Inquiry Regarding Cell Balancing Features in MC33772 with S32K144

[sonthaikhac308]

Dear NXP Support Team,

I am currently using the MC33772 and S32K144 for battery management in my project. However, I am not fully clear about the cell balancing functionality. I have noticed that there are two modes of cell balancing: global balancing and individual cell balancing, with specific time settings for each mode.

I have the following questions:

1. In the individual cell balancing mode, how is the time required to complete the balancing determined?
2. What are the potential issues if the balancing time is set too short or too long in individual cell balancing mode?

Understanding these aspects is crucial for optimizing the performance and reliability of the battery management system. I would appreciate any detailed information or guidance you can provide on this topic.

Thank you for your assistance.

Best regards,

[JozefKozon]

Dear Sonthaikhac,

this is very well described in the sections 6.3 Recommendations for SYS_CFG1 and SYS_CFG2 registers and 8 Cell balancing in an AN12084 MC33771B/MC33772B programming guide. 

Please download the AN12084 from the MC33772C product page, under the secure files.

Please also refer to the AN12637.

With Best Regards,

Jozef

[sonthaikhac308]

Hello @JozefKozon ,

Thank you for your continued support. I have a few questions related to the Cell Balancing functionality in the BMS system using MC33772:

1. Cell Balancing Time Formula:

   I am using the following formula to calculate the cell balancing time:

   Balancing time = (ΔV * C_rate) / I_bal​​

   Where:

   • ΔV: maximum voltage deviation between cells
   • C_rate: nominal capacity of the battery (Ah)
   • I_bal: balancing current (A)

   Could you please confirm if this formula is correct? If not, could you provide the accurate formula?

2. Actual Balancing Time:

   When applying the formula above with practical values (for example: ΔV = 50mV, C_rate = 32Ah, I_bal = 0.1A), the balancing time comes out to be 16 hours. This seems very long compared to the balancing time mentioned in the datasheet (ranging from 0.5ms to 511ms).

   I am concerned that if the balancing time is this long during an over-voltage situation, would it still ensure safety for the battery and the users? Please help clarify this issue.

3. Reading voltage and current during balancing:

   During the Cell Balancing process, is it possible to continue reading the voltage and current values of the battery? Some references suggest this might lead to inaccurate readings due to the influence of balancing current. Could you please confirm this?

I would greatly appreciate NXP’s support on the above questions.

Best regards,
Sonthaikhac