Start your old mobile without battery
I think most of us have one or a few old mobiles which may lie in a corner without being touched for a long time. Most of those mobiles can still work but their batteries may be dead.
Some of the mobiles can be turned on without batteries but some can not especially for those smart phones. Because they will check for a valid battery before properly start up.
I found an old HUAWEI PLK-AL10 from my drawer and wanted to transform it into an alarm clock. But the problem was the battery had been completely dead. I had to do some modifications to fake a batter signal to make the board believe there is a healthy battery there and rely on the micro-usb power to start up.
I took the mobile apart and got the battery with which I used a multimeter to test all the pads of its connector. Here is the definition of each pad.
To fake battery signal I need at least two things:
1. Add a 10K resistor between temperature sensor pad and '-' pad. Or I take apart the battery and get the protector board to use the temperature sensor on it.
2. Add about 4.3 Volt to '+' pad to make the main board think there is a battery there.
It is pretty annoying to add a resistor directly to the main board because all the pads there are so tiny to solder. So I chose to take apart the battery and get the battery protection board. Then I soldered a wire onto the '+' pad of the protection board (before doing so we should confirm the '+' on the protection board is directly connected to the '+' pad of the battery connector). Then I found a 5V test point at the bottom of the main board and soldered a thin-wire onto it. After that, I found a diode (1N4007) and connected it to the thin-wire on the one end and the wire connected to the protection board on the other end (the diode was aimed at cutting the 5V to about 4.3V which is the normal voltage of the battery). When doing these things I pasted some insulating tape under the wire, soldering points and the diode to avoid short circuit. After all of these steps, the mobile looked like this:
I tested it with my iPhone charger. To my surprise, it didn't start up successfully, instead, it stopped at the middle of the booting process and rebooted itself again. So I tested the electric current of the charger and found that when booting the current value could exceed 1A which is the maximum current the iPhone charger can provide. So I bought a more powerful charger which supports 3A current and successfully started the mobile. Now it works perfectly and I think it didn't work with the iPhone charger but had actually worked long time before is because the battery also provided some current together with the charger. So without the battery, 1A current was not able to support the current consume.
Update:
After some test, I added a 47uF capacitor after the diode (between '+' of battery protection board and GND [for most of mobile designs, screws are connected to GND]), which can increase the stability when the power voltage fluctuates.
Some of the mobiles can be turned on without batteries but some can not especially for those smart phones. Because they will check for a valid battery before properly start up.
I found an old HUAWEI PLK-AL10 from my drawer and wanted to transform it into an alarm clock. But the problem was the battery had been completely dead. I had to do some modifications to fake a batter signal to make the board believe there is a healthy battery there and rely on the micro-usb power to start up.
I took the mobile apart and got the battery with which I used a multimeter to test all the pads of its connector. Here is the definition of each pad.
1. Add a 10K resistor between temperature sensor pad and '-' pad. Or I take apart the battery and get the protector board to use the temperature sensor on it.
2. Add about 4.3 Volt to '+' pad to make the main board think there is a battery there.
It is pretty annoying to add a resistor directly to the main board because all the pads there are so tiny to solder. So I chose to take apart the battery and get the battery protection board. Then I soldered a wire onto the '+' pad of the protection board (before doing so we should confirm the '+' on the protection board is directly connected to the '+' pad of the battery connector). Then I found a 5V test point at the bottom of the main board and soldered a thin-wire onto it. After that, I found a diode (1N4007) and connected it to the thin-wire on the one end and the wire connected to the protection board on the other end (the diode was aimed at cutting the 5V to about 4.3V which is the normal voltage of the battery). When doing these things I pasted some insulating tape under the wire, soldering points and the diode to avoid short circuit. After all of these steps, the mobile looked like this:
I tested it with my iPhone charger. To my surprise, it didn't start up successfully, instead, it stopped at the middle of the booting process and rebooted itself again. So I tested the electric current of the charger and found that when booting the current value could exceed 1A which is the maximum current the iPhone charger can provide. So I bought a more powerful charger which supports 3A current and successfully started the mobile. Now it works perfectly and I think it didn't work with the iPhone charger but had actually worked long time before is because the battery also provided some current together with the charger. So without the battery, 1A current was not able to support the current consume.
Update:
After some test, I added a 47uF capacitor after the diode (between '+' of battery protection board and GND [for most of mobile designs, screws are connected to GND]), which can increase the stability when the power voltage fluctuates.
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