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BQ27441-G1: The consequences of using a battery with different Chem ID

Abdulmalik Almazrua
Prodigy 10 points
Part Number: BQ27441-G1
Other Parts Discussed in Thread: BQ25606

we are using bq27441 in our products. we are planning to use a new li-ion battery with a protection circuit attached to it. We are aware that the chem Id cannot be changed and it’s 128.
However when we acquired V, I and T values and send the results to gpc, we found that Dod is 35% and therefore not suitable.

We have questions regarding the test we did and its results:
1- does the protection circuit attached to it affect the results? Should we do the test without the protection circuit? for me I believe we should do the test with the protection since we are going to use it but I need your confirmation in this point.

2- if we go forward and do the learning cycle, what are the consequences of using high Dod error? the battery in the product will be connected all the time. I understand that when the battery is reconnected, it will not give the accurate soc, but if we charge and discharge the product, the gauge will be soc with good enough accuracy? or other issues will be apparent later? Like soc jumps or anything else?

3- does the charging speed affect the gpc results? or it’s not relevant.

4- we are interested in using in the future TI GDK kit to acquire the data for gpc. Can we still use it as well to acquire the learning cycle after programming the gauge with chem Id 128 and the charger charging current with what we use in our product? Is this a good idea or we should use just for gpc and use bq27441 and the same charger we use in our products?

Thank you for assistance. We need to take the decision to use the new battery or not.

  • +1
    TI__Mastermind 27321 points

    Hello,

    1- Overall protections do not affect unless they get triggered. If protections trigger most likely you will not be able to charge or discharge the cells. If you do not the thresholds at which protections will trigger, then it is fine for your test.

    2- A max DOD error of 3% is allowed to proceed with the learning cycle. The gauge relies on the ChemID to predict SOC, SOH, FCC, RM, etc.

    3- Do you mean charging rate? It is recommended to charge with a rate of C/2 or lower. 

    4- GDK is no longer supported. Please refer to this E2E thread.

    Regards,
    Jose Couso

  • 0
    Prodigy 10 points

    Hello Jose, 

    Thank you for your response. it makes sense now. I have questions regarding the learning cycle: 

    1- Is it required to charge the battery in the learning cycle with a current rate equal to the one we use in our product?

    2- we are aware that the learning cycle is needed for Qmax and Ra values, does preforming the learning cycle on different environments (different charger types, or different gauges but using the same Chem ID) generate similar results? can we do our learning cycle on bq27441EVM connected to bq25606EVM and use the golden images on all our products that use the same battery and bq27441? 

    3- Currently, we are planning to upgrade from bq27441 to flash-based gauge. The reason is that we need a gauge with external temperature support Ts, and make us able to have more selections of battery by letting us program Chem ID. 

    Thank you for your support. I appreciate your effort. 

    Best regards,

    Malik

  • 0 in reply to Abdulmalik Almazrua
    TI__Mastermind 27321 points

    Hello Malik,

    1- We recommend to charge with a rate of C/2

    2- Learning cycle procedure should only be done in one gauge. You can use the BQ27441 EVM to do this. Once the learning cycle is done, please run your system load profile and test it in your application. Do a few charge and discharge cycles and ensure the gauge is working as expected. Extra tuning might be needing. TI will be able to help you with the tuning process.

    3- BQ27z561 should be a good match. This is PACK side implementation.

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    Prodigy 10 points

    Hello Jose, 

    thank you for your answers. 

    Setting the charge with a rate of C/2 in the learning cycle does not make sense to me. we use BQ25606 and its cutoff current is 5% of its charge rate. The tamper current is set in the gauge based on this value right? 

    Lets say we have two identical products that use bq27441 as a gauge and bq25606 as a charger and they use the same battery type. the only difference is that product A has a charge rate of C/5 (therefore cutoff current of C/5 *5%) and product B has a charge rate of C  (therefore cutoff current of C *5%). 

    if we perform the learning cycle with a rate of C/2, we will have to define the taper current before the leaning cycle to be (C/2 *5%)*120%. This cannot be applicable in both product A and B right? 

    in this example the only solution is to do two different learning cycle for both A and B and use their charging rates in the learning cycle right?

    What I understand so far is that two different products with different charging rates can share the same learning cycle, but if they have different cutoff currents, they cannot share and two learning cycles are needed. could you elaborate on this point please and confirm if it is right? 

    Best regards,

    Malik

  • 0 in reply to Abdulmalik Almazrua
    TI__Mastermind 27321 points

    Hi Malik,

    The C/2 is a recommended value. You can charge at rates lower than C/2. C/5 should not be a problem, it just takes 5 hours to reach charging voltage. 
    Same for taper current, often recommended C/20, but it could be any value from C/10 and C/100. See below for better description.



    One hint is to set the taper current in the gauge 10% higher than the charger taper. This is to ensure the gauge detects full charge before the charger does.

    Regards,
    Jose Couso