Introduction: Universal Portable USB Charger

Hello! In this Instructable I will show you how I built myself a universal portable USB charger. I am soon attending a weekend festival with camping and I realized that my crappy chinese "10000mAh" USB power pack won't last that long. I have my phone (Galaxy S4), a GoPro and my friends will also want to stay charged. As I fly RC multirotors, I have a handful of various LiPol batteries - so why not use them as a power source?

This charger can be powered by pretty much any source from about 7V up to 30V and can deliver 3A USB charge current. I am powering it from 3S (11.1V) LiPo's, but it should also run from 2S (7.4V) LiPo's, car batteries (both 12V and 24V) and even solar panels.

The parts are readily available and I believe you can build this under $10.

Let's get started!

Step 1: Parts List

Here are (almost all) parts that I used in this project.

Not on the photo, I also used a 2-pin screw terminal and 2-pin male and female PCB headers.
I used a XT-60 connector for the main power connection, which is commonly used with RC LiPol batteries. However you can use anything else instead to fit your needs.

You will need a soldering iron, solder, files or sandpaper, hot glue gun and a dremel tool, along with basic tools (screwdrivers etc.).
You will also need a digital multimeter.
A USB voltage-current meter is very helpful for testing your charger.

Step 2: Initial Planning

I started by cutting the PCB roughly in half and making a cutout in it, so that it will fit nicely around the central standoff. Then I freely placed most of the components inside to get an idea on the overall layout.

As the 3 USB sockets are the main feature of the entire device, I placed them first onto the PCB. They slightly extend the edge of the PCB.

The last picture is the connection diagram.

Step 3: Soldering the USB Connectors

This is a fairly easy step. Just drill slightly bigger holes for the USB connectors' tabs, push them in and solder them in place. Then solder together the GND (pin 4) and the connector case for each connector.

Here I added a 2-pin screw terminal for the power connection. You don't have to do this, but it makes the final assembly a bit easier.

Step 4: Wiring the Board

This step is not too hard, but you have to pay constant attention to the wiring. Be careful so that you don't swap or short together the 5V and GND rails.

Start by soldering the two resistors. These will tell your device that it is connected to a charger and can pull higher current. Note that the values may be different for various phone/tablet brands, so just google "<your device> DIY charger" and see what works best. I first tried just connecting the USB data pins together without any resistors. That worked, then I tried the 33K and 10K resistors and it worked as well, so I just used them. Also, this produces a 1.2V voltage on the data pins, which is the same as my original Samsung fast charger does. With this configuration my phone only draws 0.6-0.7A (although it can charge at up to 1.7A), but that's enough to keep it charging. (This might be because my battery is old now? I am not sure.)

Next step is to solder the power rails. Connect the screw terminal pins to the first USB connector. Then use some wire to connect all the +5V pins together and all the GND pins together, paying constant attention to polarity and any possible shorts. The wire I used here is 26AWG, which is not ideal - you should use at least 22AWG.

Then solder the data pins of each connector together and connect them to the resistors center point.

After checking (again!) all the voltages, polarities and possible shorts, you can now power it up from a bench supply set at 5V. Measure the voltage at USB data pins, it sould read about 1.2V. If it doesn't, check your wiring again... otherwise you can try charging a phone.

Step 5: DC-DC Module

We need to prepare the DC-DC step-down converter. Just solder some wire to the output terminals. Use thicker wire (at least 20AWG), I used wire from a computer PSU.

Then hook up the input terminals to a power supply (I used 12V) and connect your multimeter to the output. Adjust the pot with a screwdriver until you get a voltage between 5.0V and 5.1V.

Step 6: Front Panel: the USB Connectors

Here comes the most tedious part: doing the front panel cutouts. I first drilled a hole into the PCB for a screw, which attaches the board to a small screw standoff inside the project box. Then I slid the front panel to it's place and traced out the connectors onto it with a marker. Using 1mm drill bit I traced out the first connector, then checked if everything still aligns and repeated this for the second and third connector.

To make the actual cutouts I pre-drilled a lot of holes next to each other just on the inside of the traced lines. Then I used the same drill bit at higher rpm to route the pre-drilled holes out. Again, after checking the alignment I repeated this for the rest of the connectors.

Finally I used a square file to smooth out the edges. Notice that the holes turned out to be a bit bigger than intended, because I was drilling too close to the traced lines. Being slow and precise here pays off with nice result. A laser cutter or CNC router would be a life- (and also time-) saver.

Step 7: Front Panel: the Voltage Display and Power Switch

Next two features are the voltage display and the power switch. Once again, I decided on the layout, traced them out and used the same technique as for the USB connectors.

I added a connector to the LED voltage display, it is a 2-pin male PCB header. The voltage display has 3 leads: power (red), ground (black) and input (white), I just joined the power and input together. The other side of the connector is a female PCB header with wires going to the power input. As with the screw terminal, this is optional but makes the final assembly easier.

Before gluing the display, I slightly beveled the edges of all holes with a small file.

Then I laid down the front panel, put the display in place and secured it with hot glue.

Step 8: Wiring It Up

I soldered the female connector of the voltage display to the input of the converter module.

Then I made a input power lead from a length of wire (again from computer PSU) and a XT60 connector. I twisted the wires together. I drilled a 4mm hole into the side of the project box and fed the wires through, making a knot on the inside to prevent pulling it out.

I inserted the PCB along with the front panel. The problem was that the board wasn't pushed strongly against the front panel and inserting a USB device would push it back a bit. So I had to improvise and used a piece of stiff wire, which is bent around the center standoff, fed through the PCB and pushes it against the front panel. Works surprisingly well.

The rest was simply wiring up the power switch and input of the DC-DC module, connecting the screw terminal and screwing the box together.

Step 9: Finished!

Well there you have it! Now you can use almost any power source to charge your device!

Some improvements I can think of would be using a regular DC power jack as the input, so that you can also plug in regular power adapters.

Also, instead of using a step-down-only converter, you could use a buck-boost converter, which can operate on lower voltage than its output voltage.

Oh and if you are too lazy to spend an afternoon making this, just grab a 12V car USB charger and wire up your battery. Problem solved :D

Thanks for reading my Instructable.

Update after initial testing:

The charger performed very well. The 5000mAh battery was enough to keep 5 phones charged throughout the weekend.