Is it safe to plug USB devices on 220v wall sockets?

Question

I have an ipod touch and since then I've been charging it on the PC via USB. I just want to know if it is safe to use those wall socket chargers for USB devices? Is it different on every device, or is it safe to use it on any USB device?

Solution 1

You're asking the wrong question. You don't plug USB devices into wall sockets: wall outlets provide alternating current (aka AC), and computer devices, including USB, run on direct current (aka DC).

What you do plug into the wall is a power supply of some kind -- a switched-mode power supply (for desktop and server computers) or a wall-wart (for laptops and rechargeable devices). This device has the job of converting the outlet's AC into some flavor of DC.

So you need to use a power supply that's appropriate for the 220v AC supplied by your site's wall outlets.

Charging over USB supplies 5v, 500mA DC. Any USB-charger wall-wart should output to that standard, and all devices that charge via USB should work, so all you need to worry about is whether the wall-wart can handle the input AC.

Normally, electrical characteristics such as acceptable input voltages (and amperages) and provided output voltages (and amperages) are printed on the power supply, so you need to literally read the fine print to make sure. If in doubt, it's probably safer to buy another one.

Solution 2

Apple's chargers are "universal," meaning they'll work with any country's AC power. All you need is an adapter to allow you to physically insert the prongs of the plug into the wall socket.

To determine if any given device is universal, look on the bottom or side of the unit. If something on the label reads "100-240v" or "110-220v" or something like that, it'll work. If, on the other hand, it reads something like "110v only", then it is not safe to plug into a 220v socket.

Solution 3

I just want to know if it is safe to use those wall socket chargers for USB devices?

Short answer: Yes

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Long answer:

The usb spec tells us Vbus = 5VDC, and then the device can start with 0.1A (but the device "can ask" for as much as 0.5A).

The wall socked should transform 220VAC into 5VDC.

Please note that a lot of those wall sockets that short-circuit D+ and D- and then you don't have to negotiate how much current you can draw (and as much as 1A should be ok).

If you are unsure, just use a multimeter and check that the wall socket provides 5VDC.

Good luck.

Solution 4

Should be safe for any USB device (5.5 volts I believe). It's the amperage you'd have to watch out for, but it should be fine.

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Comments

[Almir Sarajčić]

This might have been meant as a 'tongue-in-cheek' reply, but it doesn't read like one. People don't understand the relationships between electrical phenomena, and could be misled by "It's the amperage you'd have to watch out for"

[Kalaivani]

Most laptop external power supplies are now switchmode supplies.

[quack quixote]

wall-wart is more a package design than an operational designation; external laptop power supplies are considered wall-warts, in the "in-line brick" configuration (there's even a pic of one on the wiki link). you're absolutely right that they can be switch-mode supplies.

[quack quixote]

ouch! sounds like you found a brand to avoid. was it Belkin?

[ChrisF]

No - some no name brand. Claimed to be compatible with all varieties of iPod and iPhone, but clearly didn't deliver enough current.

[Brian Knoblauch]

I haven't run across one that's not a switcher in a long time. They're cheaper, smaller, and have lower parasitic consumption. There are times when a linear is appropriate, but those are atypical applications.

[Gregory Magarshak]

Can someone explain this joke in detail?

[Josh K]

It's not a joke or “tongue-in-cheek” reply. Obviously don't try to finagle a USB cord into a wall socket. @quack has a much more detailed answer above.