• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 442 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.

BQ34110: I am having troubles determining correct time to empty with my current setup

Sahaj Saxena
Prodigy 20 points
Part Number: BQ34110

I am monitoring the charge and discharge cycles of a  lead acid battery using the bq34110 EVM board. I have attached the discharge characteristic curve of the battery used below. My battery is 12V,12Ah

    

Now as per this curve when I discharge at 7.2A (0.6CA), the battery should drain to 9.6V in 60 mins, So after the first charge and discharge the FCC is being updated to 7.2Ah, @ 7.2 A current which is fine, but when I do the next discharge at 3A (0.26CA), it gives out a incorrect time to empty as it considers the FCC to be 7.2Ah while the actual FCC will be around 9.2Ah. Thus from what I understand we would have to update the Voltage DOD levels and EVD thresholds every time we use a different discharge rate. 

My current application has a dynamic load so the discharge current can be anywhere from 1A to 10A. So is there a feature in the bq34110 IC that allows it to consider the change in discharge current and adjust the parameters like Remaining capacity, time to empty , full charge capacity etc.  

Currently I have configured the data memory corresponding to 7.2A discharge current. I have attached the gg file below for your reference 

 Batt1_7.2ADischarge.gg.csv

  • 0
    TI__Guru** 105590 points

    Hello Sahaj,

    The gauge will need to update the FCC in order to better estimate the SOC with different terminate voltages and loads. The BQ34110 is a CEDV gauge, which relies heavily on coulomb counting. Just by changing the terminate voltage will not accurately update the SOC for the gauge. Most applications use a fixed EDV point, if you are trying to vary the EDV depending on the load this will increase the difficulty in gauging since the end point moves dynamically with the load, it would be very difficult to gauge the system.

    The EDV point will need to be constant, and for CEDV gauges it will require an FCC update in order to adjust to the new a load applied, if the load changes significantly on the next discharge it could lead to incorrect SOC.

    Impedance Track may work better for your application since it uses the Ra table and Qmax with a load specified by the Load Select settings, which can use the real time current, CEDV gauges cannot do this.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Guru** 105590 points

    Hello Sahaj,

    It was noted through email that this application is a rarely discharged application and has a shorter timeline. For these reasons the BQ34110 was chosen, which I agree with the selection given the additional information.

    My comments above still apply, CEDV gauges rely heavily on coulomb counting with only voltage corrections near the EDV, so if you plan to update the terminate voltage depending on the load, it will be very hard to mitigate risks of SOC jump near end of discharge.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 20 points

    Hello Wyatt,

    First of all thanks for your prompt reply, Now from what I understood from the reply is that the IC bq34110 is not meant for the applications where the discharge current is not constant and vary  a lot like 1A to 10A in my case. In my application the end of discharge voltage is to be kept as 10.7V irrespective of the rate of discharge , thus I need an accurate time to empty and the State of Charge.

    So what is conclude is that the IC BQ34110 is not meant for my application and as per you suggestions battery gauges based on impedance tracking can be use. Thus if you can just confirm if my conclusion is correct as per the discussion above will be really helpful.

     

    Thank You

  • 0 in reply to Sahaj Saxena
    TI__Guru** 105590 points

    Hello Sahaj,

    For each algorithm there are different benefits. The BQ34110 has features targeting EOS detection, from my understanding this is a battery backup unit which means it is rarely discharged. The EOS functionality for this gauge can help determine the SOH for the pack with very small amount of discharge, compared to the impedance track which requires there to be at least a 37% change in DOD between two relaxation periods to update Qmax and the Ra table, which is not ideal for backup units.

    Since CEDV is mostly coulomb counter, you may see some errors in the gauging when the load is switched by large amounts, since CEDV doesn't account for internal resistance, it just uses the compensated EDV points to adjust near the end of discharge.

    Sincerely,

    Wyatt Keller