I have various USB power banks, but wanted something that would work in a total power outage and in a low/no light situation or for camping etc, so I figured why not make one in an Altoids tin?
There are plenty of cool Altoids chargers already out there, so check them out as well!
Before I begin, I want to stress that this is just an emergency charger and is not going to fully charge your iPhone or Galaxy, but it will give you enough juice to make a call or two. Plus, you can use it to power/charge any other small devices on the go. Just keep in mind that it doesn't put out a ton of power.
The idea of this charger was to always have one battery available and to have one battery always charging. I used two 240mah LiPo batteries because they can charge in about 4-5 hours by the solar panel and will provide enough power to give my phone or iPod about 1/3 to 1/2 charge, which is enough in an emergency situation. I then added a dynamo in case there's not enough light to charge the batteries. If you want to use higher capacity batteries, there's no problem besides the fact that they will take longer to charge. Also, depending on what LiPo charger you use, you may have to change a resistor depending on your battery's capacity.
-90mm x 35mm 6v, .09a, .612w solar panel
-Mini USB Lipo charger
-2x 3.7v 240mah LiPo batteries
-3v to 5v 1a DC to DC step up converter
-USB hand dynamo charger
-Mini digital panel volt meter (optional)
-2 DPDT switches
-1 red and 1 green LED
-Drill w/various bits
-Awl or punch
-Soldering iron and solder
-Heat shrink tubing
-Hot glue gun and/or epoxy glue
-Primer and paint (optional)
Here we go!
Step 1: Plan It Out
The best thing to do first is to simply draw a schematic of how you want your circuit and decide where each part will be placed in the tin. This step isn't absolutely necessary, but I do recommend it. The more stuff you have to pack into the tin, the more crucial placement of each piece is.
The only parts I didn't show on the schematic are the volt meter and the dynamo. It would have made the drawing look kind of messy and confusing. All you have to do with the dynamo (motor) is wire it to the (+) and (-) centre terminals of switch 1 (the one on the left in the schematic). Also, don't forget to wire a diode on the positive side of the motor or else your batteries will power it when switched on!
The volt meter kind of depends on what voltage you want to measure. I wanted to measure the voltage going to the boost converter. This way, it will tell me the voltage of whichever battery is powering the boost converter and will allow me to see when it's time to switch to the other battery. It will also measure the output voltage of the dynamo. If you do it that way, just wire the volt meter to the input of the boost converter in parallel with the power feed. If you want to measure how much voltage your solar panel is putting out instead, wire the volt meter to the input of the LiPo charger in parallel with the solar panel (keep in mind if you do that, it will draw a small amount of power from the panel to power the LED screen and depending on the output of the panel, it may not have enough voltage to charge the battery and power the meter at the same time). You don't have to worry about that problem if you have a 3-wire volt meter, as you can use battery power to power the LED screen and just hook the sensing wire to the panel output. If you don't want the meter on all of the time, you can wire a momentary switch in series with the positive wire and just push the switch whenever you want to see the voltage reading.
Step 2: Mark and Drill/Cut/File/Dremel Holes and Slots
Now just mark your tin with a Sharpie anywhere you need to drill or cut and then drill and cut your tin. After you drill, cut, file and fine tune all of your holes/slots, test fit all of your parts.
All of the holes/cut-outs I made were:
-Two holes in the top of the lid for the status LEDs
-Two holes in the lid for the solar panel wires
-Two holes on one side for the DPDT switches
-Two holes on the bottom for the dynamo (one for the base and one for the hand crank spindle)
-Cut-out on one end for the USB output of the boost converter
-Cut-out on the other end for the digital volt meter display
I just showed a sort of step-by-step of making the slot for the USB output just so you can get an idea of the whole process. It's basically the same deal with any slot or hole you have to make, and if I showed every single one, there would be about 20 pictures in this step!
Step 3: Sand, Prime and Paint
First, separate the top and bottom halves of your tin. Just gently bend the little tabs on the back out with a flathead screwdriver or some pliers and lift the lid off.
Next, sand off all of the paint with some coarse sandpaper and then give it a light sanding with some finer wet/dry 400 grit sandpaper and clean it off well.
Then mask off any areas that you don't want to get paint on and spray a coat of primer on. Hold the can 6 - 12" from the tin and use fast sweeping motions. A few light coats are better than one heavy coat.
