Circuit which indicates the charging level of battery

Hi friends ,As the need for rechargeable devices are increasing it is necessary to maintain the life of electronic devices which runs with  battery.Life of any rechargeable device depends upon the usage of charging capacity it has.Overcharging leads to reduce the life of device.Now a days due to overcharging many of the devices are out of work field.So if we know proper charging level of battery at every instant of time,it would help us to know whether to charge the battery or to use it.My circuit provides this features i.e when the battery is fully charged we can see a LED light glowing by this one will come to know that the battery is fully charged and has to unplug it.If not it need to be charged. Today i wanna show a circuit which will indicates the charging level of a DC storage battery.

Circuit description:

Input is an alternating voltage signal of 220v and 50hz supply,given to capacitor which is used to block DC,Stepdown transformer to reduce the signal level ,a rectifier to convert AC to DC,inverting and non inverting amplifiers,LED,1 v DC source and the battery whose charging level is to be detected.

Working:

Initially AC signal is passed through 'C' to block DC,which is fed to step down transformer to reduce the voltage signal from 220v to 13v.Now this is given to rectifier circuit for conversion process i.e from AC to DC.This constant 13V is given to non inverting terminal of opamp-1,inverting terminal is given with battery positive terminal for same opamp.Output of opamp-1 is given to inverting terminal of opamp-2 and its non inverting terminal is grounded.Output of opamp-2 is fed to LED which has -1v supply.

Operation:

case:1 Assume initially the battery has 2v in it ,V+>V-,therefore V01 is 13-2=11v,V02=-11v,since the potential at anode is much less than potential at cathode the LED doesnot glow.It means that battery is not yet fully charged.

case:2 Assume now the battery is fully charged i.e upto 13v,V+=V-,therefore V01=0,V02=0 and now the potential at anode(0v) is greater than potential at cathode(-1v),LED glows and indicates us that battery is fully charged and need to be unplugged.

*Since the ouput of rectifer is given to battery,it charges the battery when it is discharged by the user.

*Here two opamp are used,but the same work can be done with single opamp.For better explanation i has shown two.

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