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Quite similar to this one. If I'm not mistaken any impulse mobile device charger is still consuming power, when plugged into socket, but when cable is disconnected from charged device. Correct?

Does the same rule goes for power sockets equipped with USB ports for charging mobile devices (link to Polish seller):

enter image description here

I was wondering, if this kind of construction means that my socket(s) will be continously draining power, 24 hours a day, no matter if anything is connected to it or not? Or do these have some kind of power-off "switch" (meaning stops draining power when everything is disconnected)?

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    \$\begingroup\$ If the device has no physical switch the question is not if it is draining power when nothing is connected - it will drain power. The real question is how much it will drain. This can range from 0,0001 Watt to 1 Watt or even more. \$\endgroup\$ – Robert Nov 26 '16 at 14:31
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    \$\begingroup\$ Nowadays standby current is USUALLY tiny. If people really care an unswitched design can be made to draw microamps on average. Many don't care that much. | How? eg - allow Vout to trickle to say 5.5V via very high impdance and reverse diode if no load. On connection of device this is reduced and change triggers a 'switch'. Sby cct can draw essentially zero current. \$\endgroup\$ – Russell McMahon Dec 5 '16 at 0:52
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    \$\begingroup\$ This appears to be a duplicate of electronics.stackexchange.com/questions/6123 \$\endgroup\$ – Richard Crowley Dec 5 '16 at 5:29
  • \$\begingroup\$ Worthy design to make USB charging ports available on common panels. Usually one does not have a socket without a switch to turn the device on only after it is plugged in. By common sense one would keep the switch off in normal condition. \$\endgroup\$ – Abu Bakar Dec 5 '16 at 6:52

11 Answers 11

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Yes, the charger will use some standby current (unless there's a switch), but the current can vary widely depending on the charger.

I measured a dozen chargers a while ago and found the standby power usage varied from 19 milliwatts to 375 milliwatts depending on the charger. This works out to about 2 to 47 cents a year at average US power costs.

The switching power supply chip in the charger may be designed to minimize power when the charger isn't in use, for instance by skipping cycles when the load is low.

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    \$\begingroup\$ Changing accepted answer to yours, as exact calculation of "money waste" per single socket is something, I was looking for. Pity, that you answered to lately to catch a bounty. Thank you for a short, yet great answer. \$\endgroup\$ – trejder Dec 16 '16 at 10:42
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These kind of AC to DC converter will always consumme a small amout of power to maintain the control IC alive. I do not see a way around that unless your USB port has some sort of mechanical switch to flip on the converter when you connect a device. I recommend you to look around as I found this wall plug (for US 120V unfortunatly for you) that only turn on the USB charger when you lift the small window above it (mechanical switch as I said). https://www.amazon.com/Newer-Technologies-NWTPWR2U15ATRW-Nwtpwr2u15atrw-15-amp/dp/B00BGF00TO

Usually, external ac to dc power supply must have an efficiency rating from level 1 to 6 now.

CUI Inc has a nice page that explains the regulation and this tells you how much "no load" power consumption you can expect for each efficiency level : http://www.cui.com/efficiency-standards

The problem I can see is that I am not sure if your AC to DC USB power supply count as an "external" power supply. Most USB charger from a wall plug doesn't specify an efficiency level... I do not know any regulations for internal power supply...

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    \$\begingroup\$ Yes, they would count as external supplies... \$\endgroup\$ – Passerby Dec 5 '16 at 7:27
  • \$\begingroup\$ +1: The CUI link explains everything. Looks like all new walwarts must comply with DoE Level VI - 100mW in no-load mode. What kind of logo should we expect to see on these devices? \$\endgroup\$ – Ale..chenski Dec 11 '16 at 0:02
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Yes,

any charger will consume some power, even if no charging device is connected to it. As @dim pointed out, if there is no physical switch which turns the charger off, there will always be some power consumption due to the charger converting the "raw" energy into a form the charging devices can use (from AC to DC and they adjust the volt count - usually to 5V).

