Balancing two 14.8V batteries

Hi Morten,

Offhand, I don't think our existing products which incorporate cell balancing will work well in this situation.  Most of our parts will measure individual cells and calculate/control balancing, but here your "cells" are 14.8V each, which exceeds the cell-input ADC range of those parts.

One approach would be to insert a circuit between each battery and our existing device, to divide down the 14.8V by 4, then provide the divided-down voltage to the cell input on our device.  You can do this with a simple opamp circuit, connecting to the bq29209, which is a simple device that supports automatic cell balancing for two-cell applications.

You then need additional circuitry to reflect the balancing decision/control of the bq29209 back to the batteries.  This is getting complex, but I've sketched out a quick approach in the attached image based on this idea.  The 100-Ohm resistors are where the actual balancing current would flow, these can be sized to give you the level of balancing current you want to use.

A fallback approach is to digitize the battery voltages and develop your own balancing scheme in a uC, and have that control the balancing currents in the batteries.

Thanks,

Terry