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I am looking for a laptop charger that requires no power outlet but instead utilizes a usb port of another computer to charge my laptop. That is, I am seeking a usb-to-laptop port charger, NOT power outlet-to-laptop's usb charger. Is such a product even possible? I am guessing no since the usb port would not be able to supply enough electricity to power the laptop, even to maintain the battery (not charge it).

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IIRC, you can tricklecharge the new HP chromebook off a USB port. It does come with a specific, high current charger for proper use though –  Journeyman Geek Oct 28 '13 at 2:41
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3 Answers

Converting 5 Volts to 18 (or 24, or...) Volts is quite possible, but to pull 65 watts (much less 85, much less adding conversion losses) from USB's 5 volts would require getting 13 Amperes (current) from the USB port, and THAT you won't find anytime soon, if ever. Some of the high-current special jobs go to 2 Amps (10Watts @ 5Volts), stock is 500 mA (2.5 W) direct-connect, 100 mA (500mW) from older keyboards or unpowered hubs.

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You are correct in the last part - a USB port will never output enough power to get a laptop going. Most laptops are around 18 volts, and the maximum a USB port will put out is 5 volts. An average laptop is around 18 volts (65 watts or so) and upwards from there. (Mine is 85 actually).

tl;dr version: No.

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"around 18 volts of power" -- Volts are not a measure of power. Watts are a measure of power. Volts measure electromotive force. Force is not the same as power (in physics). –  sawdust Oct 28 '13 at 2:07
    
@sawdust fixed it to make it a bit more scientifically correct –  Simon Sheehan Oct 28 '13 at 23:38
    
This answer is out of date. USB 3.1 can produce up to 100W and will be a new standard for DC power in a household. The HP Chromebook 11 is powered by USB. en.wikipedia.org/wiki/USB#USB_3.1 –  benmcdonald Nov 20 '13 at 0:48
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It is not practical, but the voltage conversion would work but would have so few milli-amps that it would not charge. It might extended the life span by 10-30min if the laptop was super low power.

Watch for USB 3.1 I recently read an article. New USB specs 3.1

According to several articles 3.1 provides up to 100 watts of power. You could charge a laptop slooowly with that much power.

100w @ 5v is roughly 25w @20v

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no, 100W at 5V is roughly 85-95 W at 20V depending on how good the guy making the dc-dc converter is. –  Ecnerwal Oct 28 '13 at 2:17
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