However, how much power is drained is something else. This depends on how good/poorly the charger is made. You know definitely that a charger is not well made, if it makes high pitched noises or gets warm when plugged in without a charging device.

If you want to know how much power it drains exactly, or which of two chargers is more efficient, there are devices like this:

An example device for measuring power another device X consumes

using it we can determine, how much energy a charger uses. It is of course not a very-high precision tool, but it should do the job for our case. Using it we can determine that the charger (I hadn't one like you showed in the image, so I used a normal microUSB charger) consumes 0.03A when charging a phone and 0.001A when plugged in without anything else (int this case, the charger did make the noise).

And this applys to basically any charger or device which does not have a physical switch or uses raw AC power. Some energy will always be lost, although it is not really enough to be something an average user should worry about (however, having a charger/similar that heats more and more up is).

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  • \$\begingroup\$ This seems to be a rather confused answer. It would make more sense if you deleted the 'no' option :) \$\endgroup\$ – Sean Houlihane Dec 4 '16 at 17:23
  • \$\begingroup\$ Just because it doesn't make a sound or get hot does not mean the charger is not using power. It can be in the milli watt range! \$\endgroup\$ – Passerby Dec 5 '16 at 7:30
  • \$\begingroup\$ Yes, those comments don't address that part I mentioned. Heat and noise are only signs if a very badly designed or failing part. \$\endgroup\$ – Passerby Dec 5 '16 at 7:50
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In the past I randomly measured a few chargers and it appears like the power consumption is usually below 1W even for larger chargers like to one for a robot vacuum cleaner when no load is attached.

I live in the EU and this observation seems to be in line with an EU policy:

4 years after the regulation is in force (December 2012):

  • Power consumption in off mode must be 0.5 Watts or less;

  • Power consumption in stand by mode which allows reactivation must be 0.5 Watts or less;

  • Power consumption in stand by mode which allows reactivation and displays information (such as a clock) must be 1 Watt or less.

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Yes, virtually all chargers and power supplies have a residual power drain when they are not supplying anything to their output. Because there are hundreds of millions of these gadgets, the no-load residual power adds up quite substantially.

Government agencies are working to require much more efficient chargers and external power supplies ("wall-warts" and "line-lumps"). The USA Department of Energy estimates that more than 18 billion KWH annuallly have already been saved by the efficiency requirements already imposed by the states of California and Oregon. And estimate that savings approaching 30x more can be achieved by making much more efficient and "intelligent" chargers which don't waste power when there is no load, or stop pumping current into a battery after it is charged up.

Ref: https://www.nrdc.org/experts/pierre-delforge/new-federal-battery-charger-efficiency-standards-will-power-americas

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    \$\begingroup\$ Wouldn't the cost of designing and manufacturing such "economical" devices (which impose extra economy on already very reduced standby power) vastly exceed the potential savings? I consider regulations of this kind highly idiotic. Why not let the free market economy to decide what kind of standby efficiency a device should have? Why should I bother about milli-Watt-hours when my air conditioning consumes thousand times more? "30x more" on 500mW won't solve energy problems. I think the focus of some divisions of DOE is highly misplaced. \$\endgroup\$ – Ale..chenski Dec 10 '16 at 20:12
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Usually these devices have an internal transformer.

In a transformer, although the conversion efficiency is very high, there are ALWAYS losses, even in no-load conditions.

The equivalent circuit is like this: Equivalent circuit
(from Fitzgerald-Kingsley).

As you can see also if \$I_2=0\$ (secondary in open circuit condition, i.e. no load) there's a current that can flow in the primary.

You can verify this assertion easily; if you have a common smartphone charger (not too high quality) you can feel it lukewarm if you leave it connected to the plug when not in use.

