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

[jjhoneck]

Here's a strange one. I've been charging my N7 wirelessly for over a month now. We use this unit for navigation while flying, so it's essential that we keep it plugged into ship's power while in-flight.

For whatever reason, yesterday it would not charge via USB while powered up. I know the power cord is functioning normally, because it charged my Samsung S3 just fine.

Here's the weird part: If I turned the N7 off, it WOULD charge.

Any theories? The Nexus 7 simply didn't recognize that there was power at the USB port while it was powered up. I've recently used a dongle with a thumb drive for data storage for the first time. Does that disable charging through the USB port?

Thanks!

 

[jerrykur]

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

What is the rating of the charger you are using? The factory charger is 5v at @2 amps or so. Typical car chargers are .5 amps.

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[patruns]

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

What is the rating of the charger you are using? The factory charger is 5v at @2 amps or so. Typical car chargers are .5 amps.

Posted via Android Central App

The poster is talking about a USB port. What does a charger and/or a car charger have to do with anything?

 

[S-Doo-1965]

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

Because the amperage of the charger is important.

Sent from my Nexus 7 using AC Forums mobile app

 

[Kookas]

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

You use a tablet for navigating a plane? ;o

Anyway, most likely the USB doesn't put out enough power. Tablets have a much larger battery capacity than phones, so they need more power to charge at the same rate. AFAIK it should charge even on USB, but it might be so slow that the tablet doesn't actually consider it charging.

 

[howardv]

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!

 

[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!

Can you quote some sources of this information? I know a lot about electronics (EET and EE degrees) and some of what you said about batteries ect. just doesn't seem right.
Your sources would save me a lot of 'googling'

 

[howardv]

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

Although I love tinkering with electronics, I'm not an expert by any means. I gathered this info from various sources over the years. Here is one that I had bookmarked:

The Basics of USB Battery Charging: A Survival Guide - Tutorial - Maxim

I'm always into learning more, so please correct me if I'm wrong.

 

[asus_usa]

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

It's your USB charger. If you get another one rated a little bit higher, or one made specifically for tablets, than it should be able to charge. As it is right now, it's charging, although at a very rate - not enough for it to sense that it's charging. The tablet does, indeed, use more power than it's getting when it's on, and that would explain why it'll charge when it's off but not when it's on. Howardv is correct.

 

[jjhoneck]

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

Sorry, I should have mentioned that this wired-in, in-aircraft charger puts out the full 2 amps/5 volts needed for the Nexus 7. We've been using this in the plane for six months.

This problem just started happening in the last week or two. The only thing I can think of is some software switch that has the USB port in "data only" mode, or something...

Any theories?

 

[jerrykur]

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

Sorry, I should have mentioned that this wired-in, in-aircraft charger puts out the full 2 amps/5 volts needed for the Nexus 7. We've been using this in the plane for six months.

This problem just started happening in the last week or two. The only thing I can think of is some software switch that has the USB port in "data only" mode, or something...

Any theories?

Two thoughts. First, it still could be the charger. Try swapping it out. Second, do a factory reset on the N7. It will require reloading apps, but that is pretty quick if you to them from the Play Store.

BTW, how are hardwiring in the charger? Did you have to get the avionics shop to do that? On my C340 I wired in a marine band radio and that turned out to be quite expensive.

 

[patruns]

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

Sorry, I should have mentioned that this wired-in, in-aircraft charger puts out the full 2 amps/5 volts needed for the Nexus 7. We've been using this in the plane for six months.

This problem just started happening in the last week or two. The only thing I can think of is some software switch that has the USB port in "data only" mode, or something...

Any theories?

6 months? Exactly which Nexus 7 are you talking about?

 

[jjhoneck]

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

6 months? Exactly which Nexus 7 are you talking about?

Both the 2012 and (now) 2013 versions.

The 2012 version still charges fine in the plane, so this must be a setting...or glitch...in the 2013 version...

 

[jjhoneck]

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

BTW, how are hardwiring in the charger? Did you have to get the avionics shop to do that? On my C340 I wired in a marine band radio and that turned out to be quite expensive.

Ah, the joys of owning an experimental aircraft! After 20 years of enduring that certificated rigamarole, where you can't even wire in a tablet (!) legally, I can now do just about anything to our RV-8.

BTW: Here's what you need to buy to install in any vehicle. Two wires, and you are done!

Hardwire Barewire Power Micro USB Cable for SmartPhones including Droid and Many Micro USB Devices
MFX2

Price $18.95

http://www.amazon.com/dp/B005J4OTUO...ag=hawk-future-20&ascsubtag=UUacUvbUpU3090553

 

[patruns]

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

Both the 2012 and (now) 2013 versions.

The 2012 version still charges fine in the plane, so this must be a setting...or glitch...in the 2013 version...

That tells us a lot more than your original post. Will it charge wirelessly while turned on? If not, did it used to?

 

[howardv]

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

Both the 2012 and (now) 2013 versions.

The 2012 version still charges fine in the plane, so this must be a setting...or glitch...in the 2013 version...

My 2013 charges awfully slow (if at all) when plugged into it's own factory home charger when it's in use. Possibly the much higher resolution screen could take a lot more amperage than it's predecessor. The unit charges a lot faster if I shut if off and let it sit there.

 

[jjhoneck]

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

That tells us a lot more than your original post. Will it charge wirelessly while turned on? If not, did it used to?

Yes. Wireless charging works fine at all times.

 

[jjhoneck]

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

My 2013 charges awfully slow (if at all) when plugged into it's own factory home charger when it's in use. Possibly the much higher resolution screen could take a lot more amperage than it's predecessor. The unit charges a lot faster if I shut if off and let it sit there.

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

The unit DOES indicate charging (the animated battery) if I turn the unit OFF while plugged in the plane.

 

[Atiya]

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

 

[jerrykur]

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.

The unit DOES indicate charging (the animated battery) if I turn the unit OFF while plugged in the plane.

Does it charge via usb when plugged in with the factory charger.

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