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.

<p>did anybody built this thing ? Does it really work with the two resistors ? I want to do this, but I cant explain it to myself how it works with the both resistors, so the current won&acute;t got to the data Pins, because the both resistors are directly connected over + and - so can anybody explain it to me, or was i wrong to now what i knew about electricity ?!?!</p>
<p>It's a voltage divider and will provide both data pins with 3.75V of useless voltage. Some chargers did provide on those pins some voltage in order to indicate how much current can be drawn by device, but I don't think it is used any more. I have USB cable for charging only and internally it has just 2 lines, so unless they have soldered SMD resistors on both connectors - it doesn't provide any power on those pins. I'm too lazy to check them, just in case...</p>
I have the same problem !!
<p>good job.</p>
<p>This comes in really handy. I am trying to figure out how to keep my my cell phone charged for 6-7 hours of outdoor time lapse photography, then I saw this instructable. Thx!!!</p>
<p>Hay question, Can i use &quot;IMR 18650 LiMn 2500mAh Battery &quot; in it?. i have lot of these from my ecig mod's </p><ul><li>Rated Capacity: 2500mAh<li>Nominal Voltage: 3.6V<li>Voltage at end of Discharge: 2.5V<li>Max Charging Current: 4A<li>Standard Charge: 2A<li>Max. continuous discharge current: 35A<li>Continuous discharge current: 20A<li>Pulse discharging current: 50A</ul>
<p>Yes you can! However with a step-down converter, you'll need at least two (ideally 3 and more) batteries in series in order to make it work. Another option would be to use a step-up (boost) converter, to step up the 3.6V from the single battery up to 5V. </p>
<p>I like your Instructable</p><p>Thank you so much for sharing</p><p>Rima</p>
I think I'm gonna make 1 with 2 of those litho battery's then built in...do you think that's a good idea<br>
o also...would I need to add more resistors or would it be fine<br>
this seems like a very good idea...how long does it charge a simple phone?and how much did it cost<br><br>
<p>great instructable, i would suggest a bigger box and place the lipoly battery inside..</p>
<p>Just so I understand correctly, without a lipo cutout it would be bad news leaving an ipad unattended charging on this. Is adding a lipo cutout feasible? As a novice I was going to follow the excellent instructions to make something to charge mine and the wife's I things at the same time (they tend to get charged overnight). Thanks</p>
<p>Yes, you need to shut it down when not in use, otherwise the idle-running converter and voltage display will eventually discharge the battery. The voltage alarm shown in the last step warns you when the voltage is low, but you need to be paying attention and manually unplug it.</p><p>Battery cutout - I will do some research. If I find some easy solution, I will update this Instructable.</p>
<p>I've been &quot;fixing&quot; my Apple wired chargers for use with my Android devices.</p><p>You have wired this correctly for probably 99.9% of android devices (no one cares about the rest :D ). Primarily because you shorted the data pins, which is supposed to be the USB charging port standard. You are also correct that Samsung tweaked this standard by adding 1.2volts to the data pins to signal that it's connected to a Samnsung charger and try to pull more amps (mostly for their early tablets). With the the S4 they added another signal voltage for their new 2 amp charger. <a href="https://dl.dropboxusercontent.com/u/54767697/chg_norm_and_s4.jpg" rel="nofollow"> https://dl.dropboxusercontent.com/u/54767697/chg_...</a></p><p>Now for my point. The my S3 (maybe your S4) and my Nexus7 use the smb347 management IC. It is picky when it comes to input voltage, and in the case of the Nexus7 REALLY picky. The USB standard port voltage is 5.0 &plusmn;0.25, while I believe a USB3 dedicated charging port raised this to 5.3volts.</p><p>If I was you I would raise the voltage under load closer to 5.2. Use a multimeter to measure, I love the ChargerDoctor, but they used cheap connectors it drops a lot of voltage.</p><p><a href="https://lh6.googleusercontent.com/-DjmNzk0dhIA/U753tu8IecI/AAAAAAAAqHI/L90Zt7W_x_A/w612-h816-no/IMG-20140709-WA0002.jpg" rel="nofollow">https://lh6.googleusercontent.com/-DjmNzk0dhIA/U75...