30
3
Possible Duplicate:
Charge a laptop via USB power (500mA)?
I will fly to China in the next month which will take a mammoth 18 hour flight. The plane has USB power source on it.
I know USB only has 5v and 0.5 amps output and laptop is 20v and 3.25amps. So 4 USB's would be short on the amps but supply enough voltage. Is there a transformer out there that could make this set up work?
Jefro
Posted 2011-05-17T13:48:15.250
Reputation: 301
42
First, if you got a transformer, you'd need more than 4 USB ports, as the power draw will be constant at 65W. As each USB provides 2.5W, you'd need at least 26 USB ports, and that's assuming that you have perfect efficiency in your transformer (which you won't). I'm pretty sure the airline won't let you have 26 USB ports. Even if they did, it's unlikely that an airline would let you plug in what would have to be a handmade transformer. And, even if they did, it is almost certain that airport security wouldn't let you through with such a transformer in your bag.
This is pretty much guaranteed to fail. There is a reason we don't power laptops by USB. My suggestion? Get an extra battery or two, and just swap them in and out as needed.
Lukasa
Posted 2011-05-17T13:48:15.250
Reputation: 1 995
31haha... I can see the faces of security now as they open my bag to find a mass of 26 usb cables all wired into a handmade box... – Jefro – 2011-05-17T14:44:30.117
2Or, with 7 parallel blocks of 4 supplies in series you get 20V, 3.5A. This would require 4 * 7 = 28 5V supplies, but does not need the transformer. Not that that is any more feasible... – sblair – 2011-05-17T15:20:38.700
Note that USB ports for power may supply more than 0.5 amps, as ipods/smarthphones may draw more than that if available. My 'droid says "connect to charger, usb port doesn't supply enough power" when I run tethering sometimes. – Macke – 2011-05-17T18:20:07.143
It make me sad to up-vote this... – Trufa – 2011-05-18T00:29:29.293
since those ports are probably "dumb" power supplies, you can most likely draw a lot more power from them. – Martin – 2011-05-20T14:48:53.207
10
Firstly, the power draw will NOT be constant at 65 watts. The maximum rated output of the normal laptop adapter is 65 watts.My laptop adapter is also rated at 65 watts. When not charging the battery, my laptop typically draws between 10 and 25 watts.
If you really have to draw from the USB, I'd do it by charging an intermediary battery and cycling power to the laptop in waves supply power for at least a minute. Depending on your battery chemistry, perhaps start applying power to the laptop at 80% charge and remove power at 40%. Size your intermediary battery accordingly.
You won't be able to reasonably power your laptop fully, but you will be able to power it enough to appreciably increase your run time with the use of four USB ports. (10 watts nominal). Voltage conversion is an exercise for others.
It is likely that those adapters may be "charging" type adapters that put out a full amp at 5 volts. That 5 watts from one port would still be useful and could give you a freshly charged laptop battery if you fell asleep on a long-haul flight.
Jeff Ferland
Posted 2011-05-17T13:48:15.250
Reputation: 823
Personally, I wouldn't risk it, but you're quite right, and I like your solution. +1 for you. – Lukasa – 2011-05-17T16:50:32.800
10
This is going to sound a little silly but it is completely allowed by FAA regulations.
You are allowed to bring in sealed Lead-Acid batteries.
Attach a 12v cigarette adapter to that then hook that up to a small power inverter (you can get laptop ones for fairly cheep). You can then use that to charge your battery in flight.
Here is a DIY video of how to make one.
Scott Chamberlain
Posted 2011-05-17T13:48:15.250
Reputation: 28 923
7As long as the SLA doesn't contain more than 100mL of acid... runs – Ignacio Vazquez-Abrams – 2011-05-17T18:00:21.493
5
Are you sure it's just USB because many planes now have a power connector for laptops - for example:
http://www.engadget.com/2007/07/24/laptop-power-in-flight-internet-coming-to-qantas/
Quite often the airline's Web site will cover their fleet's features so it's worth taking a look - and this site (below) also has lots of useful info:
Linker3000
Posted 2011-05-17T13:48:15.250
Reputation: 25 670
Economy class seats are equipped with USB and Ipod chargers only :(
Well, that settles that then :-( – Linker3000 – 2011-05-17T16:15:55.140
7@Jefro, better upgrade to First Class :P – Kevin Peno – 2011-05-17T16:48:17.237
0
There's absolutely no way you can charge a laptop via USB or a USB docking station. The only way is through the AC adapter or via expansion port/dock.
Diogo
Posted 2011-05-17T13:48:15.250
Reputation: 28 202
8That sounds like a challenge... :P – Richard Marskell - Drackir – 2011-05-17T14:07:45.643
@Drackir - If I had written this I would have qualified it with 'reasonable' haha – Shinrai – 2011-05-17T14:15:54.743
4320V x 3.25A = 65W required. 5V x 0.5A = 2.5W available. 65 / 2.5 = 26 USB outlets needed. – RedGrittyBrick – 2011-05-17T14:06:38.513
@RedGrittyBrick - better pack lots of 10M/20M USB extension leads then. – Linker3000 – 2011-05-17T14:23:19.120
8argh! I'd have to ask 25 other passengers if I can use their USB ports lol – Jefro – 2011-05-17T14:55:45.520
67New device found: Airbus 380. Do you wish to configure the device now? – Simon Richter – 2011-05-17T15:00:32.397
You might want to see the answers to this question as well: http://superuser.com/questions/94170/can-i-charge-a-computer-through-its-usb-port-which-brand-models
– CarlF – 2011-05-17T15:13:19.4574
@Simon Richter: http://www.heise.de/ct/schlagseite/2003/1/gross.jpg
– starblue – 2011-05-17T19:57:49.4971
Since RedGrittyBrick pointed out so quickly that power requirements make this impossible (though you don't really need that much power), this question is probably over-and-done, but I want to clarify: Finding a transformer is not a good question for Electronics. We'd welcome questions about the design of a DC-DC converter, but we're just as adamant (if not more adamant) about prohibiting bad shopping questions as Superuser.
– Kevin Vermeer – 2011-05-17T21:51:52.323When your laptop is idle the USB might have enough power to charge or break even. When you do something high power... USB will not keep your battery charging BUT it is important to note that it will still help you run your halptop longer! – Trevor Boyd Smith – 2011-05-18T02:30:08.720
Related: http://superuser.com/questions/158398/charge-a-laptop-via-usb-power-500ma
– Jay Bazuzi – 2011-05-18T05:13:44.437@RedGrittyBrick 65W is enough for heavy use + charge at the same time. Wouldn't we require less for minimal usage? The user will probably be happy if he could extend his battery life from 6-8 to 16-18 hours. – Daniel Beck – 2011-06-12T16:43:33.003