Apologies if this is basic –

But can you save electricity by charging devices from a USB port on a pc rather than use the AC – DC USB mains device? Just thinking of the environment 🙂

Apologies if this is a complex issue, just after the basics. I know there’s different USB charge rates depending upon USB version (MAh) which will charge at different rates, so arguably a mains device may charge quicker – just looking at the economics – I guess higher MAH may work out better, depending on the time vs output ratio’s.

thanks

Not really, you are still using ‘x’watts of power regardless of source. Only difference is efficiency of the power supply.

edited to add some scenarios:

Little usb power supply might be efficient for the power it produces. Or it might not be.

Is the PC on anyway or are you leaving the PC on to charge the devices? (very inefficient in the latter)

Or does your PC have an always on usb socket (my laptop does and I use it to charge my phone when out). In which case is your PC power supply more efficient than the usb one when supplying this little power or when recharging the laptop?

ok – thanks. thats that then 🙂

nope, USB output disables whilst pc not powered although there maybe in Win7 a way to change this, maybe..but probably not

Would I be right in saying 240 AC to low voltages and low USB current is likely to be pretty inefficent as there’s so much difference? therefore if the pc is on already the USB direct may be the way to go..

maybe

Really? I can’t think this will be the biggest Eco/ energy issue in your house/ life. Get out on your bike……

Get a solar charger

Switch mode chargers are pretty efficient. Were talking a few pence of electricity. As above, look for other ways to save electricity or be more eco. There will likely be plenty around the house.

nope, USB output disables whilst pc not powered although there maybe in Win7 a way to change this, maybe..but probably not

Some do, some don’t. See Sleep and charge ports.

nope, USB output disables whilst pc not powered although there maybe in Win7 a way to change this, maybe..but probably not

It’s a BIOS setting on my Lenovo, and yes it does charge phones when the laptop is off. However not all phones, for some reason. And it’s only one of the ports, the yellow one.

it does charge phones when the laptop is off. However not all phones, for some reason

That’ll probably be the power rating, some of my older USB chargers don’t generate enough power to charge my current phone.

It’s not, I think it’s some kind of random hardware issue. It supplies plenty of current and charges phones old and new – just not my old Motorola.

Charge it at work – job done 🙂

It’s not, I think it’s some kind of random hardware issue.

Some USB ports keep the power on when the laptop is off. Some laptops show which ports do this with a yellow insert, as molgrips says, Dell use a slightly different USB logo.