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BQ34Z100: SOH Update Clarifications

Pier-Luc Côté
Prodigy 10 points
Part Number: BQ34Z100

Hi, I'd need some clarification about the SOH update available on the BQ34Z100 on a lead-acid battery.

 

This post [https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/993404/bq34z100-maintenance-cycle-to-update-soh/3669498] seems to tell that we need to discharge the lead-acid battery of 37% to update the SOH.

 

However this other post [

https://e2e.ti.com/support/power-management/f/power-management-forum/714383/bq34z100-g1-minimum-requirements-for-soh-update] seems to tell that the SOH is not linked to the SoC, but to the FCC Update.

 

Question 1 : What information is the right one? In other words, can I get (precise value or not) a SOH estimate if my battery oscillates only between 100% SoC and and 80% SoC in normal operation ? What about less than that ?  

 

Also, in the slua450 it is written that "In order to ensure high accuracy of the DOD measurement, the Qmax calculation does not occur if the temperature is above 40 or below 10. Il also does not occur if at least one of voltage measurement for DOD1 or DOD2 was taken in the cell voltage range between 3737 mV and 3800mV because of very flat OCV(DOD) dependence in this range." and then that "These limits are chemistry dependant and are specified for different chemistries separately" and then that "Qmax is calculated as Qmax = PassedCharge / (DOD2-DOD1)".

 

Question 2 : Considering this, can I know these limits for my lead-acid battery chemistry? It is certainly different from the one specified in the slua450 since the OCV curve of a lead-acid battery is definitely different from a lithium-ion battery and their performances in temperature is also different. 

Thank you 

  • 0
    TI__Genius 10370 points

    Pier-Luc,

    1) SOH is calculated from QMAX and the Ra table. It is always being updated since these values are learned. It will be recalculated every time the gauge does a simulation, but if QMax and Ra are not updated you will not get a new value. So high level both posts are right. 1) You need the 37% to get a qmax update which impacts SOH accuracy. SOH is re-computed the same time FCC is.

    2) The "Flat zone" is unique for each chemID. Please let me know the ID you are using and i can let you know your range. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 20 points

    Hello Eric, I am Pier-Luc's colleague. 
    The chemID we are using is 808. In our application, the SOC will always be between 95% and 80%. Can we still use the BQ34Z100 to estimate the SOH ? In our case, it would be acceptable to have a certain degradation of the SOH (10-15% of error).

  • 0 in reply to Vincent Richard
    TI__Genius 10370 points

    Vincent,

    ID 808 is a lead acid. Unfortunately only doing a 10% discharge will not give the gauge enough discharge to effectively keep track of the internal impedance (Ra) of the cell nor the unloaded Capacity (Qmax). I do not think the bq34z100 will work for this type of use case, or rather TI can not guarentee any sort of SOH accuracy. 

    To get good results for SOH a full discharge is needed periodically to allow for resistance updates to occur.

    Thanks,

    Eric Vos