How to hook up LED to indicate battery is receiving current

[John1397]

I want to charge up a 12 volt car battery with an AC voltage passing thru a full wave bridge diode and I want my LED to be on when current is being supplied to the battery terminal and if circuit stops producing current for any reason LED will be off and not on as if it where receiving current from the battery how would one wire this as I am thinking a diode at battery terminal to allow current to pass, but not return?

John

 

[mheslep]

Easiest method is probably an inductive pickup. Try this:
http://www.hcs77.com/current_indicator_cr2530.htm

Otherwise you need a very low resistance, high power resistor in line with a transistor across the R.

 

[vk6kro]

I want to charge up a 12 volt car battery with an AC voltage passing thru a full wave bridge diode and I want my LED to be on when current is being supplied to the battery terminal and if circuit stops producing current for any reason LED will be off and not on as if it where receiving current from the battery how would one wire this as I am thinking a diode at battery terminal to allow current to pass, but not return?

John

The best way would be to just put a meter in the circuit. This would tell you how much current is flowing.

You can get 4 digit digital ammeters on Internet (Ebay "buy it now") that can be mounted anywhere on the panel of a battery charger.

If you wanted an indication of full charge, you could use a reed switch and wrap some turns of wire around it to make it switch with current like this:

http://dl.dropbox.com/u/4222062/reed%20switch.PNG

"LOAD", in this case, is the battery.

The wire would have to carry the full current of the battery charger, so it would have to be thick enough to do this. You might need about 50 turns of wire around the glass bulb of the reed switch.

Another way is to use a 12 volt 2 amp tail light bulb. Just put this in series with the output of the battery charger. With this, you can even short out the leads and the lamp will just light up without doing any damage.
The lamp will be bright on a flat battery and gradually dim as the battery charges up.