I’ve ordered some USB charging leads for various portable devices, mainly because I’ve already got mains-USB and car-USB power adapters (they came with a bluetooth headset that charges from USB) and I agree with things like this:
“management of an individual charger for each device is becoming a pain in the backside. Since the USB power form specification is a standard, ANY charger with sufficient load capability should be able to charge ANY device.” (from USB As A Power Source)
but I’ve also heard that charging from USB is greener – or more precisely that because your computer’s power supply is running anyway, it uses less electricity to plug battery chargers onto the Universal Serial Bus than to plug in “wall-wart” DC adapters. But is this claim true?
Claims from USB recharging product sellers concentrate on the obvious “less waste compared to disposable batteries” strength, although some smarter chargers cut power to charged devices – it’s not clear whether the mass-market USB battery chargers do this, but the reasons and the electronics don’t look that complicated. China (not famous for environmental protection yet) now requires USB-charging of mobile phones while a mobile phone industry body has recommended the same approach in general.
However, there are concerns about whether Power over Ethernet is making networks less green, which might be true for USB if devices demand more high-power sockets and device makers don’t include intelligent control electronics (which people generally don’t want to pay for).
Is USB charging greener than mains charging? I’m not sure and I haven’t found any great answers – can you?
I guess in the worst case, I can try some tests with a power meter later…
Loading ...
5 comments so far
1 ssam // Aug 22, 2008 at 12:16 pm
the max output of USB is 2.5 Watt (0.5 amp * 5 volt). charging small gadgets is not a huge power drain.
If you want to reduce the amount of power you use, there are plenty place in your home where you use/waste more.
My DVD+VHS+projector all switch off use 15W. so switch them off at the mains is more of a saving. Not filling the kettle more than you need is probably also a bigger saving.
2 AlexH // Aug 22, 2008 at 12:34 pm
I think USB charging _can_ be greener, but it depends on your PSU: in general, having a relatively beefy but efficient PSU is supposed to be the best idea, and in that scenario charging over USB isn’t adding much to what it’s already doing. I suspect the main benefit would be in the cutting down of the number of PSUs in a household, though – even when turned off, there was an impact in making them. The downside is that many devices are quite ‘liberal’ in what they believe the USB power output spec. to be.
The PoE situation is a bit different I think. That article you point at doesn’t even mention some of the inherent waste in the system – you don’t want to send DC very far because you get a lot of line wastage, hence AC – so even in terms of wiring up a single house PoE is likely to be an efficiency disaster. It’s just wiring laziness imho.
3 Robert (Jamie) Munro // Feb 24, 2009 at 2:12 pm
In terms of power consumption, it’s not going to be greener or less green – the amount of power we are talking about is negligible. Yes, you get people saying things like “If everyone in the UK turned off their chargers when not in use, we’d save enough power for 5000 homes”, (numbers made up, but representative) but read that again. 60,000,000 people have to turn something off to save power for 5000 people.
A more interesting number was if you turn off your phone chargers for a year, you save enough power to have 1 warm bath.
You are not going to make your life greener by choice of charger. Get a smaller car, set the heating in your house colder, and switch of big power devices when not in use.
See this book for some real analysis:
http://www.withouthotair.com/
4 cordless kettles // Jan 11, 2010 at 10:29 pm
The power your PSU uses is dependent on whats connected. It won’t just output the max all the time. It’ll output whats needed. So by plugging in USB devices it’ll output/use more power.
So it’s not really greener. Thoguh they tend to use less power than a plugin charger.
[off-topic author URL removed by editor as permitted by comments policy]
5 MJ Ray // Jan 12, 2010 at 1:55 pm
There is some wasted power put out as heat by the PSU. If that’s not exactly proportional, there’s a little benefit in switching to USB power from mains power, as well as hopefully less turnover and clutter of chargers.