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

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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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91 Discussions


Question 8 months ago on Step 6

So I have a string of led lights run on 3 X 1.5 aa batteries. I buy a gizmo from ebay that lets me reduce the usb input voltage 5v down to 1.5v OK lights are on and bright BUT they are shimmering. Is this right. If I swap the wires over does not work at all SO ???

1 answer

Answer 3 months ago

You need to draw a certain amount of current to make the USB port work. Put a resistor in parallel with the buck converter to fix this


3 years ago

sir can I have help ?
my laptop usb port don't produce enough power output so even mouse I can't use it all of my port in laptop didn't work i cant copy any file to/from flash drive, when I insert optical mouse it just blink the red light and didn't recognize at all how can i fix this sir
sorry for my bad english

1 reply

Reply 4 months ago

your laptop USB outputs should produce enough energy...
there might be something internally wrong. IE bad capacitor, poor solder, etc..
ill try to get back to you on this with some solutions.


3 years ago

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 ?

2 replies

Reply 2 years ago

Some portable USB chargers give more power, but yes.


Reply 4 months ago

Generally the ones i see have 1 Port at 5V and a second at 2.5V.
i just made a wireless, rechargable LED RGB Lamp using a Portable USB charger that i got for $5 from walmart.


Question 7 months ago on Introduction

What if I'm powering 1.5v will this work. Plus how could I run this through my AUXILIARY on my car stereo?


8 months ago

so i have a wall powered led light, and the socket only outputs 4V, so will i be able to wire up a usb to this light?


11 months ago

Thank you, This helped further my Mad Engineer complex. Much appreciated.


1 year ago

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


2 years ago

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.


2 years ago

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

Reply 2 years ago

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.


Reply 2 years ago

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?

Reply 2 years ago

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.


Reply 2 years ago


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!


Reply 2 years ago

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.


3 years ago

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

Reply 2 years ago

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.