darxus: (June 2012)
darxus ([personal profile] darxus) wrote2013-07-25 09:42 pm
Entry tags:

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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[identity profile] frobzwiththingz.livejournal.com 2013-07-26 04:16 am (UTC)(link)
.5 amps is merely what the spec *guarantees* you will be able to pull from a compliant USB port.

Many computer USB ports can provide much, much more. The one on the desktop computer i'm typing this at seems to be able to source at least 3 amps.

Edited 2013-07-26 04:16 (UTC)

[identity profile] darxus.livejournal.com 2013-07-26 11:00 am (UTC)(link)
Right, but devices generally don't pull significantly more because of the chance of causing damage, right?

[identity profile] xuth.livejournal.com 2013-07-28 01:01 am (UTC)(link)
But per the original specs, connected hardware is supposed to not draw more than .5 amps either or else you could do bad things. Thus hardware needs to negotiate higher amperages if it needs to draw it and lots of devices precede the standards as they evolve to handle higher current devices. But there are standards for at least 1.5 amp USB ports (http://www.usb.org/developers/devclass_docs/USB_Battery_Charging_1.2.pdf) and devices that draw much more than that.

[identity profile] feng-huang.livejournal.com 2013-07-26 05:42 am (UTC)(link)
Hey, I just got something like that to replace one that wouldn't charge my Nook. (Its documentation says only that it won't charge when connected to a computer, and tells you just to use Nook accessories and chargers.) As it happened, I was rebooting my computer (OS reinstall, long story) and playing around in the BIOS, and I decided to enable the charging and disable the USB functionality of the two yellow ports on my motherboard, and incidentally, now I know why you can't do both at the same time. (It lets you disable high-amp charging mode, enable it when sleeping only, or enable it all the time, but at the cost of disabling the USB functionality on them.) Anyway, the Nook started charging perfectly when I connected it to one of those ports, so I quickly figured out what the issue was. To be honest, I picked the one I did after reading reviews on others saying that the blue LED was bright in the car, and then I saw a couple on this one that said that its light wasn't too bright.

[identity profile] darxus.livejournal.com 2013-07-26 10:59 am (UTC)(link)
It's really cool that you can set that in BIOS, I'll have to check that out.

I also can't believe these things don't use the freaking data connection, when they don't see the shorted pins, to say "Hey, how many amps can I pull?"

[identity profile] feng-huang.livejournal.com 2013-07-26 02:59 pm (UTC)(link)
That's a great idea. And also, regarding your other post about the phone itself, I've resisted upgrading for several years for the same reason, plus the fact that I didn't feel like paying so much more for the data plan and having to track my usage. I think T-Mobile looks pretty good as far as the price and monitoring go. Now I just have to decide whether I distrust Apple or Google more, and then maybe which phone to get, based on what that decision is. (S4 looks great, and that's very useful info about the One.)

[identity profile] darxus.livejournal.com 2013-07-26 11:00 am (UTC)(link)
I did successfully charge my phone overnight off of my computer.

Slower charging is supposed to be healthier, right?

[identity profile] inkedandkinked.livejournal.com 2013-08-08 04:28 am (UTC)(link)
I run a truck stop inverter in my vehicles. It plugs into the cigarette lighter/charger port and produces enough current to run the standard wall charger that came with the phone.

[identity profile] darxus.livejournal.com 2013-08-08 04:36 pm (UTC)(link)
Then I'd have to unplug the wall charger that came with my phone and take it with me constantly. I could also just buy the car charger from the manufacturer for $35. They're just frustrating solutions, when it should all just be standardized.