After the primer dries, give it a really light sanding with some fine wet sandpaper and clean and dry it off.
Then give it a couple of light coats of paint.
*Note: Make sure you've made all of your cut-outs and holes in the tin before you prime and paint it
Step 4: Attach Dynamo
First off, you need some kind of hand charger to disassemble to salvage the dynamo (or a small motor and some gears). Every one will be different. The two most important things you have to look for are the voltage you can get out of the dynamo (you need around 5v if you're hooking your dynamo up to the LiPo charger, and as little as 2.5v if you're hooking it directly to the boost converter) and the physical size (it just needs to be able to fit inside the Altoids tin obviously). Make sure you don't use one that's too large because it still needs to be able to fit around everything else inside your tin.
Next, you need to find a good place for it on the tin. This really should be decided in the planning stage because it will most likely be the largest part inside the tin and you'll need to base where everything else goes on where you place the dynamo. I chose to put mine on the bottom of the tin near the centre. Having it there allows the crank to be folded back into the tin easily.
It took a bit of trial an error figuring out where to mount the dynamo motor and where to mount the hand crank so the two gears would mesh perfectly when the tin was closed. I ended up mounting the actual motor to the inside of the top of the tin and the crank offset slightly from it on the bottom of the tin. It just worked out that that was the best way to get the gears to mesh properly.
I chose to wire the dynamo directly to the boost converter because it puts out a relatively low voltage (not enough to charge the internal batteries directly through the LiPo charger), so when you crank it with a device hooked up to the output of the boost converter, it will charge it directly.
Once you've decided on where you're putting it, drill one hole for the base of the dynamo and another for the spindle on the hand crank so it can be folded into the tin when you're not using it. I used an RCA dust cap on the inside of the tin for the hand spindle to fold into just to make sure water, dirt and dust don't get into the tin and damage the batteries and other electronic components.
Step 5: Attach Solar Panel and Status LEDs
Secure your solar panel to the top of your tin. Make sure you insulate the bottom of the panel from the metal tin. After I soldered the two wires to the panel, I lined the bottom of it with electrical tape and then glued it to the top of the tin. You may want to sand the paint down a bit where you're going to glue the panel down so the glue adheres better. At this point, glue in the LEDs as well.
Step 6: Solder and Secure Internal Components
Now it's time to solder and secure all of your parts inside the tin. Be sure to somehow insulate the electronic parts from the metal tin. I used some cork to line the tin and then epoxy glued the parts to the cork.
With the Lipo charger, I did some slight modifications. The one that I got had a charging current of 1000mA, with is too high for a 240mAh battery. So I removed the original 1.2K resistor and replaced it with a 5K instead. I also removed the original Charge status LEDs from the board and used some extension wires to go to my own LEDs outside the tin.
With the two DPDT toggle switches, I wired them as follows:
Switch 1 (left side of the tin): Two output wires from the dynamo go to the centre terminals and from there (put a diode on the positive wire from the dynamo as well), two wires go to the input side of the boost converter. Also wire the volt meter to the boost converter input side if you want to measure how much voltage you're getting to the converter. You can wire the volt meter to other areas of the circuit depending on what voltage you want to measure. I chose the input of the boost converter because I wanted to know when the battery became depleted to it's minimum voltage as an indicator to switch to the other battery. The right (-) terminal gets wired in parallel to both the (-) battery terminal of battery 1 and the left (-) terminal of switch 2. The right (+) terminal gets wired in parallel to both the (+) terminal of battery 1 and the left (+) terminal of switch 2. The left (-) terminal goes in parallel to the (-) wire of battery 2 and the right (-) terminal of switch 2. The left (+) terminal goes in parallel to the (+) wire of battery 2 and the right (+) terminal of switch 2.
Switch 2 (right side of the tin): By this point, you should have wires going to every terminal on both switches except the centre terminals of switch 2. All you have to do is wire the (+) and (-) switch terminals to the (+) and (-) output terminals of the LiPo charger.
I specifically wired my switches the way I did to avoid confusion. All I have to remember if I want one battery charging and the other powering the boost converter is to flip both switches in the same direction.
Hopefully my description of this isn't too confusing. If you have any issues, feel free to contact me via instant message or in the comments section below.
Step 7: Put It Out in the Sun
You're done! Now all that's left to do is put it outside and let the sun do the rest!