Intro: Dual USB/Firewire 400 Power Bank
I have a lot of devices (cell phone, iPod, portable stereo, etc) that need to be charged on the go. I've wanted to make a reliable, portable power bank to charge these devices when I don't have access to a wall charger. Another problem is that I have a 3G iPod that only charges via firewire, an option that doesn't seem to exist in todays retail portable power banks. So, I figured I could make my own relatively cheap!
What you'll need:
-Housing (mint tin, wooden box, plastic project box, etc)
-Battery (I used a 3.7v 1500mAh rechargeable lithium polymer)
-Charger (If you choose to use a rechargeable battery)
-USB 5v boost converter
-12v boost converter (For the firewire port. Firewire iPods need anywhere between 8 and 30 volts to charge)
-Female firewire 400 (6 pin) connector
-Switch (I used a 6 pin DPDT ON/OFF/ON toggle switch in order to switch between the firewire and USB charge ports)
-Status LEDs (Optional)
-LED bezels (Optional)
-I got some rubber dust covers for all of my ports for when they are not being used, but obviously they're not necessary
-Resistors (Only necessary if you are using LEDs. Resistor value depends on LED voltage and current ratings)
-Sharpie or other marker
-Heat shrink tubing
-Drill with various sized bits
-Epoxy or super glue
Here we go!
Step 1: Design
There are many variables to consider when choosing a design for your charger:
1. What battery capacity do you want/need?
2. Do you want a single USB port or multiple ports?
3. Do you need a firewire port? (Most devices these days don't charge over firewire, so unless you have an older iPod, you probably won't need one.)
4. What type of enclosure do you want? (Metal, wood, plastic, etc.)
5. How large or small do you want your power bank to be?
The easiest way to answer all of these questions is to source out the parts you think you want and obtain their dimensions. This will give you a pretty good idea of how large an enclosure you'll need. Batteries come in all shapes and sizes. If you'd prefer as small an enclosure as you can make, choose a lower capacity lithium polymer battery. If size isn't an issue, then choose a larger lithium polymer battery, AA batteries, or even 9v batteries.
Once I had sourced parts and had a fair idea of which ones I wanted, I made a few sketches on a pad of paper and found the best way to orient all of the components in order to be able to use the smallest tin possible as an enclosure. I then went on eBay and searched for tins until I found one that met my requirements. The tin size I ended up with was 100mm long, 60mm wide and 12mm high.
I find making scale sketches is the best way to determine your needs and also to be absolutely certain that everything will fit in the enclosure you decide on.
Step 2: Gather Parts and Tools
Now that you've decided on all of your parts, get them all together and ensure that they all fit in your enclosure before you get too far into things.
Once you're satisfied with everything, take a photo of it for a quick reference in case you forget how you wanted it all to be laid out.
Gather your tools and roll up your sleeves!
Step 3: The Schematic
Definitely a good idea to have a schematic before you start cutting wires and soldering things. Here's mine, but keep in mind that unless you use all of the exact same parts as I did, yours may need to be modified a bit from mine. This is more just to give a basic idea of what things should look like.
Sorry for my crude schematic. I'm not the best drawer and couldn't find my ruler haha.
Step 4: Modify Components
If you have any parts for your project that need to be taken apart or modified in any way, now is the time. In my case, I had a male USB to female Firewire 400 adapter that I needed to disassemble in order to get my Firewire connector.
I first used an x-acto knife and cut all around the outside edge of the plastic that was dividing the two connectors. I then gently pried the two halves apart to expose the internal electronics. I then just cut the wires connecting the USB to the Firewire port.
Step 5: Solder Components
I'll walk through soldering the components in my particular device, but obviously yours may be different if you're using different ports or battery configurations.
1. Solder/connect your battery's positive and negative wires to the 'batt' input of your battery charger.
2. Solder the positive and negative wires from the output or 'load' of your charger to the centre terminals of your toggle switch.
3. solder two wires from the terminals on one side of your switch to the positive and negative input terminals of your 12v boost converter with one of your status LEDs in parallel with the proper resistor.
4. Solder two wires on the other side of your switch to the positive and negative input terminals of your 5v boost converter with your other LED soldered in parallel with the proper resistor.
5. Solder two wires from the positive and negative output terminals of your 12v boost converter to the power and ground terminals of your female firewire connector.
Note: Here is a link to a handy LED resistor calculator if you are unsure of what resistor you need:
Step 6: Prepare the Enclosure
Now that you've got all of the soldering out of the way, you can prepare your enclosure. I chose to have my USB and Firewire ports, along with the switch and status LEDs all together on the front of my tin. I also needed to have access to the Mini B USB port of my LiPo charger at the rear of the tin.
First, measure all of the areas of your enclosure that you'll need to make holes or slots in and mark the centre points of those spots with your marker.
To avoid having the drill bit skate across the metal or plastic, it's a good idea to make a mark with an awl or other sharp object before drilling.
Once all of your holes are drilled, you can either use files or a dremel to cut out the slots for your USB and/or Firewire ports (I chose to use a file for better precision).
Step 7: Insulate Enclosure
If you're using a metal case for your project, you'll need to insulate it before placing the electronic components in to avoid shorting it out. If your enclosure is made of wood or plastic, you can skip this step.
I simply lined the inside of my tin with electrical tape. Easy enough and works fine for all intents and purposes.
Step 8: Mount Components
Before mounting, it's not a bad idea to test your charger out to ensure there aren't any unforeseen issues that need attention. If everything works, great! If not, check all of your connections.
I simply used a small dab of epoxy glue on the bottom of each component to secure them. Epoxy glue is very strong, but by using just a dab on each component, it shouldn't be too difficult to remove something if it needs servicing or replacement at some point. A good alternative to glue is silicone. It is much easier to separate than glue if you ever had to remove a component.
Step 9: Charge It Up
If you bought a new LiPo battery for this project, charge it fully before using it.
While it was charging, I added some little stick on rubber feet so the tin wouldn't slide around on smooth surfaces.
I also had some rubber dust plugs for all of the ports which are good for when you're not using it or when it's in your pocket.
Step 10: All Set!
Now you've got yourself a brand new and fairly inexpensive power bank to charge all of your devices on the go!
The pictures show that it's compatible with pretty much any USB charged device.
Hope you enjoyed this instructable :)