Peripherals Are all USB power plugs created equal?

I've got an increasing number of gadgets that have a usb lead that doubles up as a power lead by plugging it into a 3-pin plug (that goes into the mains).

I know they have varying power needs - my Asus Transformer, for example, doesn't charge plugged into my PC because usb sockets don't give enough power to do so, and so must be plugged into the mains. But I admit to being a bit hazy and nervous around electricity. Can I just carry one plug socket around, with the requisite assortment of usb leads with proprietary connectors? Or do I need lead + plug for each item?

Thanks for any help

Cara

 

As long as you don't buy a 10p one from Azerbaijhan, they're all pretty much the same thing.

 

Thanks. Wasn't sure if there was gubbins in the plug (highly technical term...) that was attuned to the power supply demanded by the product.

If anyone has the patience to educate, where does it happens that the power is stepped down? Does 240v go into my Kindle/Galaxy S2/etc and get dealt with in the device?

 

No that'd blow a hole the size of a squirrel right through your face, or so I'm led to believe lol The stepping down is done in the mains plug adaptor.

And everything that runs off USB is 5V. If it's not, then it'll have its' own cable and probably a proprietary end so you can't blow it up

 

yeah computer usb port is limited to 500ma.. the wall socket converter seems a little bit faster.. we have a socket charger that definitely charges our phones quicker than off the computer usb ports

the car usb charger is about the same as the wall socket.. haven't measured the power output though.. but it's definitely higher than what the pc puts out

 

USB contains 4 wires. 5v, gnd and the 2 data wires. In usb charging the 2 data wires become voltage negotiation wires. So depending on the voltage on the data wires the device can determine if it's plugged into a usb port and only draw 500ma for trickle charge or it's plugged into the mains and draw 1000ma for quick charge. The actual cable is the same.

If the device tried to draw full power from a usb port it would likely damage it badly.

 

Thanks, really interesting stuff cos it's all been a bit of a mystery to me. For instance, my Samsung phone charges r e a l l y slowly from the PC, but very quick from the mains. The Transformer won't charge noticeably at all from the PC (although I believe it does if plugged into USB3....but I might've made that up) and again, pretty fast from the mains. My Kindle, otoh, *seems* to charge about the same speed whether it's usb or mains, but maybe it is faster on mains - just doesn't need charging very often.

...maybe I just haz too many gadgets. *blush*

 

The current spec was raised from 500mA to 900mA for USB3, so you're not making that up...