Please somebody help me. I wanted to have an LED to indicate that my battery is being charged. I tried first by placing the LED on the Input side and then on the output side (with a 1K series resistor, so that less current flows through the LED) of the LM317. Both the times this resulted in less current at the output.

Now my question is how to have an LED showing that the battery is being charged without reducing the output current for the battery.

 

I am using a 12v 7ah battery. The output of LM317 is set at 14.2v and current limit set to 400mA. The LED i'm using has a voltage drop of 2.5v and the current rating is 30mA. Though there is voltage drop at the output when LED is used, as i mentioned before, use of LED reduces the output current. Please somebody help me out.

 

Schematic, schematic, schematic.............

 

Do you want to detect when current is flowing to the battery or just that there's voltage available?

Post a schematic.

 

Sometimes it just requires work.

 

I am using a 12v 7ah battery. The output of LM317 is set at 14.2v and current limit set to 400mA. The LED i'm using has a voltage drop of 2.5v and the current rating is 30mA. Though there is voltage drop at the output when LED is used, as i mentioned before, use of LED reduces the output current. Please somebody help me out.

You have to use a comparator to light the LED when the charging current drops to about .03C with the battery voltage at about 13.6V.

Here is a design I did for a temperature compensated battery charger for lead acid battery with end of charge detect.

 

Hi #12,

I tried your method. The current at the output didn't decrease. Thanks you saved my day.

 

Thank you everyone for your replies

 

Bountyhunter's circuit is also valid. Which one you choose depends on how accurate you need to be...and how good you are at assembling something with a couple of dozen parts in it.

and whether you have enough extra voltage available to drive the current indicator in my circuit.

 

If you put a current sense resistor in the ground wire (after the battery) then it won't affect the voltage regulation and can be used as a 0.6v sense signal to turn on a NPN, which can then light the LED.

That only requires a headroom of 0.6v compared to >2v or so to operate a LED and its series resistor.