How to Power Nearly Anything Off a USB Port





Introduction: How to Power Nearly Anything Off a USB Port

Hi , this is my first instructable so go easy on me :)

So i am going to show you how to power nearly anything off a USB port

This is for the USB competition

USB runs at 5v. The max current you can draw is 500ma. Therefore the max load is 5v x 0.5A=2.5. Watts. (W=VxI) If you try and draw more than 500mA, you may overload the port which will cause it to break


Just a WARNING to look what your circuit needs if it needs a higher Voltage/current this can break your ports make sure you have got the correct details of the circuit WARNING

Step 1: How Many Volts ?

So to power something off a USB port it has to be under 5 volts as thats how much a USB port gives out so you can check this by ;
Looking at what battery is being used
4 x aaa = OK 
 4 x aa = OK

USB runs at 5v. The max current you can draw is 500ma. Therefore the max load is 5v x 0.5A=2.5. Watts. (W=VxI) If you try and draw more than 500mA, you may overload the port which will cause it to break

Just a warning to look what your circuit needs if it needs higher this can break your ports

Or looking at a the transformer and see how many votls go in to the circuit ( if your 5 or under your ok )

and you can power of the Port :)

Most electronics nowadays are under 10 V and most of them Under 5V which is good for USB

Step 2: Get Your Cable

Okay so your going to need to get any USB cable this can be a printer cable or a MP3 player cable , your going to be cutting it up so don't pick a cable that you need :P

I chose this :

Step 3: Cutting

So you have your wire , now you will want to cut it to the length you want it , you only need the Male end so the other bit can be discarded

Step 4: Stripping the Wire

Okay you will want to strip the wire to reveal the wire underneath once you have done this there should be 4 wires , you only need the red and black ones as they are the power the green and white are data so they can go :)

Step 5: Soldering and Finish

So you will now want to solder the red wire ( positive ) and the Black Wire ( negative ) to the power in to your circuit or appliance as shown below  you can also put heat shrink on the wires to make it neater :

So The Red is Positive ;   +V

And the Black Negative ;   0V or -V

Step 6: Testing

Now you've done that you should be able to test it , just plug the cable into a USB port on a computer or laptop of choice , and see :)

Thanks for viewing my instructable



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    84 Discussions

    Thank you! Informative, concise and useful.

    I have used your Instructable and came back to do it again. This time I will take pics ;) too much of a hurry last time.

    My Project, take battery operated string lights (LED) and use USB power instead.. and by the way They Light up My Room, so in a way I am using them to "power my house" LOL

    Can I also wire the USB wire to this? My goal is to use the USB socket, to send power to the female socket, so I can plug a two prong appliance in.

    Great guide!

    I'm thinking of doing this with a LED light I have attached above my tower, I turn on the light to see the USB ports on the top of my tower when I need to use them.

    I have a USB cable I'm going to use, but since the LED light uses 3 AAA batteries to light up the 5 white LEDs, I'm wondering if I need any resistors or anything added, to power the light for the 15 seconds or so per use so my PC doesn’t get damaged or anything.

    [the lights are called, 'Lightmates', I got a few of the lights themselves at a thrift-store, works great, but would like to USB power 1 or 2 of them.

    Your thoughts please?
    Thanks in advance for this great guide and reading my post!

    5 replies

    To get your super simple circuit done, you will need some resistors.

    The basic setup would be to connect a 500 - 2000 Ohm resistor to one of the legs of the LED. Connect the other leg of the LED to your USB wire and the last leg of the resistor to the other part of the USB.

    And LED has 2 pins but only works in one direction. If there is no light when you try it, don't be afraid, simply switch the legs and it should work.

    If you pick a very large resistor, there will be a bit less light. Don't do anything below 500 or it will blow.

    Good Info, thank you for the article and replying back to me.

    While I was waiting for your replay I did the cable splice and connected the two power lines from the USB cable to the negative and positive of the battery department (the 3 AAA where all connected to each other in one line, so I connected the cable to the + and - of the battery department) and I tested it by plugging it into a usb port.ends

    It works perfectly without the resistors, left plugged in ~45 sec at most I think, but is that just waiting for a problem to happen later, is that why the resistors suggestion?

    I only connect it to my pc when I need the light for a bit, haven’t plugged it into the back USB port (where I plan to plug and forget it later) yet, wanted to wait for your replay and read it and then respond before I tried that.

    Your thoughts please?

    There are 2 problems with just connecting LEDs straight to a power source.

    1: Heat in LED

    2: Overloading USB controller.

    3: You have increased voltage from 3.6/4.5 to 5v

    Number one is important. The LED can burn up internally from the high current as the magic area in it is very small and heat sensitive.

