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This is not a project to take on lightly. If you don't know exactly what you are doing, you can damge the battery and/or cause the battery to go into thermal runaway and explode or burn.
A Li battery charger needs a monitor circuit to ensure that the following is met:
-Reverse polarity protection
-Charge temperature--must not be charged when temperature is lower -than 0° C or above 45° C.
-Charge current must not be too high, typically below 0.7 C.
-Charge voltage--a permanent fuse opens if too much voltage is applied to the battery terminals
-Overcharge protection--stops charge when voltage per cell rises above 4.30 volts.
-A fuse opens if the battery is ever exposed to temperatures above 100° C.
If you are determined to try it yourself, there are a number of integrated solutions that are used in chargers. Take a look for application notes that will give you some suggestions. Datasheets for one manufacturer are at:
I agree with House_Cat. I just would like to say that every Li-Ion battery for mobile phone already has internal protection for overcharge, overdischarge, loading overcurrent and shortcurrent. But anyway another protection from charger side doesn't hurt.
Hello.
A Li-ion battery charger is nothing else but a plain DC power supply. Inside the battery pack resides all the control, regulation and protection circuitry.
That is why to charge a cell telephone from an automobile 12V only a cable is used.
A Li-ion cell charger is a regulated 4,1000 V or 4,2000 V [depending on the cell chemistry and brand] supply.
The positive terminal of the cell has a rupture type aluminium disc diafragm theat serves both as a overcurrent fuse and an overpressure vent.
In order to charge a Li-ion cell, just obey the critical maximum voltage with a high precision voltmeter.
You can transistorize the chargers if you want.
Miguel
Herewith attached one circuit given by my friend of his mobile charger for same cellphone purchased from open market. I think it must be chinese, Comments on this circuit required. [/img]
Not every battery pack for mobile phone includes charge overcurrent protection. Battery manufacturers only start to include this function into battery. Recommended current rate 0.6C. With this rate battery is not overheating during charge time. Overheating above 60 C can cause permanent loss of capacity. Charger operates in constant current mode and monitors battery voltage. When voltage reaches certain value -4.2 V charger changes it's mode to constant voltage and monitor current. Current will be gradually decreasing. When it will be lower than 0.1C you can stop charging.
If you are going for regulatory testing for your mobile phone, the test house will ask for your battery charge, for safety/emc testing.
Do pay attention to charger, get it from reliable source, with proper safety test done (CE mark). This thing can explode if it is a low cost design, with poorly engineered PCB design. You don't want to land yourselve into trouble after selling thousands of these "bombs" into the market 8) !
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Miguel