How would I begin to make a charger for a 7.4V 900mAh 15C Lithium Polymer Battery from a wall source and/or solar panels?
Life Is Like A Bucket Of Chicken.
I would begin looking for specific IC's for this exact application, and forget to do it in any other way. And also, try to charge both cells separately.
If this is for recycled units, the I would forget at all. They ARE DANGEROUS.
"Common sense is the least common of the senses" Anonymous.
First google for battery charging methods. You will find the theorytical way of Lithium Polymer batteries charging method. Then the way of doing this depends on you. As Guillem said there are ics doing this for you (take a look at maxim).
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As Guillem stated, you NEED a charge controller IC, as well as some additional protection for some of them. I would recommend contacting your battery's manufacturer and use their preferred charge circuit as is.
Li-Ion and Li-Poly batteries have a nasty tendency to explode rather violently if overcharged or mistreated...
This is a cheap unit I don't have much info on it except this:
Dimensions: 2.13 in x 1.18 in x 0.59 in
Weight: 1.76 oz
Type: Lithium Polymer
Blue Line (In the middle) is my battery.
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Do charging IC have voltage and amperage control(beside there regular function)? I don't know much about charging IC, is there a place that explains them(or a specific one), also could someone give me and example IC that I would use?
Charge controller IC's are made specifically for one type of battery, they limit how much a battery will be charged OR discharge, so it doesn't explode. To select an IC you will first of all need to know how many cells in the battery, the voltage, the rated discharge point, etc etc... If you do not know the battery pack details, it is safer to dispose of it and get a new one. At the same time ask the manufacturer what is their preferred charge controller circuit for this model.
I cannot stress this more, if you discharge the battery too much, it WILL get damaged, and you run the risk of leaks and/or explosion. If you charge it too much, same.
Just think of it this way, Apple recently had to recall a whole bunch of iPod nanos because even they couldn't get the battery circuit right and some exploded or catched fire during usage.
Protection and charging are two seperate things. Usually battery packs have a little IC in them that cut the connection to the outside world if the battery is dangerously close to being undercharged or overcharged, or becomes too hot.
The charger is seperate, but needs to know the chemistry and number of cells and current rating.
Linear Technology has a whole range of charger ICs here
Some only need a singe resistor to work, but (unfortunately) most come in tiny SMT packages.
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