Nexus 7: Won't Charge Through USB Port While Power is On

[jjhoneck]

Re: Won't Charge Through USB Port While Power is On

what is wireless charging? im charging my nexus 7 2nd gen through usb cable hmmmmm

I use this to charge my Nexus 7 (2013). It works great!

Koolpad Qi Wireless Charger Pad for All Qi Compatible Devices Including Samsung Phones with Receivers (White)
Fonesalesman
List Price $49.99
Price $37.99

http://www.amazon.com/dp/B00DQCUVPI...ag=hawk-future-20&ascsubtag=UUacUvbUpU3093793

 

[tflash]

Re: Won't Charge Through USB Port While Power is On

The problem is that the Nexus is using more power while it's on than it's getting from your USB charger. This is a VERY common problem with most USB chargers (unless you use the factory one).

By design, a computer's USB 2.0 port will provide 500ma (milli amps) of power. Tablets, which usually need more than 500ma to charge, will only draw up to 500ma if they "sense" they are plugged into a computer (so it won't damage your computer). The way they sense this is by "seeing" if the two middle prongs of the charger are shorted or not. Most of the cigarette lighter chargers don't short the two middle pins of the USB, so your tablet *thinks* it's plugged into a computer and won't draw more power than 500ma.

You need a specific type of cigarette lighter adapter that has the two middle pins shorted and can supply more power (typically 1.5amps) in order for you to both use your tablet and have it charge at the same time.

The reason most chargers don't short the two middle pins of the USB is because they also work with Apple products. Apple uses a different method where the two middle pins can't be shorted. So if you see a charger that says it's made for both iPads and Android devices, it will only supply up to 500ma to your Android device, even if it says it's rated at a much higher output. You need one specifically for an Android.

Many people will modify their cigarette lighter adapters by opening them up and shorting the two middle pins and only use it with an Android device.

Hope this helps!

"500ma (milli amps) of power" This should say 500mA of current at 5V for 2.5 Watts or 2500mW of POWER.
If you try and 'draw' more current than 500mA at 5V with a power supply that can supply only 2500mW of power, then the voltage will drop below 5V so the V x I (current) will still equal the max output of 2500mW. Forcing the USB port voltage to drop might damage it, but I would hope they are designed to prevent damage in this way.

I have a car/wall combo charger that was made for only apple devices. It came with the 30pin Ipod cable. It is rated to output 2.1Amps of current at 5V. The data pins have low resistance between them, but they are not 'shorted'. When I plug it into the N7 while in the car, it shows as 'AC plugged' and a battery app shows it charging at 1200mA.
When I plug it into the PC USB port, it says 'USB plugged' and charges at about 300mA (while N7 turned on).

I'm glad I don't have to open my charger made for Apple devices and short the data pins for it to charge as an 'AC charger' while in the car.

I don't think this is the OP's problem though, because he said the lightning bolt symbol isn't always on.
If he was just using more power than was being put in, the charge symbol would still be on.

 

[Mjs42]

Re: Won't Charge Through USB Port While Power is On

I have this same exact problem. I've had this Samsung tablet since October 2013 and it always allowed me to read or play on it while charging it on my laptop USB port. All of a sudden in the last week or so it won't allow me to do this anymore. The cord still charges just fine with using the house plug in adapter and it will charge on the USB from the laptop but it will no longer allow me to use the tablet while its charging. I really dislike this because the charge does not last all day while in use.
MJS

 

[George Stevens]

Re: Won't Charge Through USB Port While Power is On

"The unit does not indicate charging (the little lightning bolt over the battery) reliably when plugged in and powered on in the plane."


Often mine does not indicate charging either - but yet it is charging - you can tell by the batter numbers going higher

see my thread

http://forums.androidcentral.com/google-nexus-7-tablet-2013/347005-battery-not-charging.html

 

[Lothsahn]

I had this problem with my Nexus 7 (2013). In my case, the usb charging port on the tablet was severely damaged. This caused the USB port wires to short with each other. USB charging was obviously not possible. However, Tthe unit would charge with the wireless charger--but only when off.

Since I had a wireless charger, and the USB port was destroyed already, I took a hemostat clamp and physically snapped and removed the USB charging port and wires. Once the USB wires were no longer shorting, the wireless charging worked flawlessly.

If you don't care about USB charging or connectivity, this workaround may work for you. Otherwise, you may consider a daughterboard replacement or replacing the USB port.

https://www.ifixit.com/Guide/Nexus+7+2nd+Generation+Micro+USB-Daughterboard+Replacement/36930

Hope this helps someone...