internal box charger

[ouada]

i have an old njoy usb charger laying around. Is it possible to put it in a box, and use it to charge a 3.7 volt 900 mah battery?

 

[Budjiman1]

I wish someone would post the answer and a how to...I'd love to know how to do this also!

 

[rannox]

Its possible. If its the same as most usb chargers it has a little 200 mah charging circuit board in it. Basically take it out, connect up the positive and negative, good to go.

But you need to make sure it doesnt overcharge, some rely on the battery protection circuit, which is a no go, things can go boom.

There are tutorials and questions for usb charging all around the forum, search for em.

 

[Java_Az]

It for sure can be used to charge a single battery. But the bad thing about using the ecig chargers is the ones i have taken apart dont have any reverse blocking. When not charging they will be eating at least 10ma at all times. If you hook one to a fully charged battery 4.2 volts it will light up the led indicator. It might not sound like much but it does add up over time. Some of the better charging IC's have a reverse current drain of .05 to 1.0 uA . To give you an idea it takes 1000 ma to = 1 amp it takes 1,000,000 uA to = 1 amp.

To use one of the ecig chargers is straight forward you take the positive from the charger to the positive of the battery. negitive to the negitive of the battery or any ground close by. USB doesnt change. Thats about all there is to it. A switch could be added to the positive going to the battery so it can be turned off to eliminate the reverse current drain, Thats what i would do anyways.

 

[utak3r]

True, chargers inside these cheap "universal chargers" after disconnecting the external power will drain the cell! So you would have to make a switch to disconnect them.