535 points

    Hi Eric,

    Unfortunately no. The gauge needs to be able to read the battery voltage directly at all times. The problem is that any series resistance with the BAT pin will force the gauge to learn the battery resistance profile along with that pin. Therefore your OCV and all other values will be off.

  • 0 in reply to Batt
    Intellectual 370 points

    Attached are the GPCCHEM and learning cycle files. These are without any series resistance besides the PCB trace. We still cannot get it working without the series resistance.LarsonDavis_NiMHGPCCHEM.logLarsonDavis_NiMHLearningCycle.log

  • 0 in reply to Eric Smith77
    Intellectual 370 points

    With the GPCCHEM and the learning cycle files, the unit is still not working correctly. The unit shut off at 18% when it was at 3.37V. It should shut off at 3V.

  • 0 in reply to Eric Smith77
    Intellectual 370 points

    I found another bug with our setup. When I unplugged the charger, the gauge was still saying that the device was charging even though it wasn't. Our processor recognized that the charger was no longer plugged in. I feel like there is something deeper going on with our setup. Have you seen that bug before?

  • 0 in reply to Eric Smith77
    TI__Guru* 76230 points

    Eric,

    You will need to calibrate your units to make sure current voltage and temperature are being measured correctly. You will also need to verify your charge current threshold, discharge current threshold and quit current to ensure those are set correctly.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 370 points

    Thanks for all of your help. I figured out that issue. The way the our flash was set up to interact with the fuel gauge was incorrect. Now it is reading 0% correctly.