Introduction: How to Power Nearly Anything Off a USB Port

Picture of 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 ?

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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


Rellik3600 (author)2017-04-04

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.

John_135 (author)2016-12-14

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!

DanielV297 (author)John_1352017-02-16

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.

John_135 (author)DanielV2972017-02-28

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?
DanielV297 (author)John_1352017-03-02

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.

John_135 (author)DanielV2972017-03-05

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!

DanielV297 (author)John_1352017-03-08

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.

DavidB552 (author)2016-06-14

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 ?

DanielV297 (author)DavidB5522017-02-16

Some portable USB chargers give more power, but yes.

KarenC176 (author)2016-06-23

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!

DanielV297 (author)KarenC1762017-02-16

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.

Cynthiacarol01 (author)2016-10-23

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?

GTO3x2 (author)Cynthiacarol012016-10-30

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.

the4list (author)2016-09-26

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?

ad1000 (author)the4list2016-09-30

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.

3366carlos (author)2016-09-03

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

jonathanf83 (author)2016-06-25

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!

Windy Miller (author)jonathanf832016-07-21

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 :-)


KevinH245 (author)jonathanf832016-06-27

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.

NicholeB8 (author)2016-06-26

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

ouroborus777 (author)2016-05-24

5V at 500mA? Not really. While the port may supply 5V and may be rated as 500mA you can't normally get both at the same time. In addition to normal voltage drops due to cable resistance, drawing a full 500mA usually causes the voltage to sag, enough to fall below the minimum necessary to power 5V microcontrollers.

jmastri (author)2015-09-06

I'd like to take several of these (or similar) usb device charging batteries ( and connect them into an array to create a minimum of 36V and channel that to power a speed controller for an electric vehicle (ebike). Is this possible? Any advice/direction would be really appreciated.

Question 2: if this is possible, do the amp hours added together per battery or does that stay a constant? For example, a battery has 2 amp hours - if I have 5 is it a total of 10 amp hours or is it still 2 amp hours?


J.p.V1 (author)jmastri2016-05-18

Mr. Mastri, Try using a Yuasa motorcycle battery, or maybe two, strapped together to create the needed voltage, current, etc... DON'T use a USB port! You'll burn it out... Yuasa and others like it are lead-acid or advanced types of lithium or similar deep-charge batteries that are designed for high current needs... This is what you'll need for any motor-powered device; scooter, etc...

IrwanI2 (author)jmastri2016-01-11

You better off with LiPo battery. Each cell battery has the max voltage of 4.2V. You can google 10 cell lipo or 10S LiPo.

Camb0 (author)jmastri2015-12-06

First of all, let me say I'm just finishing up my undergrad in physics, I don't have a ton of hands on experience with this so please don't take my word as gospel, these are just my thoughts and it is entirely probable that they are not completely correct.

Now if I understand your question correctly you want to try and power an ebike with a bunch of anker power cores (or some similar battery) wired together. I don't know how your speed controller will work but as far as creating a power source here's how I would approach it:

Voltage increase is additive when you wire batteries in series, so wiring 7 or 8 of those 5V batteries in series should give you 35-40 V output.

To answer your second question, wiring them in series like this will not increase your battery life, but you can do this by wiring them in parallel.

this tutorial - in particular the section on batteries joined in parallel and series - should give you some insight into what you're talking about doing.

Another thing to keep in mind is that those batteries are only capable of outputting 4.8 amps, so if your scooter needs more than 168 W (at 35V) or 192 W (at 40V) then you'll need a parallel configuration to provide enough current.

Camb0 (author)Camb02015-12-06

Ah but I just realized the input power is regulated on those batteries so I don't think wiring them together would be as simple as wire together two AAs..

chrispbarlow (author)2013-03-14

Sorry to resurrect an old discussion, but this is a dangerous thing to say: "So to power something off a USB port it has to be under 5 volts as thats how much a USB port gives out " I think the "How Many Volts ?" step needs to be expanded on.

