Do I need to unplug USB cables to save power?

[Dimitri]

You often hear people say don't leave your phone charger plugged into the outlet after you're done charging, because it wastes electricity, is the same true of a USB cable plugged into the computer, with nothing plugged in at the other end?

 

[Darren]

The amount of electricity pulled buy a fully charged device or one that is off completely is basically negligible. It knows it's full so won't keep pulling juice. Sure it'll be absolute zero consumption when you unplug it but the difference is tiny. Same goes for USB. The only time you really want to unplug stuff that's off for power reasons is if you're going to be gone for vacation or something like that. Day to day usage, don't worry about it. Electricity is pretty darn cheap anyway, your climate control has way more of an effect and if you're worried about power consumption that would be what to change.

 

[beers]

The phone stops fully charging and goes into a trickle anyway.

A USB device at 500 mA only pulls 2.5w. I guess you could save a dollar or so per year if you cut 6 months of usage out if there.

 

[Dimitri]

What I meant is when the device isn't even plugged into the USB. So, the USB cable is plugged into the computer, but there's no device plugged into the cable.

I use the cable as an extension cord that conveniently sits on by desk, while plugged into the computer, so I don't have to go behind the case to plug a device into a USB socket, or if I want to plug my phone into the cable.

 

[Darren]

I mean I guess I can't fault you for asking but that seems like pretty common sense that a cable plugged into nothing will do... nothing.

 

[_Kyle_]

If the charger is plugged into the PC but nothing else it is not a complete circuit, meaning electricity cannot pass through it. So... what Darren said.

 

[Agent Smith]

Just your computer being plugged into the wall being powered off will probably pull an idle load more than your USB ports combined. I mean, the PSU its self has circuitry at that will have a load on the wall outlit even when the computer isn't on. If you have an USB mouse or keyboard, Bluetooth USB dongle, etc, the load will be negligible as stated. It's really something to not be all that concerned over. If you have a phone plugged into your USB ports and it's in the process of charging, then there will be a load of course.

As to wall warts, yes, they should be unplugged if not in use if you want to save a few cents a month on your electric bill. I don't even bother with most.