</a></p><p><a href="https://lh5.googleusercontent.com/-QFaFsp2nYKg/U753u6LaLRI/AAAAAAAAqHU/1QU_fkpgbzc/w612-h816-no/IMG-20140709-WA0003.jpg" rel="nofollow">https://lh5.googleusercontent.com/-QFaFsp2nYKg/U75...</a></p><p>Before mods: </p><p><a href="https://lh3.googleusercontent.com/-ZUItDAm2gYg/U5OZgIEZaUI/AAAAAAAAer8/BkxJpJsAUnY/w1277-h958-no/IMG_20140607_185306.jpg" rel="nofollow">https://lh3.googleusercontent.com/-ZUItDAm2gYg/U5O...</a> </p><p><a href="https://lh5.googleusercontent.com/-CrfdOfmCBkA/U6Hcwc8w58I/AAAAAAAApiY/ZckeBp047-E/w719-h958-no/IMG_20140618_141229%253Anopm%253A.jpg" rel="nofollow">https://lh5.googleusercontent.com/-CrfdOfmCBkA/U6H...</a></p><p>After mods (Bridged data pins, 150k+47k resistors feeding pins with 1.2):</p><p><a href="https://lh6.googleusercontent.com/-jkukkL7Pymc/U6HW2ss649I/AAAAAAAApg8/p4rvEEEyMyI/w719-h958-no/2014-06-18" rel="nofollow">https://lh6.googleusercontent.com/-jkukkL7Pymc/U6H...</a></p><p>Charging my S3 <a href="https://lh5.googleusercontent.com/-_QW5N5NMo7k/U6Hc3EFDx4I/AAAAAAAApik/Nhif3VDZwiA/w1277-h958-no/IMG_20140618_143535.jpg" rel="nofollow">https://lh5.googleusercontent.com/-_QW5N5NMo7k/U6H...</a></p><p><a href="https://lh5.googleusercontent.com/-RPVzJCYLB54/U6Hc83ac_VI/AAAAAAAApiw/-XqcskyVdO8/w1277-h958-no/IMG_20140618_143539.jpg" rel="nofollow">https://lh5.googleusercontent.com/-RPVzJCYLB54/U6H...</a></p><p>Idle <a href="https://lh3.googleusercontent.com/-ZPEdjzzJ75g/U754XYjv7UI/AAAAAAAAqJY/HccicLhIC2c/w719-h958-no/IMG-20140710-WA0006.jpg" rel="nofollow">https://lh3.googleusercontent.com/-ZPEdjzzJ75g/U75...</a></p><p>Charging my N7, note the Nexus is programmed to be even more picky. It waits up to a minute to see if the charger is crap before switches from AC into an even higher amp mode.</p><p><a href="https://lh5.googleusercontent.com/-RiXqBZzD7M4/U754AU4N1OI/AAAAAAAAqI0/xg321j-A27s/w1277-h958-no/IMG-20140710-WA0000.jpg" rel="nofollow">https://lh5.googleusercontent.com/-RiXqBZzD7M4/U75...</a></p><p><a href="https://lh6.googleusercontent.com/-M_zktbmn0pQ/U754HlU1Q8I/AAAAAAAAqJA/EJer2sQS3Go/w1277-h958-no/IMG-20140710-WA0002.jpg" rel="nofollow">https://lh6.googleusercontent.com/-M_zktbmn0pQ/U75...</a></p>
<p>Very informative, thanks! I actually tried two 82K resistors, but it somehow didn't make a lot of difference. But it is strange, because when I measure the Samsung charger, my ohmmeter reads 82K between GND and data and also 5V and data. But when it is turned on, there's 1.2V on the data lines. So which setup do you think is better? 10K and 33K or two 82K resistors?</p>
<p>Well 2 82k resistors makes the divider put out 2.6 volts.</p><p>I'm not sure it's better then 33k+10k, it's just different. In your case you need to try raising the voltage underload to over 5.1v. All my Samsung charger spit out 5.3 volts, hell I have one that idles at 5.37v.</p><p>Note: I use 150k and 47k so that they drain less power. </p><p><a href="https://dl.dropboxusercontent.com/u/54767697/Screenshot%20from%202014-07-31%2018%3A36%3A46.png" rel="nofollow">https://dl.dropboxusercontent.com/u/54767697/Scree...</a> vs. <a href="https://dl.dropboxusercontent.com/u/54767697/Screenshot%20from%202014-07-31%2018%3A37%3A13.png" rel="nofollow">https://dl.dropboxusercontent.com/u/54767697/Scree...</a></p>
<p>Watch out, you forgot to add three zeroes to R1 and R2 values! You entered only 33<strong>ohm</strong> and 10<strong>ohm</strong>, three orders of magnitude less than the actual values. Actual 33<strong>K</strong>ohm and 10<strong>K</strong>ohm resistors only draw 0.1mA or so... ;)</p>
<p>The .2 volts you are seeing dropped is the load consumed by the display in each of the ChargerDoctors. It isn't cheap connectors, just some simple Ohms Law!</p>
<p>If you pull the connectors off and solder straight to the pads it drops less.</p><p>I realize there is going to be parasitic losses for the display and IC, but the connector loses are not negligible.</p>
<p>It is very dangerous to over discharge a LiPo battery. They are designed to be run from 4.2v down to 3.0v per cell. They can start fires and explode of improperly handled. Since this device doesn't have a LiPo cutoff circuit it will most likely over discharge resulting in fire!</p>
<p>This is the reason why I placed a voltmeter on the front panel... Also in the last step, there's a photo of a LiPo voltage alarm with a caption &quot;ALWAYS use a voltage alarm&quot;.</p><p>Yes, there is no automatic cutoff, but all it takes is to check the voltage every half an hour or so and disconnect if it is starting to get too low</p>