Voltage is controlled by the supply (the port in this case)
Current is controlled by the device connected to the supply

The port SUPPLIES 5 V
The device has to be rated at 5 V or ABOVE (if it is rated too high, the device won't function as the port won't supply enough voltage. If the device is rated lower than 5 V, you risk damaging the device, unless you limit the voltage before the device)

The device must DRAW no more than 500 mA at the voltage supplied. Remember that Power (voltage x current) is always constant to the device. This is important.

Say you have a device rated at 7 V, 500 mA, 3.5 W
If you supply it with 5 V, assuming it can handle the voltage variation, it will still draw 3.5 W.

So, P = VI, therefore I = P/V
I = 3.5 / 5
I = 0.7 A (700 mA) which is too high for your USB port.

So to check if you can power something:

First check the Voltage rating of the device is 5 V or OVER.
If it is 5 V exactly, check the current rating is 500 mA (0.5 A) or LESS

If the voltage rating is over 5 V, use the power consumption (calculated from the RATED voltage and the current if necessary) to calculated the new current draw at 5 V. If this is under 500 mA, then you can plug in :)

You go some way to explaining this, but saying that the device needs to be 5 V or under is incorrect.

WilliamM201 (author)chrispbarlow2016-03-31

Chris, you seem pretty knowledgeable about this topic. I have a specific question that may seem vague at first. I am looking into purchasing a device that powers usb devices via fire, putting part of the device in heat or flame and it harnesses the energy and charges usb devices. I was hoping that I could use this device to charge a few other things like rechargeable batteries or a laptop or an led lantern, but they do not have the connections to "plug" into the usb port. These devices only have normal wall ac type port. I've been looking around if there are any usb to ac power adapters or converters out there and I'm not seeing anything. Something that essentially is backwards engineered to work the opposite direction, no matter the slow power transfer it may cause. Basically, is it impossible to plug a normal ac wall battery recharger into a device that is meant to only power usb devices? Are there any devices such as this, like the reverse of AC to usb adapter, but for small output and devices? Thanks for any ideas or responses you might have.


tinman04 (author)WilliamM2012016-04-01

Your local power plant already converts heat into electricity, unless it is solar, wind or hydroelectric. The power plant is big because of the inefficiencies involved. There are devices that generate electricity by heating up two different metals (the Seebeck effect) but they are pretty inefficient compared to the turbines a powerplant uses. Next because a USB is a low voltage device (5V vs 110V or 240V) each electron does not have enough "pressure" behind it to do much work. This is why you will never find a USB powered toaster or soldering iron. You cannot generate enough heat to make it worth your time.

imkwl12345 (author)2010-10-25

hmm... you said..: Power almost anything off USB Port, well powering my house didnt work. just for future reference.

StopShootingA (author)imkwl123452016-01-27


thanks for the laugh

sucked m right onto this page as well

One thing tho, you would have to power the usb device to a generator or your neighbors house

AyushK12 (author)2016-01-13

what type of circuit is this

JackM74 (author)2016-01-09

So it seems that if USB is 5v DC 500mA, and I have a device that is rated at 5v DC 500 mA, I should have no problem powering it. But, could I power it with a Universal Power Backup / USB Charger that is rated at 2600mAh ? I am trying to make the device portable, rather than have to plug it in. Thanks ...

MicahL3 (author)2015-10-25

Thank you for this instructable. You can also use a usb wall charger for more current. 1000ma is common but check the label on your charger.

kmikeweb (author)2015-10-22

I want to use the USB port to power or recharge my laptop when the battery is low. What adapter should I buy?

TianaB (author)2015-10-21

Is it possible to use a USB cable connected to an induction charger - which then charges 3 AAA batteries?

GavitAtul (author)2014-12-27

Say, can I run a 100W subwoofer from a USB 3.0 port using this method??

mdsuave13 (author)GavitAtul2015-10-09

No, wouldn't provide nearly enough power..

