• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 454 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ20z65 Balancing Current Question

Tan Eik Khoon
Prodigy 20 points

Other Parts Discussed in Thread: BQ20Z65

Hello,

 

i am currently using the BQ20z65 IC for a battery pack. The pack is 4series 6parallel (total 24 cells) using 2600mAh LIB cells. Nominal voltage is 3.7x4 = 14.8V and the capacity is 2.6Ah x 6 = 15.6Ah.

I am currently hampered by the low balancing current which is in the range of 5 - 10mA. But there is a possible solution to overcome with an external FET (but using the internal FET to drive)

For a 15.6Ah pack, do you have a guide for the required balancing current? could it be in the range of 1-2A??

The charging time for this battery pack is designed to be about 5hours and the discharge current is maximum of 4-5A.

Thank you very much for your kind assistance.

Regards

 

 

  • 0
    TI__Genius 10265 points

    It looks like it is possible to do that much current. You will need to make sure you size the bypass resistors and FETs correctly. For that much current, you are going to need resistors in the 5W to 10W range. The FETs will need to be power FETs.

  • 0 in reply to Chase7071949597
    Prodigy 20 points

    Dear Sir/Mdm,

     

    thank you very much for your reply.

    optimally i do not wish to increase the balancing current to that much as this will involve more components to the board. However, my consideration is that the capacity is 15.6Ah, which is quite a large battery pack. and 5-6mA may be insufficient to balance this.

    Solution 1

    Balancing Capacity 6mA x 5hr charging = 30mAh

    Percentage of balacing capacity of pack capacity = 30mAh/15600mAh * 100 = 0.19%

    This looks to be quite small

    Solution 2

    Balancing Capacity 500mA x 4hr charging = 2000mAh

    Percentage of balacing capacity of pack capacity = 4000mAh/15600mAh * 100 = 12.8%

    this looks more ok, but we are not sure if this is the norm or sufficient.

    As this is our first time using the BQ20z65, we are unsure really what to cater for the balancing current.

    Hope that you can help us to share some light.

     

    Thank you very much for your very kind advice.

  • 0 in reply to Tan Eik Khoon
    TI__Genius 10265 points

    The balancing algorithm in the z65 was designed to improve the lifetime of the cells, not the runtime. Fast balancing will help you improve runtime, but it will likely shorten the lifetime of the cells. It really depends on what you prefer in your end design. If your cells are well matched, you probably don't need more than a couple hundred mA of balancing current. 200mA balancing current will allow you to fix a 1000mAh imbalance in 5 hours. A 1000mAh imbalance is quite large and usually requires many cycles before appearing. Anything higher than 500mA is probably unnecessary, unless you have mismatched series cell capacities and they are constantly imbalanced.