Introduction: Portable Phone Charger
My wife recently got the LG Lucid. Much to our dismay, the battery life was gone by about 3-4 in the afternoon from a full charge that morning. She loves the phone, however, so I thought a portable battery charger might be a good solution just in case she's in a store or somewhere without a car/wall charger. This is what I came up with - my 1st instructable!
There are several of these around the net, but most people use an altoids container, a 5v voltage regulator and a 9v battery. I built one of these and it sucked. Because 9v bats only hold around 450mah at best, it charged the phone about 5%, which rendered it useless. It also uses a female USB plug, which means you have to carry around a USB cord with you, which is extra hassle. I wanted to create something that used common easy to find parts, and was cheap to build. This whole project costs around $4 to build, and it charges the phone anywhere from 25-40% depending on the type of batteries you use.
Step 1: Parts List
1x Battery box - $1.99 (I saw it at another Radio Shack for $2.29, but my local one had it for 1.99)
4x AA batteries - $.50 (I went to the dollar store and bought this 8 pack for $1)
Cell phone cord $1.50 (I found one cheap on Amazon, but make sure you get the one that fits your phone)
1A diode (these are very cheap if you buy them in bulk - probably in the 10 cent range).
Soldering iron / solder
Heat shrink tubing, or you could use electrical tape I suppose
1st, cut the cord, leaving about 3-4 inches from the part that attaches to the phone. You need to strip the cord back and you'll notice some insulation, probably some foil, and 4 wires: red (+), black (-), and green and white wires (data). Cut it so that you leave just the red and black wires remaining. The green and white wires are only for transferring data, which you will not be doing. Which leads to an interesting point - this charger cannot be used for an iphone because Apple created phones that draw current from the data cables - I think around 2v each. Even though you could make something to charge an iphone, it would require resistors to drop the voltage on these 2 cables. I don't have an iphone, so I didn't care to do this.
Cut the black and red wires coming from the battery box leaving about 1.5 inches left.
Take your diode and cut it leaving about 1/2 - 3/4 inch left on each side. (You'll notice that this is a 3A diode and I mentioned before that you'll need a 1A diode. I didn't have a 1A diode and didn't want to buy one, so I used this 3A one. But 1A is all you need. Wall chargers allow 1A.)
Before you solder the wires, you need to slip on your heat shrink tubing, and smaller one that goes on the black wire, push it towards the battery box so that it doesn't come in contact with any heat while you're soldering, otherwise it'll shrink and you'll have to cut it off and put on another. Now get a larger one and put it on both wires, but push this one toward the plug end. This one will cover both wires, the other one covers just the black one. Obviously the 2 wires cannot touch each other. The larger heat shrink tube is large enough to cover the soldered area and around the diameter of the diode, but not big enough to slip on and off the end of the cable.
* Heat shrink tubing is cheap, and if you're a tinkerer, grab yourself a box of them, you'll use them all the time. But if you don't have any, all this can be accomplished with electrical tape, it just won't look as nice.
Solder the black to black 1st, then wait till if fully cools before slipping the tube over the connection. Once on, heat it to shrink it, and move to the red. This is where the diode has to go. Make sure the diode is soldered in the right direction, otherwise current cannot pass beyond this point. The stripe on the diode represents the cathode side (negative) and it leads away from incoming current. So this side (see the picture) will be on the opposite side of the batteries, or the side that is closest to the phone plug. The solder the red wire coming from the battery box to the side of the diode that doesn't have the stripe (the anode).
Wait until fully cooled and then slide the larger tube that you had already slipped on before you soldered the diode on. Heat to shrink.
At this point, you could leave it. I decided to put one more piece of extra large heat shrink tubing on the connection, just to reinforce it. The cool thing about this battery box is that is has an on/off switch.
Put in your batteries, close the lid and charge away.
* This box takes 4 AA batteries and if you know anything about batteries, you know that non-rechargeable batteries carry a voltage of around 1.5 volts. Most rechargeable AA batteries carry a voltage around 1.2-1.3 volts. We need at least 5 volts here to charge a phone. Your USB cord, whether plugged into a wall jack or computer, will allow around 5v to pass because that is the minimum voltage needed to charge a 3.5-3.7v phone battery. So 4 rechargeable batteries would give you about 4.8v, and even though technically this would momentarily charge a 3.7v battery, especially if it's a dead battery, it will take a long time to do so and would probably only give you about a 5% charge. 4 regular batteries gives you 6v and will not only charge the phone more, but also much more quickly. Since these are cheap at the $ store, this is what I used. With the cheap ones I get about 25-30% charge from a dead battery. If I put in Duracell bats, it will give be around 40-50% charge, but this is an expensive way to go.
And you're done. As you can see from the picture, it is plugged in and is charging as indicated by the orange LED at the top. Look at the phone and you can see the battery charging symbol next to the time at the top right.
And that's it. Remember to turn the switch on!! =) Good luck.