4264 (author)GavitAtul2015-01-01

I'm no expert, but didn't he say:

"Therefore the max load is 5v x 0.5A=2.5. Watts. (W=VxI)"

could of course be misreading this somehow, but I think the max out is 2.5 Watts draw. I am, however, certain you
won't be able to get 100W when my whole laptop is running on 16 right

Then again certainty does not assure correctness, but I hope that helps somehow.

GeoffreyS2 (author)2015-07-02

I think that more power can be provided via an AC power adapter for charging phones. Unlike a direct connection to AC power, it is already transformed to a safe amount and DC.

legendlcox (author)2015-02-19

Not all USB ports are created equal. In recent years of smart devices the output of a usb port can be capable of something like 2.4amps at 5v. This is used for larger devices such as tablets and phablets. I am trying to find out how to build the circuit that tells the usb port how much amps to provide. I have a RAV power 15000Mah battery pack and 15 w solar power that use something called iSmart. Which turns the pack off after the device is charged. But I want to make an adapter so I can power items that aren't usb native with a barrel connecter. I just need to figure out how to tell the chargers how much juice I want, and how to deliver it.

I just posted a question asking something along the same lines. But I think I can answer your question. The amount of current that is delivered will depend on the circuit board you are powering. I'm trying to use a USB battery pack to have a convenient way of making Raspberry Pi and Arduino projects portable. So if you are powering motors, servos, and such, you will need something beefy enough that can handle not only the voltage but that kind of current. If you are powering small relatively low power components such as sensors and a few LED's you can use a much more light-weight power source. The battery will not put out more current than what is required by the circuit (unless you have a short somewhere). I see that you posted this a month ago. If you've gotten a different answer since then, let me know. I'm a newbie and always looking to learn.

AhmedE21 (author)2015-03-29

Hi, can I use this method to power a circuit that is now running on a 9V battery. I would like to be able to plug in the usb port to my laptop and the circuit to work. As I said, the circuit currently runs on a 9V battery and powers 3 fans, an LCD display and 4 LED's. Any help would be much appreciated!

That depends on the voltage required to run everything. The forward voltage for the LED's should be around 2 volts. If you are using a little 16x2 or 24x4 character LCD, then the 5 volts should be OK. You'll need to calculate the current for each of those. You need to know what the minimum voltage requirement is for the fans. If they work on 5 V, great. Then you need to calculate how much current they require. To calculate the current for the fan motors, simply hook up an ohm-meter to the fans to get the resistance of the motor coils and then use ohm's law to calculate the current. It also depends on how you have the circuit arranged. For instance, if you have all 4 LED's in series it will require at least 8 V (2 V for each) and that's not a good way to arrange LED's anyway. I would hazard a guess that running 3 fans will take more current than the typical laptop usb port can handle.

justanothernewbie (author)2015-04-15

Want to use a portable USB power supply (like the kind you use to recharge a phone) to power a circuit board. I got a couple of them from Radio Shack and made an adapter cable that goes from the USB to a 0.5 mm barrel connector so I can just plug it into a circuit board I'm controlling with a Raspberry Pi. It works great for a few minutes but then it auto-shuts off. I think that there is some sort of circuitry that detects whether the data lines are in use and if not it shuts down to preserve battery life. Does anyone know how to bypass that to keep the power on? I'm thinking that all it requires is one of the data lines to be connected high or low but I'm afraid I might fry something if I try things blindly. Does anyone know the answer to this? Thanks!

fabelizer (author)2015-03-09

When cutting ans stripping and soldering the cable, it should be disconnected from all power. It is amazing what people can do with a little knowledge!

XnoronxX (author)2015-02-23

legendlcox i recommend a "voltage controlling device" that uses a dial so oyu can set what ever voltage power you need

acronis028 (author)2014-04-29

how to make usb output by 12v on PC >> i know that is already 5v . it is possible to convert 5v to 12v dc? any one can help me for this?

Khanz92 (author)acronis0282014-10-14

use a boost converter circuit. you can easily find. 5V to 12V boost converter. Try making it yourself

Khanz92 (author)acronis0282014-10-14

use a boost converter circuit. you can easily find. 5V to 12V boost converter. Try making it yourself

About This Instructable




Add instructable to: