When it's plugged in, go into Settings | Battery and see what it says up top. If it says "Charging (AC)", you are good-to-go! If it says "Charging (USB)", read-on.
To differentiate between a USB port on a computer (capable of supplying 500mA unless a higher current draw is negotiated through USB communications) and a wall or car charger that has a USB port, a new specification is used. If the two middle pins of the USB port (D+ and D-) are shorted together (anything <200 Ohms), the phone will know that it's not a computer USB port and will draw the maximum power it can. If those pins are NOT shorted, it will only draw 500mA - which as many of you have discovered, is not enough current to supply a charge while the device is being used. If you turn the screen on, it will barely maintain. If you are Navigating in a car, the battery will actually drain!
When you are looking at a charger, you need to look for two things:
1). That the current it can supply is at least 1A (1000mA). 500mA is not enough. You might be able to get away with 700-850mA, but you may as well just go with 1A.
2). That the two middle pins are shorted together! You could have a 20A charger and your phone will still only draw 500mA off it if those middle pins aren't shorted! To test it, you can use a multimeter in continuity or resistance mode (make sure to unplug it first), or you can just plug your phone in to test what mode it charges in. "Charging (USB)"==BAD, "Charging (AC)"==GOOD
I don't know of any marketing names or specific products that will or won't have those pins properly bridged. My Samsung and Droid wall chargers both had the pins properly bridged, but none of my other wall or car chargers did. I modified two car chargers already to short D- and D+, and they are working great now. I posted another thread about a week ago listing the two specific car chargers that I modded - they are both easy to disassemble, modify, and reassemble.
http://www.droidforums.net/forum/galaxy-nexus-general-discussions/190328-car-charging-issues-solved-hw-hack.html#post1937165
Additional Information:
http://bec-systems.com/site/800/how-do-modern-usb-chargers-work
http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slua551&fileType=pdf
http://www.maxim-ic.com/app-notes/index.mvp/id/4803
https://www.google.com/search?q=D++D-+shorted+USB+charging
To differentiate between a USB port on a computer (capable of supplying 500mA unless a higher current draw is negotiated through USB communications) and a wall or car charger that has a USB port, a new specification is used. If the two middle pins of the USB port (D+ and D-) are shorted together (anything <200 Ohms), the phone will know that it's not a computer USB port and will draw the maximum power it can. If those pins are NOT shorted, it will only draw 500mA - which as many of you have discovered, is not enough current to supply a charge while the device is being used. If you turn the screen on, it will barely maintain. If you are Navigating in a car, the battery will actually drain!
When you are looking at a charger, you need to look for two things:
1). That the current it can supply is at least 1A (1000mA). 500mA is not enough. You might be able to get away with 700-850mA, but you may as well just go with 1A.
2). That the two middle pins are shorted together! You could have a 20A charger and your phone will still only draw 500mA off it if those middle pins aren't shorted! To test it, you can use a multimeter in continuity or resistance mode (make sure to unplug it first), or you can just plug your phone in to test what mode it charges in. "Charging (USB)"==BAD, "Charging (AC)"==GOOD
I don't know of any marketing names or specific products that will or won't have those pins properly bridged. My Samsung and Droid wall chargers both had the pins properly bridged, but none of my other wall or car chargers did. I modified two car chargers already to short D- and D+, and they are working great now. I posted another thread about a week ago listing the two specific car chargers that I modded - they are both easy to disassemble, modify, and reassemble.
http://www.droidforums.net/forum/galaxy-nexus-general-discussions/190328-car-charging-issues-solved-hw-hack.html#post1937165
Additional Information:
http://bec-systems.com/site/800/how-do-modern-usb-chargers-work
http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slua551&fileType=pdf
http://www.maxim-ic.com/app-notes/index.mvp/id/4803
https://www.google.com/search?q=D++D-+shorted+USB+charging
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