WWW.EEE-LAB.COM

We can charge a battery in many ways but constant current charging system is that which, in particular, is  a popular system for lead acid and Ni-Cd batteries.In this circuit, the battery is charged with a constant current that is  generally  one-tenth  of  the  battery capacity  in  ampere-hours.  So  for  a 4.5Ah battery,  constant  charging  current would be 450 mA.

Advantage of this charger :
1. It can charge 6V, 9V and 12V batteries. Batteries rated at other voltages can be charged by changing the values of zener diodes ZD1 and ZD2.
2.  Constant  current  can  be  set  as per  the  battery  capacity  by  using  a potmeter and multimeter in series with the battery.
3. Once the battery is fully charged, it will attain certain voltage level (e.g. 13.5-14.2V in the case of a 12V battery),  give  indication  and  the  charger  will  switch off automatically. You need not  remove the battery from the circuit.
4.  If  the  battery  is  discharged  below a limit, it will give deep-discharge indication.
5. Quiescent  current  is  less  than 5  mA and mostly due to zeners.
6. DC  source voltage ranges  from 9V to 24V.
7. Short circuit protected.

Read more about this circuit. just click : 1. 2.