The passive elements represent the various kind of losses that there are in the transformer (Joule, Eddy current, flux leackage, etc) that in italian we usually call as "copper losses" and "iron losses" (translated in english, I don't know if there's a conventional english name).

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    \$\begingroup\$ This, and the feedback circuit on the secondary usually uses a resistor divider, a reference, and an optocoupler that will all leak current, and there is also some current wasted on the primary to just power the controller IC. It's not just the transformer. \$\endgroup\$ – dim lost faith in SE Dec 5 '16 at 9:16
  • \$\begingroup\$ Yes! But also in the simplest design there's a transformer that draw current. \$\endgroup\$ – Antonio Dec 5 '16 at 9:22
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As can be seen from the picture there are 3 outputs.

  1. The standard 230VAC output with earth contacts (SCHUKO).
  2. 1 power port for tablets with USB connection
  3. 1 power port for Phone and other devices.

As for 1. No power is used unless you plug in and switch on an appliance. It is a pass through connection, just copper.

For 2 and 3. These outputs supply 5 VDC up to a specific max current rate. (See documentation). Most probably with ONE so called buck converter. These units still use a very small amount of power as long as they are connected to the mains.

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All electronics consumes some power when operating, so the short answer is "Yes" it will always consume some power if there is no physical switch to disconnect the input source.

If you look at the schematic for an Apple charger, you will find it is using this controller.

Looking at the datasheet we find that the quiescent current (the current required simply to drive the controller with no load) is as high as 3.5mA.

Controller quiescent current

This is but one example; certainly there are many ways of doing this, but the technique in the above controller is very common and although we strive to minimise 'standby' power, there will always be some energy used while the charger is plugged in.

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I believe there are only two ways of converting A/C mains to the low voltage D/C needed for charging phones.

Older devices used a transformer. Theoretically there should be no drain on the mains when there's no current flowing through the low voltage side. However, inefficiencies in transformers and the circuitry used to smooth/condition the low voltage could draw small currents (milliamps) hence the need to unplug chargers.

More modern devices use digital controllers to smooth short, high frequency pulses mains voltage to average out as low voltage. These are sophisticated chips with current limiters and very high impedence components. These supply current when the battery charging circuit in your phone calls for it.

Even if you leave your phone plugged in, it will only be drawing current while it needs to charge. And without anything plugged in, ambient consumption will be negligable, less than microamps.

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  • \$\begingroup\$ If the power draw was in the nano amp range, it wouldn't be considered a problem. Problem is that it's often in the milliamp range. \$\endgroup\$ – Passerby Dec 5 '16 at 7:33
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Yes, every always-on power supply consumes power when is not loaded or in standby mode. However, the real question is how much does it use relative to your overall household consumption. Of course, some people go around the house and unplug every wall adapter and laptop AC-DC bricks, and frequently you run into discharged dead device that you happen to need right now. So the question is whether the power savings from standby PS are worth the inconvenience to have non-functional devices, reach to AC outlets to plug-unplug, or pay $20 more for super-saving standby supplies as compared to $3 for cheap Chinese box?

I just did a quick and dirty experiment. I took five laptop AC-DC adapters (Dell, HP, Lenovo,..), five 5V-12V regular wall-warts, and five 5V 1-2A phone chargers (Apple, Samsung, ASUS...), and plugged all of them (via power strips) into the Kill-A-Watt power meter. I got 7W total. On average it is 0.5W per an idling power supply. Seven Watts over a year comes as 60kWh/year. With average household consumption of about 6,000 kWh/year (Canada and US uses 11,000 kW/yr), this 15 power supplies constitute about 1% of the entire household consumption.

Now consider that industrial production and consumption of electricity exceeds household consumption 20X, regulation of standby efficiency of external PS in households will affect 0.05% of overall energy consumption.

But of course it would be nice if manufacturers would be forced to state the idle power of their products on a label.

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No brother. if you disconnect your cable then circuit is break , so electron can't pass and there is no any draining of power if device is disconnect.

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