Charging Cell Phone Batteries

fireball - would be an appropriate name if you tried charging it directly like this!

What kind of battery is it (NiMH etc)?

Hello,

I charge my 3.7 volt lithiums with 4.0 volts directly from a linear power supply. I have been doing this for years and it works great. I have left the batteries charging for days with no problems as the battery resistance increases as it becomes charged and current flow ceases. I started with 3.8 volts but the battery would never give me all the bars on the charge indicator of the phone. There is great info on the web about charging these lithiums, see for yourself. I would not recommend 5 volts as I have no experience with that voltage level.

HI !

Thanks 4 the reply !

I have lithium battery and its original adapter is rated for 5.2 volt , 250 mA.

So i need to ask that :

Is it necessary to supply lithium battery with contolled current power supply or it can be charged using any regulated constant voltage supply?

Thanks & best regards!

I recharge my samsung regularly this way using a 7805 limited to one amp. I do this in my office and have never left it over night. IF the battery is completely dead it will get warm when charged. If mine got hot I would stop the charging process. I realize that the terms warm and hot are subjective. In my case hot means I can not keep my hand on it. This phone and battery are over 8 years old so I don't think that this type of charging has harmed it. It is a 3.7 volt li ion battery.

Fireball,

5V is too high for Li-Ion. The maximum voltage to prevent battery degradation is around 4.2V. 4V as mentioned by Silverocks is OK, but it won't give you 100% charge, 5V, as mentioned by SilvCrow might just give you your namesake, a fireball! I hope you never leave it overnight, SilvCrow, you might not have a place to work the next day! The plug-in charger used on phones does not go directly to the battery, it feeds the charger circuitry, which will usually have a constant current cycle, followed by a constant voltage (float voltage) cycle, and then it will go to a trickle charge after a certain amount of time, this is the point that most devices will say "charging complete" or give some other indication that charging has completed. Li-Ion have a very small window of optimal float voltage. If you do charge with a power supply, set the float voltage carefully, do not allow it to exceed 4.20 Volts open circuit. The maximum charge current should not exceed 1C, meaning 1 x battery capacity, so if you have an 850mAh battery, don't exceed 850 mA charging current.

If you really have a need to charge a Li-Ion like this, please read more information about the batteries and recommended charging profiles, the dangers are too real to "guess".

One more thing, some Li-Ion packs are set up with circuitry that will permanently disable the pack if you exceed certain parameters (charge voltage, temperature, etc.), be careful or your battery could be destroyed.

Tom D.

Tom,

I have been doing this for eight years with the same two batteries. Perhaps the batteries are more robust than you think. I still get three days of use from each battery. I just remeasured my circuit. I am charging at 4.95 volts at up to 900 milliamps on a completely dead battery and have had zero problems in eight years. the charger that came with this phone broke soon after I bought it. The original circuit had one diode, one cap, one resister and a 4805 voltage regulator in it. I have matched what the manufacturer provided With the exception that I used four diodes, two resisters and a bigger cap. I am using the same tranformer. My opinion is that if it has worked for eight years I see no need to change it. I still turn off everything in my office before I leave for the night.

My batteries are rated at 350 mA

I imagine the battery pack may be terminating the charge itself. Most packs will stop charging when the voltage reaches 4.3V.

Indeed, they may be more robust than I am giving them credit for, but given the many documented cases where things have gone wrong (Dell Laptop batteries, etc.), I wanted to warn the OP of the possible dangers. I found a good PDF document from Panasonic, one of the primary manufacturers of the cells.

www.panasonic.com/industrial/battery/oem/images/pdf/panasonic_liion_charging.pdf

Tom D.