Li-Ion Battery management (multi cell)

Amish,

If you need to gauge 24 LiFePO4 cells, then the bq34z100 will be the best choice that we have to offer. You will use an external resistor divider to scale the stack voltage to stay within the voltage range of the BAT pin. Since the devices' Voltage register is limited to 65V, we will need to scale the stack voltage when we calibrate the device.

Regards

Tom

Tom,

I think I can use the bq34z100 with the evaluation module, but I believe that the module is only able to handle 16 cells at a time. Would it be possible to stack two of these together to manage 24/32 cells together? 

I believe that using it in such a way would also make it such that the stack voltage across one device doesn't exceed 48V.

Another thing...can this module be configured to operate with a PIC series micro-controller to display the Soc?

Thanks

Amish

You will not be able to stack EVMs, but you can change the resistor divider ladder to support a higher battery stack voltage. You can use the Voltage Divider equation on page 26 of the datasheet to calculate new resistor values and then change one of the 300 kohm resistors on the EVM. If you are using 24 LiFePO4 cells, then the stack voltage will be equal to 24 * 3.6 = 86.4V. This exceeds 65V, so you will need to scale the voltage by divide-by-2. You will set the number of series cells to 12. You will measure the stack voltage during calibraton and divide it by 2 and enter this value when calibrating the voltage. The reported voltage will then be divided by 2 and you rescale it in your uC.

You can communicate with the device over the I2C interface to read parameters, including SOC.

Best regards
Tom

Tom,

So, I just need to recalculate the resistor values to scale the voltage applied?

Another thing, won't I be connecting the cells to the module individually? If so, wouldn't the number of pins on the board be insufficient?

And correct me if I'm wrong, but this module cannot balance the cells, can it?

Sorry if some of my questions are basic, but I am a student working on a project.

Thanks,

Amish

Amish, 

Yes, you will need to set the resistor values to scale the full scale voltage to be less than 0.9V at the Bat in on the device. The bq34z100 will only measure the stack voltage and it does not monitor or balance the individual cells in the stack.

Regards
Tom

Tom,

What if I was to use the bq76pl536 chip?

Can I buy EVM's and stack them together?

And is it able to perform balancing internally? Or does it require external circuitry?

Thanks

Amish,

I do not support the PL536, but another applications engineer will address your questions.

Tom