    Number 2 might become more expensive, but less likely a problem. Most PC USB ports can do a max of 5v 500mA. If you plug in a diode with any less than 10 Ohm of internal resistance it will be overloaded.

    You are also increasing the amount of power in the diode by going from AAA batteries to USB 5v.

    3 rechargable batteries in series gives 3.6 v, nonrechargable gives 4.5. By increasing voltage you also get more heat in the diode.

    Personally, I would add a resistor but its not going to kill you, only your diodes.


    I did think about the 3xAAA(v1.5x3) VS 5v USB port and the LEDs were a bit bright, that and your simple/detailed explanation really helped me, thank you!

    So I just need to get a single "500 - 2000 Ohm resistor" and I'll be ok, anyone in that range, right? Higher #/resister = not so bright LED right?

    I have some unused/sealed resistors I haven't used yet, I'll look through them and see if I can find one in that range.

    BTW: Do you recommend any color-code/resistor app for my android tablet that would help me with identifying/verifying what I use is correct?

    *just in case I can only find a loose resistor and not a sealed with info still on package*

    Thanks again for all the help/advise!

    I have tried apps, but they are really bad at reading the color codings on resistors. I would suggest either measuring with a multimeter or just read the color code using a chart like this one:

    And yes, higher resistor value is less bright. Most commonly used resistors are 1k - 10k.

    If I have portable usb charger can I assume that it will work in the same way as a usb port on a computer for this tut ?

    1 reply

    Some portable USB chargers give more power, but yes.

    I have an internal medical device, and I recharge it every two days or so, with special batteries. The external battery I use to recharge internal sacral stimulator, sits in a charging cradle, with detachable AC cord.

    The cord says input, 1OOV, 24OV, 5O to 6O Hz O.4A.

    Output, 5V, 2.OA. I have

    portable car battery jump starter, with usb ort that stores 55,OOO (yes thousand} ma. Slightly larger than paperback book. Going on 4 day wilderness trip. is there a usb to the input on this cradle., OR another option would be if USB to AC adapter exists. (Not common ac wall to usb adapter, other way around. Help, asap!

    1 reply

    Many more expensive battery packs offer 110/220v, like the Goal Zerio Yeti 150 so you can plug in just like with the wall.

    Many cheaper packs also have 12v supply (like the Goal Zero Sherpa 50)

    and you can find 12v to 110/220v inverters in many forms on amazon.

    I would not suggest modifying medical equipment yourself as it can quickly become very expensive and dangerous if something breaks.

    Your charger draws 50 watts from the wall, that is out of the realm of USB but totally possible from either of the batteries linked above.

    Hello, i have a question. I have the iihone bose speaker for the house, which has an outlet power cord, but i want to use this speaker i. A place where the only available power supply is a usb port, is there an adapter i can buy?

    1 reply

    You can't run an extension cord? Whatever is supplying the USB has to be plugged into 120 VAC anyway. The USB probably can't power it, and you'll probably stress the (assumed) computer power supply anyway.

    I have a question that you probably wont answer. I am doing this for some lights I made. the lights used 3xAAA batteries. outputting 4.5 volts. the lighs had a circuitry that resisted the voltage to the LED and on a brand new battery sent 3.5 volts to the led.

    When i changed this over to USB, it was sending 3.3 volts to the led but the led was overheating and melting the inside of the lamp.

    why would 3.5 v off a battery not melt the led but 3.3 v off usb would?

    1 reply

    If you removed the resistor the LED module itself probably has too little resistance to limit the current to a reasonable value. It's Ohm's law: I = V/R where V is the voltage, I the current and R the resistance. If you have next to no resistance then even for a lower voltage, there will be a huge current that will melt the LED module. Choosing a slightly higher voltage and adding a resistor to limit the current as in the original setup should fix the problem.

    good info. Just make sure you are not drawing more current (amps) than your source can provide. Also be aware of the gauge of wires. P=IV, I=P/V

    I just connected a 100 watt solar panel to my travel trailer. It has a charge controller, with a "load" connection. I would like to have a usb power strip in the trailer. Using the pictured power strip, I wonder if I can cut off the car adapter and connect the bare wires directly to that load connection on the charge controller. Any thoughts? Thanks...I am completely new at this!

    2 replies

    You can remove the car adapter, but remember that this will have a fuse in it to protect the circuit - if you are wiring it direct put in an inline fuse and this should see you right :-)


    Assuming your load connection is 12 volts like it is on mine, I would just hook a 12 v auto outlet (cigarette lighter) up to the load ports on your charge controller and plug your usb power strip into it. Otherwise, you will need to get a step down converter which will more than likely be just as bulky as the existing plug. I hope that helps.