If I plug in a USB wall adapter but don't have a device hooked up, will it use power?

Question

So let's say I have a phone and a USB Wall Adapter. If it is plugged up, but I don't have my phone hooked up, will it use power? And if so, will it be a noticeable amount when left plugged in for extensive periods?

score 6 · Accepted Answer · edited Jun 16 '13 at 06:34

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The phrase you are looking for is "Vampire Power." Most phone chargers will have it, but will be minimal, like a few cents a year per cell charger in energy usage. Computer power supplies will be worse. And anything that is on a standby mode, like sleeping computers, TVs, game systems (like the PS2/3, Xbox 360/One, Wii), microwaves, etc. will consume power as well, because while the main functions are off, other functions like time-keeping or waiting for a remote to turn them on still consumes power.

Some cell chargers have been designed to combat vampire power usage, and will have a ton of labels on it telling you such. One of the simplest has a modified usb port, with a spring switch that physically disconnects the power to the regulating supply when there is no usb cable plugged in. Essentially, a power on/off switch.

Wiki has an entire article here: http://en.wikipedia.org/wiki/Standby_power

edited Jun 16 '13 at 06:34

JYelton

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answered Jun 08 '13 at 07:25

Passerby

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Computer power supplies are different: with the computer turned off, there's standby power delivered to the mainboard and USB peripherals (watching for power on events). I.e. there *are* devices working. This is different from vampire power, where a device producing work isn't connected to the power supply and you have phantom loads. The equivalent question would be asking if a mobile phone turned off and connected to the charger draws current. – Alexios Jun 16 '13 at 10:55
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@Alexios Standby power on some devices are still considered parasitic, because the average consumer doesn't understand that it is supposed to work that way. True, a TV still needs some power to keep track of time (both for a clock and automatic on timers), save settings, and most importantly, monitoring the IR receiver and front panel buttons. But the average person doesn't get that, all they know is that "Hey, this tv or game console or radio is costing me 4 bucks a year even when it's not being turned on!!!" – Passerby Jun 17 '13 at 06:39

score 2 · Answer 2 · answered Jun 08 '13 at 06:15

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It depends entirely on the regulator in use, which would consume power even with no load. Some consume a few microamperes, some several milliamperes. But it would have to be plugged in for several months for even the worst to be noticeable.

answered Jun 08 '13 at 06:15

Ignacio Vazquez-Abrams

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Thanks! I was wondering if there was anything to worry about since I never unplug my chargers. This doesn't have to do with the question, but do you know if this could cause excessive heat? – Elijah Goforth Jun 08 '13 at 06:22
Excessive is relative. But generally no. – Ignacio Vazquez-Abrams Jun 08 '13 at 06:32

If I plug in a USB wall adapter but don't have a device hooked up, will it use power?

2 Answers2