MediaEXL Brings U...: Li-Po charger and balancer

This is a Li-Po charger and balancer project for R/C hobby.The charger circuit is based on the circuit of Electron head and all folks in the DIY electronics topic on the rcgroups.com.

Detail

U1 do the fucntion constant current with limit curcent by R1 which calculated by

R1 = 1.25/Current in amps of current regulator.

for my project I need to charge 3 cell pack 620mAh.So R1 is

R1 = 1.25/.620 = 2.01612 Ohm

But I don't need to charge at 1C because I'm not sure the actual C rate(actualy may be 98-100% of battery specifications) .In my circuit I need to charge at 600mA or about 96% of 1C and R1 is 2.083 Ohm which formed by 3 X 1 Ohm in series and parallel with 100 Ohm 25 turns trimpot as the above circuit. Then adjust 100 Ohm trimpot to archive 600 mA (measure
by Amp meter at the output of U2)

U2 do the fucntion constant voltage,for 3 cell pack adjust R3 to get the voltage 12.6 v at the output .

Resistor R3(5K) in the balancer section I use 25 turns trimport and adjust to get the accross voltage for each cell is 4.2V (without cell connect).