You use USB cables every day — to charge your phone, to play music in your car, maybe even to store large Photoshop files on an external hard drive instead of in the cloud. But you’ve probably never stopped to think about how they actually work.
It’s not complicated (at least compared to some other tech), but it’s pretty cool.
If you look inside a charging cable, you’ll see four wires. The wires that provide power are red (positive charge) and black (ground). The data wires are white and green, called “data plus” and “data minus,” respectively. The connector is engineered so that power wires are closer to the tip than the data pins. That’s to give your device power before it starts transferring data.
When you plug one end of the cable into your phone and the other end into your charger, you’re completing an electrical circuit.
That allows electrons to flow from the wall to the charger, travel along the surface of the copper wire, through your phone’s battery to deposit the charge, and then back to the charger and wall again.
Data transfer is a little more complicated. Instead of creating a circuit, data wires have opposite polarity on the same frequency, meaning they are mirror images of each other. So data plus pushes information to its destination — like when you’re moving music from a laptop’s iTunes library to your phone — while data minus — is working the opposite angle. This configuration helps eliminate noise on the wires and maintain a clear connection.
All that behind-the-scenes communication happens simultaneously, letting you charge and sync (transfer data) at the same time.
Most cables are designed this way, so when they get old or beat up after a lot of use, they typically break down the same way, too. Once a cable has been flexed to the max, its wire strands break, and a short- or open-circuit occurs.
Cheaper cables are usually made with bare copper, which breaks down more easily and tends to fail sooner. Premium cables are typically made with tinned copper, which makes them more durable and resistant to breakage. Tinned copper is also easier to solder to the printed circuit board inside the charger head, which helps extend the cable’s lifespan. There’s a lot that goes into the design of a premium cable, but quality materials give you a cable that costs a little more but will last a lot longer.
One other thing to note is the difference between Micro USB and Apple Lightning™ cables: Micro USB devices normally don’t need data wires for charging, but with Lightning cables, the Apple device will look for a certain voltage on data plus and data minus before charging starts. If you tried to use a cable without data wires, it probably wouldn’t charge an iPhone. If it did, it wouldn’t be at its max charging rate. It’s a safety feature that Apple requires as part of MFI compliance.
So that’s how USB cables work. Next time you’re ready to pick one up, think about what you plan to charge with it. If you’re using it with big battery items like smartphones and laptops, give yourself a little extra insurance and pick up a premium cable that you know is made with quality materials. Actually, do that even if you’re just using it for data transfer with a little iPod shuffle. It’s not worth risking a problem with your expensive devices to save a couple bucks on a cheap cable.