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I hope this isn't too confusing. I'm travelling on Ethiopian Airlines in a few days and I see that the flight has a USB.

I know that I can charge my electronic devices however the most important thing for me is using my laptop which has a short battery life. I can't charge it with a USB so I was wondering whether I can connect my laptop charger on the plane to a UK socket adapter that is plugged to the usb port on the ports at the back of the seats.

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    You should link to details of the USB connection offered, does it specifically indicate enough power draw to charge laptops? They're usually meant for cell phone charging. – Alok Aug 20 '17 at 19:20
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    USB Ports are typically 500mA at 5V, thus 2.5W. More powerful ones are becoming prevalent, which may go up to 4A at 5V (20W). Even the most power efficiently laptop's charger would be significantly more. For example, the 12" MacBook has a 29W charger. That's without even accounting for the loss in conversion from 5V DC to the 240V AC that the charger expects – Alexander Aug 21 '17 at 0:50
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    @Alexander's right - even a chromebook (about the lowest power draw that can still be called a laptop) draws 20W+. – Chris H Aug 21 '17 at 8:29
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    Check if you can buy a spare battery for your laptop, perhaps one with more capacity. – Dmitry Grigoryev Aug 21 '17 at 9:32
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    @DmitryGrigoryev got there first. Your battery is either worn out, or was never very good in the first place. Whatever else you buy is just a sticking plaster over the real problem, which is a dead battery. Buy a new battery. And while you're at it, buy a second one as a spare. – Graham Aug 21 '17 at 9:57
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There is no such device because what you are proposing is impractical.

Laptop chargers require between 100 and 240 volts alternating current input. (Some may require a more limited range). USB sockets give 5V direct current, not anywhere near enough to charge a laptop, and the wrong type.

Building a device that could convert 5V DC to the range of AC required would be theoretically posible, but the losses in the system mean it would take much more than the current that is the max a USB can deliver.

You would almost certainly be prevented from connecting the device to the USB in the unlikely event that you made this device, and any attempt to do this might damage the USB outlet.

There are other devices that allow you to extend the life of a laptop batteries. The most common is the laptop power pack, which essentially charges your laptop from a portable battery. This would be a much simpler and acceptable solution.

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    Comments are not for extended discussion; this conversation has been moved to chat. – JoErNanO Aug 21 '17 at 15:13
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    uhm… such device definitely exists and I've linked to hundreds of them on amazon in my answer. As for converting DC to AC I don't think that's necessary. Laptop takes in its 19V in form of direct current, so that's a weird unnecessary step, if you try to do it that way. I don't know where this AC/DC conversion idea comes from but it's bad. – user1306322 Aug 21 '17 at 17:54
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    The problem is not the voltage, voltage can be converted at about 90% efficiency without problem. The actual issue is the fact that USB socket provides 5W max, while typical laptop charger requires around 50W. – Agent_L Aug 22 '17 at 10:45
  • The discussion that was removed (see comment at the top) was exactly this kind of discussion. Please don't continue it. – DJClayworth Aug 22 '17 at 14:21
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    @DJClayworth The fact that others have already pointed out that your answer is misleading means that you need to edit it or remove it, pronto, not that you get to censor further discussion of why it's wrong. – E.P. Aug 23 '17 at 3:17
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Laptops take too much power

It's perfectly reasonable to think that would work. The problem is the laptop class of machines just take more power than readily available present-day USB plugs can possibly serve - 5 or 10 watts depending on vintage and quality.

An iPad will use the full 10 watts and then some when at full screen brightness playing a game - and that's just a tablet.

That said, airlines know you want to plug in, and provide options. Some airlines provide mains receptacles at the seat. This is the new trend.

Some others may have EmPower's obsolete 15V system, which is a special, round plug, good for 75 watts (will cover most laptops). It is electrically similar to an automobile's "cigarette lighter" power port (12-14 volts). Quite a few products were designed for EmPower's 15V system, including cigarette lighter adapters, Apple MagSafe cables), and inverters with Empower 15V plugs and provide mains voltage.