<p>Well I certainly hope that's enough. If you charge like I do - over night - that would be dangerous.</p>
<p>After being away in Aberystwyth camping and having our phones continually run down this is just what I need. I'm an electronics engineer and your well researched circuit diagrams and explanations make perfect sense and will save me a few problems I had not even thought about. This is one of the best articles I've seen. Well done ! - and thank you. </p>
<p>very good! I may do this myself!</p>
<p>I think in your wiring diagram is a short circiut (the connected resistors)</p>
<p>Where exactly do you think the short is?</p>
Don't understand me wrong, but the electricity search for the shortest way. So they will &quot;circuit&quot; at this point and won't go to the data pins, so I think the both must be separated?! Because the device who is plugged in closes the electric circle. Is there an other way, to understand it better (at your wiring diagram).
<p>I merked it. So I also dont understand why the resistors are directly connectet with + and - and you connect the both middle pins with one cable.</p>
<p>The resistors form a <a href="http://en.wikipedia.org/wiki/Voltage_divider" rel="nofollow">voltage divider</a>. They divide the input voltage (5V) at the ratio of R2/(R1+R2), in this case 10/(33+10) which will produce about 1.2V at the center point. This voltage is then connected to both USB data pins. The phone can measure this voltage and it then knows that it is connected to a high power charger and pull large current. &quot;Slow&quot; chargers which supply less current (1A max) have different resistors, the phone can sense it and will limit its current draw.</p><p>And don't worry, these two resistors draw only 0.1mA (Ohm's law: I = U/R = 5V/43000ohm = 0.0001A), they are not a short circuit.</p>
<p>yo creo que por seguridad y control, el voltimetro deberia estar a la salida del conversor para asegurarme que tengo 5Vcc en los USB</p>
<p>Very Nice..!!!Thanks for the cool USB Charger...</p>
<p>Would I be able to put 4 or 5 USB connectors in this? Would power it from a DC power jack. Thanks</p>
<p>Yes, as long as the DC-DC converter can supply the current. You can either buy a higher powered converter (5A models are available), or you can use multiple of these 3A converters, each powering 2 or 3 USB connectors separately.</p>
<p>Let me get this straight...you started with what you call a crappy 10A ten amp 10000ma USB charger and were not happy with that??I wish I had one.</p><p>P.</p>
<p>Nicely done; Thanks!</p>
<p>where did you get this box/?</p>
<p>It's this model: </p><p><a href="http://www.gmelectronic.com/plastic-box-kp01-z-6-p622-401" rel="nofollow">http://www.gmelectronic.com/plastic-box-kp01-z-6-p...</a></p><p>Currently out of stock, but they carry more similar boxes like that.</p>
<p>I bought it in my local electronics shop: </p><p><a href="http://www.gmelectronic.com/plastic-boxes-for-devices-4part/sort:price/direction:asc/page:/order:" rel="nofollow">http://www.gmelectronic.com/plastic-boxes-for-devi...</a></p><p>They are based in Czech and Slovak Republic, I am not sure if they ship internationally.</p>
<p>what is the dimensions of the the project box </p>
<p>Must need for camping and traveling! I'll try to make smth like this for my moped! </p>
<p>An easy way to make a template for the cutouts is to scan or photocopy the project box face where the USB ports are. Print out the scan at 100% (of course) and use that to drill the holes on the front panel. Make sure you line it all up along the edges and cut out the template. Tape it to the front panel and see if it looks correct. Once you have it in the right place mark the corners with a small nail punch or nail so you know where each one is if the template rips. Once you do that, then you can drill with your drill. </p>
<p>Nice instructable ! very useful.</p><p>Thanks</p>
nice project..well made and very well explained..
<p>wow instructables is letting me type the first tyme . with out repeating my login info 4000 tymes. u can get most everything u need at rad shack or dx.com .</p>
<p>Very well explained and very good project, nice!</p>

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