BQ27426: Question about the effect of changes to the "Max Qmax Change" register?

A1: This depends on what you want to accomplish. It is possible to just change Max Qmax Change by itself. This parameter controls if the gauge qualifies the Qmax measurements for a Qmax update. See A2:

A2: This parameter controls, if the gauge qualifies a Qmax measurement. If the change in measured Qmax exceeds this value, the gauge will reject the update.

A3: The effect is that the gauge will reject Qmax measurements that exceed the changed value. If the real cell does have a significant change in Qmax, the gauging algorithm won't use the (correct) Qmax value if you configure the gauge to reject a correct Qmax value by narrowing this setting. This will impact every gauging result as Qmax is the basis for DOD, which is used by the algorithm to evaluate how the cell behaves.

A4: See A3: If you set this so that the gauge rejects valid Qmax measurements, FCC will become incorrect because the gauge evaluates the cell model incorrectly, if it has incorrect Qmax. The reason, why the gauge has many safe-guards for Qmax updates is due to the importance of accurate Qmax. You must make sure that you don't restrict the parameters for the rule set too much because that can have the effect that the gauge never learns Qmax. This will likely result in FCC that's too high (because Qmax shrinks over time and if the gauge doesn't update Qmax because you restrict the update too much with for example this parameter, the gauge will use Qmax that's too high to simulate FCC and that will be too high as well).

Hello Dominik，

Thanks for you reply。

Maybe I didn't describe the requirement clearly enough. Redescribe the requirements:

We want to use batteries with 55% battery aging, after multiple rounds of learning (passedcharge>Qmax*37%,satisfy the updating rules of Qmax and Ra), to confirm：The relationship between FCC and Qmax predicted by Fuelgauge for different aged batterie

Since there is a limit of ‘Max Qmax Change’ = 20% for Qmax update, I want to remove the limit and change it to ‘Max Qmax Change’ = 50%.

Q1：Do I need to change the ‘Qmax Max Delta %’, ‘Max % Default Qmax’ and ‘Qmax Filter’ registers besides ‘Max Qmax Change’ to 50%? What are the values to be modified? What is the basis?

Q2：To release the limit of Qmax, are there any other registers that need to be modified besides the above four registers? What values should be modified?

Q3：Do I need to modify ‘Ra Max Delta’ and ‘Ra Filter’? What values should be modified? What is the basis?

Q4：To release the limit of Ra, are there any other registers that need to be modified besides the above two registers?What values should be modified?

不同老化电池，Fuelgauge预测的FCC和测量的Qmax之间的对应关系

可能我描述的需求不够清晰。重新描述下需求：

我们想使用电池老化度55%的电池，经过多轮的学习(passedcharge>Qmax*37%,满足Qmax和Ra的更新规则)后，确认Fuelgauge预测的FCC和Qmax的关系。

因为Qmax更新有“Max Qmax Change”=20%的限制，所以想解除该限制，修改为“Max Qmax Change”=50%。

Q1：除了“Max Qmax Change”修改为50%以外，"Qmax Max Delta %"、"Max % Default Qmax"和"Qmax Filter"这三个寄存器是否需要修改？要修改成什么值？依据是什么？

Q2：关于Qmax的限制解除，除了上述四个寄存器以外，还有没有其它寄存器需要修改？要修改成什么值？

Q3："Ra Max Delta"和"Ra Filter"是否需要修改？要修改成什么值？依据是什么？

Q4：关于Ra的限制解除，除了上述2个寄存器以外，还有没有其它寄存器需要修改？要修改成什么值？

A1: You must change Max Qmax Change to allow for a 50% change (set to 50). Then you must change Qmax Max Delta % (set to 50) to increase the limit that the gauge applies after it qualifies the Qmax update. The last parameter, Max % Default Qmax is about how much above Design Capacity Qmax may grow so this doesn't apply to you use case.

A2: No.

A3: Not for Qmax updates.

A4: No.

Hello Dominik，

Thanks for you reply。

Q1、Does the ‘Qmax Filter’ parameter also not need to be changed?

Dominik Hartl11 said:

A1: You must change Max Qmax Change to allow for a 50% change (set to 50). Then you must change Qmax Max Delta % (set to 50) to increase the limit that the gauge applies after it qualifies the Qmax update. The last parameter, Max % Default Qmax is about how much above Design Capacity Qmax may grow so this doesn't apply to you use case.

Q2:Using a battery with 55% battery aging, RA may change significantly. Confirming the FCC and Qmax predicted by Fuelgauge, is it only necessary to change the Qmax limit and not to lift the Ra limit?

Dominik Hartl11 said:

A3: Not for Qmax updates.

A4: No.

Q1:"Qmax Filter"参数也不需要修改吗？

Q2:使用电池老化度55%的电池，RA变化应该会变大，确认Fuelgauge预测的FCC和Qmax，只更改Qmax的限制，不需要解除Ra的限制吗？

A1: This parameter is not related to the amount of Qmax change but to the minimum passed charge.

A2: There is no hard formula that correlates Qmax aging with Ra changes. You can change the Ra limits if you want to but it's not required (the Qmax limits are independent from the Ra limits)

Hello，Dominik，

Thanks for you reply。

1、If I want to modify the RA limit, what are the appropriate values for the ‘Ra Max Delta’ and ‘Ra Filter’ registers?

2. Besides the above two registers, what other registers should be modified at the same time? What is the appropriate value to modify?

1、如果要修改RA限制，"Ra Max Delta"和"Ra Filter"寄存器修改成什么值比较合适？

2、除了上述两个寄存器，还有哪些寄存器要同步修改？修改成什么值合适？