Charging a Cell Phone Battery

[AHAB99]

Hi i'm a Student and i'm working on a school project, my group and i had the brilliant idea of creating something that could charge your phone without the outlet, however we have ran into many problems and are now looking to use a DC motor to charge a cell phone battery

Mainly it'd just be nice to know first off if this is possible i know we would need a diode to keep the current flowing one way and a motor to produce more than 3.7V, any help would be greatly appreciated.

 

[audioguru]

Keep away from Lithium batteries until you learn about their hazzards:
1) They catch on fire and burn fiercely if they have too much charging current, too much charging voltage or too much discharge current.
2) The charger must detect that the battery is fully charged then it must turn off.
3) The battery must not be discharged too low or it might catch fire if charged and it might never charge again.

You did not mention regulating the charging current and charging voltage.
You did not mention using a charging circuit designed for the lithium battery size and voltage.
You did not mention shutting the charger off when it detects a full charge.
You did not mention the charger detecting that a battery is discharged too low and limiting the current until the voltage slowly rises to a normal level.
You did not mention having a thermal sensor that blocks the charger from trying to charge a battery that is too hot or too cold. It should turn off the charging if it detects the battery becoming too hot while charging.
You did not mention having a circuit that disconnects the load when the discharging battery voltage becomes low.
There are many other things to think about when you charge a Lithium battery.

Don't you have a teacher who should have taught you all this stuff?
Go to Google and look for Battery University. It has a tutorial about batteries.

 

[maxx]

You can try something based on solar panels like in this circuit based on MAX630 or something like in this circuit based on a **broken link removed**that use wind power.

 

[RCinFLA]

Many cellphones use 5vdc (like USB +5v) for charging. The phones have the charge regulating circuit.

There is one caveat. Some phones rely on the external power pack (wall charger) which is a switcher power supply, to provide the current limit that the phone battery requires for its maximum charge current rate. The reason for this is to avoid excessive charge requlator heating within the phone. The charger series pass transistor (MOSFET) within the phone just pulses totally ON or totally OFF, again relying on the external power pack to limit the totally ON state current.

In the case where the +5vdc does not provide the current regulation then the phone internal MOSFET pulses in linear mode for short duty cycle to keep the device from overheating. It takes longer to recharge because it must keep the series pass MOSFET from overheating in linear mode.

The phone internal charge regulator circuitry handles the voltage management on the battery, determining when battery is fully charged.

 

[audioguru]

Many phone Li-Po or Li-Ion batteries have built in protection circuits that are not chargers.

 

[colin55]

The energy and time required to charge the simplest phone battery via a motor (generator) will be so long that you will never fully charge the battery.
You will get bored long before the battery reaches even a modest charge.
You can buy a hand-cranked torch for $5.00 - $10.00 and modify the motor (generator) by adding turns to the armature as shown on my site to get about 5-7v output at about 200mA.

 

[krishna1234]

use solar cells this will make your project more greener..........

 

[colin55]

There is nothing more un-green than a solar cell.

 

[MrAl]

Hello,


Energizer makes such a product and i think other companies do too. You use two AA cells in the device and that charges the cell phone battery. If i remember right, two AA alkaline cells charge up a 2 ampere hour cell phone battery to about 1/2 of full charge or maybe a little more. It doesnt charge the battery to full capacity, but it makes it usable again if it went dead.

 

[second286]

Good Idea! A dc motor used as a generator-hand cranked! Pick up a hand cranked flashlight at Canadian Tire; I believe when I tested the voltage it was about 10 Vdc at fast crank. Just have to limit the voltage and current to your needs. To determine what you need to charge your existing cell battery-just analyze the charger current and voltage output, then build your generator circuit to model your charger output. Of course there will be a set crank rpm that would be required to do the job. You could design into your system a device to switch on the generated power to the battery only at this minimum crank rpm.

 

[audioguru]

I got two squeeze-crank flashlights at some kind of celebration. You squeeze and squeeze and squeeze its crank until your hand is nearly falling off and its generator vibrates as it charges something inside. It can light its two bright white LEDs for a long time or can hold a charge for months.
I took one apart to see inside and found the generator spinned by two gears but I found no super-capacitor or rechargeable battery.
I guess it uses "magic" to hold its charge.