charging li-ion batteries...

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What should the range of the output voltage if I am charging a 3.7 li-ion for handphone....
 

messlia said:
What should the range of the output voltage if I am charging a 3.7 li-ion for handphone....
Click to expand...

Hi Messlia and welcome to EDABoard,

You mean cell phone with "handphone" ?

At least charger will need voltage 4,5-5V. For example you can charge cell phone from USB port on PC.

Most Li-Ion batteries without charger can go to 2,7V low, and this is complete discharged state of battery. When battery is charging most of Li-Ion batteries goes to voltage of 4,2V. Nominal voltage is 3,7V.




Best regards,
Peter
 
What should the range of the output voltage if I am charging a 3.7 li-ion for handphone....
Click to expand...
Hi messlia
Out put voltage of what ? of your charger ? it can be some percent higher than the nominal voltage which has been rated on your battery . for instance 3.7 volt battery can be charged by 5 volt . do you know why ? because of preventing of your charger being load of the battery !

Best Wishes
Goldsmith
 
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    tpetar

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I will be using the voltage regulator 7805 to give out the 5V... do I need limit the output current to follow the current of the battery using a resistor connected to the output

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I am using a lm 7805 to charge the battery...
 

Do not do that!
Even with a resistor in series the battery could overheat and explode. There are many inexpensive ICs available that provide the proper V/I charging characteristics (Linear, Maxim, National etc.) E
 

messlia said:
I will be using the voltage regulator 7805 to give out the 5V... do I need limit the output current to follow the current of the battery using a resistor connected to the output


I am using a lm 7805 to charge the battery...
Click to expand...


You need charger circuit for Li-Ion battery.

Its dangerous just to hook 5V to battery. That can be done with cell phones, because charger is inside phone, but if you connect only battery to 5V that is dangerous.


Try to use small and simple MCP73832 Single Cell Li-Ion Li-Po Charger IC:





Some other simpler examples :

Simpe Li-Ion and Li-Pol cell charger with LM317
http://danyk.cz/li-ion_en.html






Build-in Li-ion accu charger TL431 - new version
http://www.belza.cz/charge/liich.htm





Best regards,
Peter
 

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hey,

It say the input voltage to the lm317 to be between 9 V to 12V.. I am to design a circuit based on variable input between 3 V to 12V ....is there was to increase the voltage up and I really I can keep it to a range as I have to take note of the heat dissipated by the lm317

regards,

Messlia
 



Keep input voltage to LM317 minimum 9-10V, use small heatsink or mount LM317 on metal case of device and all will be ok.


Best regards,
Peter
 

With the of lm317 to charge the li-ion batteries... what should be the ouput voltage to charge the batteries.. I want to charge the batteries directly not through the cell phone.. if I am using a 3.7V li-ion battery.. do I need to being down the voltage to 3.7v..
 

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