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hardcore misery said:i've tried to cut my cellphone charger's output jack and plug it to my cellphone to measure its voltage, but the multimeter doesn't display its voltage, but it displays battery's resistance.
hardcore misery said:...and the charging circuitry is not connected to the battery?
this is one of the main problems on our project (auto-shut off cellphone charger)
the comparator should sense a voltage across the cellphone, but unfortunately we've not expected this problem.
hardcore misery said:this project is for our electronics design course...
we've not researched about charging techniques for cellphone batteries..
one question sir, if a battery is overcharged for a period of time, does it mean that the battery voltage exceeds on its rated full battery voltage?(ex. full battery voltage is 4V, if overcharged, does battery voltage exceeds 4V?)
Its good if you can design a charger for Li-ION but its really hard.hardcore misery said:this project is for our electronics design course...
This is the most important before building any battery charger first.we've not researched about charging techniques for cellphone batteries..
audioguru said:A cell phone already has a charger circuit in it.
Take the battery out of the cell phone then charge it with your own charger circuit.
If the battery is a Lithium cell:
1) Limit the charging current to what the battery manufacturer recommends. 2) Use your comparator to stop the charging when the battery voltage reaches 4.2V or whatever the manufacturer recommends.
3) Use the temperature sensor in the battery as a backup to stop the charging if the battery gets too hot because your comparator might have failed.
JimB said:I have to ask, what is the aim of the project?
Is it to improve the charging of cellphone batteries?
If so, I think that the phone manufacturers would have that well sorted by now. One of their selling points would be good battery life between charges.
Is it to save the planet from global warming from all that horrible C02 produced by cellphone left on charge unnecessarily?
If so, you need to be in at the design stage for the whole battery/phone/charger system.
As an afterthought, you could try investigating the current drawn by the phone from the charger during the charge cycle, and use that as the basis for switching the charger off.
JimB
hardcore misery said:this project is to be designed to avoid overcharging of cellphone batteries. this is just a design project for out electronics design course, in fact, tommorrow is our initial defense of our prototype( all we can present is the multiple charging system of the cellphone charger)
hardcore misery said:But how come that there are some cases of overcharged batteries due to unattended charging condition of a cellphone(a fully charged battery is left connected to a wall wart charger)