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    @Bergi I know, but vehicle electronics are notorious for lagging 5+ years behind the bleeding edge. Consider yourself lucky if a vehicle plug supports the 10 watt standard. Especially for aircraft where elaborate airworthiness testing is necessary. – Harper Aug 20 '17 at 23:44
  • Just a note for future readers: My laptop claims a 19.5V input. So 15V may very well not cover what your laptop needs. Actually check and make sure! – Mehrdad Aug 21 '17 at 0:53
  • According to the linked article about EMpOwer, they state it gives 110V, while you claim it's 15V, could you quote a source for your fact? – Ferrybig Aug 21 '17 at 6:59
  • @Ferrybig the source is right there in the answer- the SeatGuru and Amazon links both reference the 15V DC version of EmPower. There is also a 110V DC version, which is referenced in the Wikipedia link. An editor on Wikipedia for some reason removed all references to the 15V version but it is there if you look in the history: en.wikipedia.org/w/… – Ivan McA Aug 21 '17 at 10:24
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It definitely exists! (just not how you describe it in your question)

A quick look at my laptop's charger shows that it outputs 19V at 2.1A which is 40 watts of power. So for a 5V USB socket to give us 40 watts it would have to do so at a current of 8 amps, which is equivalent to 16 default-power 0.5A USB connections simultaneously.

You could possibly buy enough USB cables and connect to all the outlets together, risking looking like some sort of hacker, or buy lots of USB charger banks and USB cables to solder up some bulky adapter which will probably end up looking like a scary bomb (don't actually do that :D).

Instead, you should really look at the device category specifically designed for this purpose called Laptop power bank.

Here's one example:

You can find them in a variety of supported plug types and capacities. Make sure yours has a capacity within the allowed limit for your airline. The total capacity might include all your mobile devices with all batteries, so get out a calculator and use one of the electric parameter conversion sites.

To fit your question exactly, you can probably find a version of this which charges itself from 5V USB ports.

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    Most airlines limit how many lithium ion batteries you can carry on. So those laptop power banks may not be allowed. – vclaw Aug 20 '17 at 23:26
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    You need to watch the capacity for sure, but you could still take most of them on. The general regulation is up to 100Wh you can take without restriction (20,000mAh @ 5V or 27,000mAh @ 3.7V) and MOST airlines will also let you take up to two 160Wh banks (32,000mAh @ 5V or 43,000 @ 3.7V). It is important that the capacity is clearly marked, and if it isn't specified in Wh they will calculate on the basis of 5V (which is incorrect, but errs on the side of caution). – Ivan McA Aug 21 '17 at 7:30
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    Sorry, I don't believe this answers the question as the request was to adapt the USB to power a laptop. have you worked out how long would you need to have a power bank charging from USB to power, say, 1hrs worth of laptop usage? Push the alternative, fine, but to m y mind it's not what was asked for. – Gwyn Evans Aug 22 '17 at 22:18
  • @GwynEvans It's basically USB to Bank to Laptop, not USB to Adapter to Laptop. The starting and ending points can be the same, if you find the right bank. Normally though, you'd charge up these bricks on the ground, rather than in-flight from USB, but I'm not gonna stop you. The charging rate seems to be within 60%…90% of what you'd get from the socket, depending on the model (60W…90W power output at 110V). There are also overkill models which can output 200W and therefore charge 2 laptops like mine at normal rate simultaneously, but I'm afraid that's above airline restriction capacity :p – user1306322 Aug 22 '17 at 22:54
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Eventually some USB ports will be able to supply up to 100W for just this purpose (USB 3.0 with SS PD logo) however not the ones on current Ethiopian planes most likely.

Check seatguru.com with your flight information to see if there is a mains outlet so you can use your regular charger. In my limited (yet miserable) experience with this airline, probably not in economy on long haul flights. Probably such an outlet will be available in business or first class, but check. Some airlines outfit their aircraft with such outlets at every seat on long haul flights.

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As mentioned by everyone else, a USB to laptop adapter is useless for most laptops; unless you have one of the newer laptops that allow charging using USB-C (for example, the macbook and macbook pro, dell xps 13, etc.)

If you have one of these laptops - you can charge them using any power that supports USB-C devices ... unfortunately seatback USB power doesn't have that fidelity.

Dell sells a powerbank / power adapter for just this kind of situation (here is an Amazon link):

enter image description here

(the silver part is a battery, the black part is a regular wall adapter)

In normal situations, you use this as your regular laptop power supply; and then when traveling you use it as a battery to top-up your laptop.

It is really quite ingenious and one of the many reasons USB-C looks so promising.

Despite being manufactured by Dell, you can use it with most smaller USB-C laptops.

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USB-C Laptop

If your laptop has good support for USB-C you should be able to charge it using a USB cable, without using a big laptop charger.

Some laptops doesn't support charging using USB-C, but that's for another question.

A Black USB Type C Connector

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