Smart Phone Wired to External Power Supply Questions

I don't know what the third pin does exactly but as for power if you can make a dedicated 3.6 - 4 DC power supply that can deliver around 1 - 2 amps that should work as a battery substitute without problems.

Why the shouting?

He had to. His battery is giving him problems!

It's usually a data terminal for the battery condition. For more info. look here or here. Pretty simple search. As far as the phone powering up in a "hard wired" configuration, thats sometime you'll have to experiment with. Like what tcmtech said, a good stable 3.6-4 volt DC power supply.

Hopefully, the room won't fill with smoke as the genie enters

I'm assuming that it's a phone you don't care about any more. If not then you may find out that the third contact may be the "Oops, sorry!" contact. Most modern phones communicate with the battery and/or charger to ensure that it is an OEM device.

If it isn't the phone logs the unauthorized usage and when you bring your failed phone in for service they check its memory and tell you "oops, sorry, you used an non-authorized device and any damage is not covered by our warranty"

my wife has a similar phone and the same thing happened to hers the mini usb charging port on the phone stopped working. So I made a charger for her battery of course you have to take the battery out of the phone to charge it

but all i had to do was hook up the positive an negative terminals to the charger and the battery would charge just fine

I would not be upset if my phone gets fried its just a extra i have

tonite i am going to try it

I searched through all my parts and the closset power supply is 5vdc at 2 amps

but I also found the car charger cord and that drops the vechicle voltage to 5vdc not sure on amp output

but i do know it has a built in voltage regulator

5 volts would be fine if you were using the phone's USB port and the phone's battery charging circuit's. But pumping 5 volts directly in the thru the battery contacts may be pushing the envelop a little more than phone can handle with any longevity.

That's my 2¢ worth

The third contact on most "non-smart" batteries is a temp sensor (usually a Thermistor in the pack, tied from that third contact to the "-" or minus terminal. Most "smart" batteries I've dealt with had 2 or more dedicated contacts for communication. I think the phone would work just fine with the right power supply connected to just the + and - contacts. The temperature sensing is "usually" only monitored for charging, so charging can be disabled if the pack gets too hot, and sometimes charging is disabled when the pack is too cold (Li-Ion doesn't like to be charged when the cells are very cold). I would set your supply for about 3.6-3.7V, and I would be surprised if the phone drew more than 300mA at that voltage. A phone being used to make a call would probably draw more current, but you said you won't be doing that. Good luck!

Tom D.

stomachbile-

Question #3, If the hard wire to a power supply idea would work. How much dc voltage and how many amps should I use?

Look at the original charger specifications, usually on the plug side or the opposite side. Voltage fed should be the output of the charger but no more than the voltage rating of the charger. Current rating should be no more than the current rating (amps or milliamps) of the charger.

Good Luck, Old Salt

He's wanting to bypass the phone's battery charging circuit and hard wire directly to the battery contacts.

dj95401-

Yes, it is understood that the connection is to the battery and not the charging circuit. Cell phones are made to tolerate some over voltage in excess of the battery voltage rating. Examples of this are when the battery is being charged the supply must exceed the phone battery to charge it. Since the phone and the charger have a common connection through the battery this voltage is what the phone operates at while being charged. They inherently have tolerances to compensate for other spikes and overvoltage situations also. Thus his 3.7 volt phone would be able to tolerate the 5 volts fed to it by a dc power supply connected directly to the battery.

If I was developing this system it would be done in either of two different ways:

1) I would use a 3.7 volt charger (with suitable current rating) connected directly to the battery terminals of the phone. I would also use appropriate circuitry to prevent an over voltage condition.

2) Since it is the USB connector on the phone that is bad and not the phone internal circuitry of the phone I would replace it. Replacement would not be in-kind but a socket wired into the phone and connected to the wiring or contacts of the old charging socket.

No matter how it is done, it needs a power source. USB chargers are probably the most frequently used chargers currently. Using a USB charger, a 3.7v dc charger or hard wiring a replacement socket will all work. Personally I would probably go with the wired socket fed by a USB power supply. If the power supply should fail it is the most available supply and can readily be changed.

Another fact not given in the question is how was it determined that the current USB socket is bad? If not checked thoroughly and methodically the problem could be in several other components.

Good Luck, Old Salt

Thanks for all the help I got it to work no puffs of smoke or fried electroncs smell. I went with the usb charger sugestion I attached the usb positive and negitive wires to the battery contacts in the phone. The pos and neg are the two outside contacts the middle contact was the third contact in question. I tried several usb chargers before my phone found one it liked all were 5vdc 1000ma It ended up working with a HTC charger. Phone works great the only issue is a box pop up that says battery not suported see owners I hit the ok button in the box goes away. No other issues. I left the sim card in and the sd card. I ended up leaving the middle contact alone and also the data wires in usb cord. I drilled a hole in the back cover for the cable and hot glued the cable in the empty battery compartment. That was a great idea using a usb charger just for fun I pluged the phone into several devices with usb ports. works good with a car charger. Would not work with computer. Almost worked with a wii starts up but shuts down right away. I rember seeing somewhere someone got a smart phone to work with AA batteries might be fun to experiment with that idea. Thanks again for all the help. I have tons of project ideas I want to build just for fun.