darxus: (June 2012)
darxus ([personal profile] darxus) wrote2013-07-25 09:42 pm
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Charging modern phones is complicated

USB standard power is 0.5 amps x 5 volts = 2.5 watts. That's what you get when you plug into any computer, or an old car USB power adapter.

With that much power, trying to use my phone for GPS navigation results in draining the battery.

The wall plug that came with my Samsung Galaxy S 4 says 2 amps x 5 volts = 10 watts. To signal a device can pull this much power, Apple uses some non-standard set of resistors, and everybody else shorts the data pins together (which is apparently pretty easy with a soldering iron, or by modifying a USB cable). If a phone doesn't notice this sort of indicator, it assumes it's plugged into a computer which would be damaged if it pulled more than 0.5 amps, so it only pulls 0.5 amps.

So basically, you can't just plug a phone into a computer anymore and expect useful charging. I hope they manage to sort this out soon.

I ordered one of these for my car, for $8, after reading lots of reviews (particularly by K. Crawford):
It has one jack for Apple, and one for everything else. Using the wrong jack will still get you at least 0.5 amps.

Samsung sells one, with a single USB jack, for $35.

Nobody makes one with more than one high amp non-Apple jack.

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