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BQ34Z100-G1: Data Flash configuration for 12V - 42Ah Lead Acid battery

Hardik Panchal
Prodigy 62 points
Part Number: BQ34Z100-G1

Hi,

We are doing a learning cycle process for our fuel gauge BQ34Z100-G1. 

Our battery specifications are 

Name: Exide EP42 - 12

Voltage: 12V

Capacity: 42Ah 

We have figured out CHED-ID for our battery profile as 801.

In the attempt to learning the cycle for this fuel gauge and battery combination, we failed multiple times as our update status is not changing to 0x05. Before attempting a new learning cycle, we thought that we should reverify our data flash configurations. 

As mentioned in the application note of the learning cycle, for a successful learning cycle we need to configure Design Capacity, Design Energy, Quit Current, Taper Current, and Termination Voltage.

But as we go through multiple posts on the TI forum regarding the failure of the learning cycle we came to know that there are many such parameters that need to be configured and their values can lead to failure in the learning cycle. We don't have clarity about many parameters. 

The following parameters are discussed frequently in the TI forum and we are unsure as do we need to change these parameters for a successful learning cycle or go with the default value. Because these parameters are nowhere mentioned in the application note.

If someone can spread some light on the below parameters then it would be a big help.

1. Taper Current (After searching the forum we found that it should be between C/100 to C/10. For our case we have figured out it as (42000 / (ScaleFactor = 10)) / 20 = 210 mA )

2. Min Taper Current

3. Cell Taper Voltage

4. FC Set % (default is 100% but in some cases, they set it as -1. )

5. FC Clear %

6. SOC1 set/clear threshold

7. SOCF set/clear threshold

7. Load Select (default is 1 but how to select this value. Does this have any relation with learning cycle success ?)

8. Load Mode (0: constant current, 1: constant voltage)

We have gone through its description in this note: slua664 but it is still unclear that do we need to change this parameter or go with the default values to achieve a successful learning cycle.

Our design capacity is 42000 mAh which is scaled down to 4200 by a scale factor of 10. Same way design energy = 8400.

  • 0
    TI__Guru** 103155 points

    Hello Hardik,

    Have you followed the guide linked in this thread? https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/834847/bq34z100-g1-lead-acid-battery-configuration

    You shouldn't need to scale by 10, scaling by 2 should be fine. Have you reviewed the TRM for the information on those settings? www.ti.com/.../sluubw5

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 62 points

    Hi Wyatt,

    Thanks for looking into the issue. 

    - We had referred to the application note mentioned in the ticket for the lead-acid battery and also TRM. But still, we did not get clarification of the above parameters and that is why is choose to post the query here.

    Hereby I am rephrasing the Queries for you to understand well. Inline answers are appreciable. 

    1. Regarding the scaling factor of 10, if we use scale factor 2 then our design energy comes out to be ( 42000 (mAh) * (2V) / 2  = 42000 ). Which is out of range. Because of that, we have used a scaling factor of 10.

    2. In this SLUA925_bq34z100_G1.pdf, how the charge efficiency parameters will be used is given but we did not get an idea of what value should be set. We have kept  Charge Efficiency, Drop off,  reduction rate and, Temp compensation as default.

    3.FC Set % can be set -1 to 100. But in what conditions we should be set it to -1 and 100. Does this parameter affect the result of the learning cycle?

    4. We know that Load mode = 0 for constant current load but Load select can be (0 - 6). What value should we see? On which circumstance this parameter depends?

    5. Suggested charging rate in the app note is C/5 to C/2. In our case charging circuit limits us to a maximum charging current of 3.3 A which is < C/5. Can this lead to the failure of the learning cycle?

    6. As we have used scaling in our design capacity, does that mean we should consider that in all our calculations? For example, if we use a scale factor of 10 then while calculating the charging current of C/5, here Design Capacity (C) should be the actual one (42000 mAh) or the scaled one (4200 mAh)? Such clarification is not given in the datasheet or TRM.

    7. In the procedure of the lead-acid learning cycle, step 1 is charging the battery to full. What should be the state of the battery before proceeding? Should it be fully empty or any charge state can work?

    8. What is the indication of relaxing periods after charging and discharging? Is there any flag that we need to monitor or just strictly wait for a 2 and 5 hours timeline?

  • 0 in reply to Hardik Panchal
    Prodigy 62 points

    Hi Wyatt, 

    Any update on this, please?

  • +1 in reply to Hardik Panchal
    TI__Genius 10370 points

    Hardik,

    1) Scaling by 10 is not an issue. 

    2) These are battery specific and should come from the battery datasheet. Often default values are close.

    3) -1 Means only set the FC flag when Valid Charge Termination occurs. 100 means when SOC =100 set the FC flag. FC has no bearing on successful learning

    4) Load select determines which current is used to predict your remaining capacity. The recommended is #1 "Present Avg Dsg" which mean "how i am using it during this Dsg. There are others that can be more aggrerssive. Like Current means the current Sample which the simulation occurred on. If unknown i recommend 1

    5) Charge rate should not matter as long as you charge the battery to full. the DOD update is cirtical for learning

    6) You have to be above C/10 compared the the scaled design capacity (scaled). The C/5 is useful becuase you want a slow enough rate to allow you to discharge deep into the Voltage curve, but large enough to have a good IR drop for calculations. Again DOD is a good indication when you rest after the full Dsg your DOD should be 15.4k+

    7) Any state. 

    8) You can look for the DOD parameter to update or [VOK] to toggle.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 62 points

    Hi Eric,

    Thank you for the clarifications. Your answers are appreciable.

    I will try out a new learning cycle considering your suggestions and will update the status here.