Coiling a USB Power Cord




Introduction: Coiling a USB Power Cord

About: I enjoy making things. My making them is usually based on necessity, the fact that it doesn't exist, and/or buying it pre-done would be way more expensive. I like all kinds of projects and find this site a v...

This is an easy way to tidy up cord that are too long or in the way. Great for the car or desk.

Step 1: Materials

USB cord for your device (Got mine at Dollar Tree)

Step 2: Wrapping the Cord

Starting at one end of the pencil, tape down one end, leaving about 5 inches of slack. Wrap the cord around the pencil, leave another 5 inches of slack and tape down. Your wrapped part should be tight and not too pulled. 

Step 3: Setting the Cord

Using the blow dryer on high, blow hot air on it until the plastic is warm. Do this all over the pencil. You can hold the pencil on one end and do this or roll it across a table and blow dry all parts of the coil. 

Step 4: Let Cool and Enjoy!

Let the cord cool until it is cold to the touch. Remove tape, you should be able to pull the pencil out and use your cord!

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278 Discussions

Nice one, it's an old idea, but no doubt many of the youngsters may not of heard of it. A very useful technique in and around the workshop, where stuff gets tangled.
Steve (ex Plastics Engineer)

19 replies

Do you mean the kind you use to start one car with another? Because that wouldn't be a good idea...

It would be ok as long as you made sure they were stretched out before you used them but with the crazy amount of current they can carry you could quite easily melt the cables if they were used whilst still coiled. I wouldn't take the risk in case somebody used them wrong.

Yea I was just wondering it this idea would work with an extension cord for my power tools. That's a lot more than a USB cable but a very small fraction of what the jumper cable need to carry (up to 1,000 amps). Power tools 15amp max.

It is inadvisable to coil power cords in this manner.The reason being that thay carry AC current and not DC.

With AC circuits any coil acts as in inductor thus increasing the impedance of the coil so tnat the I(2) R losses become greater thus producing heat.

Sorry mate, but your information is just plain wrong. If you follow this link you'll see how power cable manufactures do it. With long metal poles and industrial ovens heated to 230F (110C). It's the same process as coiling a USB cable, only on a more industrial scale.

Hey man! Thanks so much! I really needed a coiled cable for my project, but I couldent get one I needed, and hair dryer methode isnt really very good. I wanted to use oven, but didnt know what kind of temperature I needed. So thanks one more time. Now I have a coiled cable thats just like from a factory ! Chears

Yes, but....

Inductive reactance, impedance, is a function of both the inductance of the inductor and the frequency of the "signal".


- Your mains AC is 60/50Hz - so very low,

- And the coiled USB cable, or as many loops as you could possibly put in your extension cord will be such a tiny inductance,

That the reactive impedance (I in your equation) is wayyyy smaller, magnitudes smaller, than the resistance of the copper wire.

Take apart a speaker or a "wall wort" style power transformer to see how many coils of wire it takes (hundreds and hundreds...) to create a significant (in this case both reactive and desired electromagnetic effect) inductor at low (AC mains, or similar bass audio) frequencies.

I was under the impression that USB cables carried DC, not AC


The battery charging current thru a USB cord is DC. Loading files thru a USB cord, that is AC.

Data is also DC. Data goes through on a steady voltage, It just switches on and off quickly. AC refers to a waveform with a positive and negative voltage in respect to ground.

Ah, but your switching square wave "DC" data is AC. Lots of different frequencies of AC.

When you gave some serious time to kill, investigate Fourier transforms.

You'll learn that the nice square edges of your "DC" data signal have all kinds of high frequency components. That's why they put those "lumps" in your printer's USB cable. It's a ferrite inductor to reduce the high frequency radiation caused by the square waves you're talking about. otherwise they'd interfere with your WiFi and other stuff in your house.

But there is no free lunch. When you run your square wave through an inductor to reduce the high frequency emissions - you lose some of your signal. The nice sharp corners will go away and get rounded. Enough inductance and the waveform might be reduced to an unrecognizable, error filled mess.

But - no worry. The inductance we're talking about here, by adding coils to the cord, is soooo small that it's not going to do anything serious to the USB signal.

And for the guys who think that it's going to have some effect on the AC 60/50Hz (either inductive, or electromagnetic), I wish! We'd save so much copper if we could create any kind of significant effect from ten tiny coils of wire at such a low frequency. If you don't believe me, tear apart a speaker and see how many coils it takes to create enough force to move that paper cone back and forth at low audio frequencies (kinda in the ballpark of mains AC).

The "don't coil extension cords" warning is so you don't leave it in a lump and stretch it out to help the cord dissipate heart. Yes, heat. Run your vacuum cleaner for ten minutes and then feel the cord. It'll be warm to the touch, maybe even hot. But this heat is nothing magical. Just the high power/current required by your vacuum going through marginally sized wire. The current is high enough (don't get started about whether it's AC or DC, it doesn't matter here) that the resistance of the wire becomes significant. P = I^2 * R.

And while we're at it, the resistance causes a voltage drop in the wire (V = I * R) that may be noticeable in that light bulbs in the room may dim a bit when you turn on your vacuum.

Since the signal does not cross the zero line, it is basically DC, true. But when you switch DC off and on you end up with what's called "DC with an AC component".

That AC component acts in many ways just like basic AC, and it will be affected by inductances in the line just like basic AC. Put a large enough inductance in a line and the switched signal gets averaged out to a smooth DC. This method is used in some DC power supplies to filter out the 60Hz ripple. The size of the inductor needed depends on the frequency involved. A 5 Gbit/s signal would not need much of an inductor to be significantly affected.

Technically not true. AC usually refers to sinusoidal signals with an average voltage and current of zero (i.e. they swing positive and negative and average out) or at least close to zero. On the other hand you are right about these signals cause impedance. In this discussion people are being sloppy and calling any signal that changes AC.

True, but the AC is VERY low power, not like the AC from a wall outlet. So the losses would not be important. In fact, there are many off-the-shelf audio, video and USB cords that are coiled like this.

@Questor Correct; USB carries 5V DC.

how do you think you got your DC, always need AC for it,is for charging or as a mains to DC

Good point but everything is sort of AC when it is turned on and off. It is not so much "alternating" current AC "changing" current that causes the problem. Thus the arc welder example described previously. It also depends on what effect you are talking about. A coil will generate a magnetic field with DC. That's how a solenoid works.

A few microhenries at 60 Hz are not going to make much impedance.

A little physics is a dangerous thing. :-) It is not just you but all this talk about inductance is true but the effect is so small as to be irrelevant. Do you know how many windings are in a transformer? Do you know why?