USING BQ78PL114

the parallel cells can be treated as one large cell for balancing purposes.  in a 3s4p configuration, you would only need two balancing circuits. 

you will need to place the temperature sencing circuit for the cells where you know it will give you the best data.  many designers place the sensor in the middle of the parrallel cell group.

we just released a new application note on cell balancing for the bq78PL114 that may help you.  you can find it from the product folder.

http://focus.ti.com/docs/prod/folders/print/bq78pl114.html

Thank you for your help,

1) Do you mean  that  the design we have shown for cell balancing is correct, am little bit confused on balancing, i have already gone through  the document on cell balancing, but i could not  find there, anything regarded parallel combination.

is there any new document? if yes, please send the link.

will given above cell balancing design work for 3s4p combination.  

2) another doubt is, which voltage v1, v2, v3 are going to show ,  means is V1  going to show the voltage of only cell 12 OR of the parallel combination of cell 9, 10, 11, 12. 

thanks and regards,

rohit

1) yes, your design is correct. 

2)  the voltages of the cells in parrallel will self balance.  cells 9, 10, 11, 12 will have the same voltage.  they will apear as one common voltage and combined capacitance.

i need to add that for cells to be considered parallel, you must connect the anodes and cathodes.  your schematic does not show this.

Do you mean the cell connection like this?

thanks and regards,

rohit.

yes.

BatteryBorne said:

you will need to place the temperature sencing circuit for the cells where you know it will give you the best data.  many designers place the sensor in the middle of the parrallel cell group.

What is considered the best data? What if a higher temperature variation is expected between cells (up to 5C?). Is it preferred to collect data for the warmest spot or the coldest spot?

The best place for the temperature sensors will depend on your system requirements. You may also want to check with your cell vendor to determine if the greatest risk to the cells is from high or low temperature in your implementation. The one temp sensor per cell capability of the bq78PL114 lets the device monitor the temperature of each cell group providing better temperature coverage than a single sensor.

thank u sir

i want to knw how actually cell balancing works, i read that document, but still i have doubts

1)suppose lower cell has voltage of 3.4v and upper has 3v.

then is lower cell going to charge upper cell and both will balance at 3.2v     OR     lower one stops  charging and and wait til upper comes to 3.4v

whats the operation

Sorry to bother you.I have some problems when I use bq78pl114EVM in voltage calibration.And I use 4-cells. According to User‘s Guide,I  calibrate voltage .I have updated the firmware to 5000 and began to calibrate voltage.

But the voltage reading is 4200mV ,and the actual voltage of Lithium battery is about 3800mV.There are differences between them ,I dont konw why.Bsides, I also use firmware 4452 to calibrate voltage ,and each of the voltage reading is about 3700mV,it is smaller than the actual voltage,and the error between them is too big(about 70mV each cells ) .So would you analysis the reason of this ?

Thanks