charger amps

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On Fri, 06 Sep 2013 10:21:41 -0500, The Daring Dufas

USB might be a standard but for chargers everyone has their own twist on the theme. Some USB chargers WILL NOT work with some appliances. Some will assume they're connected to a USB port (.5A) even though the supply is capable of much more. There is a big market in the industry for chips that understand everyone's charging twist (and for those who've figured out how to make this stuff programmable).
That's the nice thing about standards; there are *so* many to choose from. USB is no different (and it's getting worse).
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wrote:

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On Fri, 06 Sep 2013 08:08:58 -0500, The Daring Dufas

all of the cahargers from the crappy 500ma chinese junk to the best 2.5 or 3 amp (usb3 - usually) chargers. Big works on small, but small doesn't work on big. Usually you can get away with the small one to charge something bigger if the something bigger is turned off - but don't count on it.
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On 9/6/2013 12:24 PM, snipped-for-privacy@snyder.on.ca wrote:

OOPS! Looks like one of my eyeballs was looking in the other direction, the one that works. I overlooked USB and thought it was a 2.5mm round plug like the one that's on the 7" tablet I have but it also has a micro USB connection but I don't think it can get power over it. Premature postification, it happens sometimes to all us guys when we get excited. O_o
TDD
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On 9/6/2013 5:23 AM, Frank Thompson wrote:

Yes and no.
The manufacturers do some strange things with the data pins to indicate that the device is capable of charging at.
For the iPhone and iPad, 2.0V on both data pins tells the iPhone to charge at 500mA. 2.8V on D- and 2.0V on D+ tells the iPhone to charge at 1000mA. 2.0V on D- and 2.8V on D+ indicates 2000mA and is for the iPad.
This system is designed to prevent polyfuses from opening on chargers and computers. If you plugged an iPad into a computer's USB port, and used a cable that tried to trick the iPad into charging at 2000mA, the port would shut down. At 500mA the iPad will charge (at least if it's turned off; if it's on then it will discharge, but more slowly).
The key thing to remember is that Apple devices will NOT charge just with 5V on USB pin 1 and GND on USB pin 4. They _must_ see a DC voltage on pin 2 (D-) and pin 3 (D+). A Google Nexus 7 tablet (at least the first generation) will NOT charge just with 5V on USB pin 1 and GND on USB pin 4, the data pins must be shorted. This applies only for chargers, not for a computer's USB port.
On my Google Nexus 7, unless I short the data pins together it won't charge at all from a USB charger (it will charge at a slow rate from a computer or at a fast rate from the supplied charger). So I made up a bunch of cables with the data wires shorted so I can use a high-current car charger or high-current wall wart. Of course these cables can't be used for data transfer anymore.
The question is, "what does the Kindle HD do with pins 2 & 3? Does it short them together for high speed charging? Or do they have a scheme similar to Apple's? I could not find any information on what Lab126 did regarding this.
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Huh? Even Google says you can use other chargers. You just have to use the correct amperage or you may get a slow or no charge.
"If you're using a charger rated less than the one that came with your tablet, your tablet may charge very slowly, or may not charge at all."
https://support.google.com/nexus/7/answer/2668668?hl=en
To check I just took 5 random chargers out of the junk drawer and my Nexus 7s (both old and new models) charged from all of them using a generic cable.

You seem to have wasted your time...
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On 9/6/2013 2:06 PM, AL wrote:

No, that's not the way it works. If you plug the Nexus 7 (the original anyway) into a USB port that only supplies +5V and ground it will not charge at all. If you short the data pins together it charges at maximum current (shows up like an AC charger). If you plug it into the USB port of a computer it will charge at 500mA.

Nope. Without those cables the tablet would not charge at all. I had some 2.1A car chargers and wondered why they didn't work at all. Once I used a cable with shorted data pins it all worked fine.
What did happen is that with Android 4.2 there is no longer a need for the special cables. But I am running 4.1 (ICS) because there are apps that won't work on 4.2 (JB).
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Of course that's the way it works. *I repeat myself*: Google says so and I just checked it out with a bunch of my old generic chargers on my own 2 Nexus 7s (original and current model) and they *do* charge.
Heck even my iPad and iPhones charge on generic chargers. Now that would be a switch if Apple stuff could use a generic charger and Google tablets went proprietary and couldn't... 8-O

As long as I use the correct size generic charger, both models charge at max.

Aha!!! Say that again. "no longer a need for the special cables". Thank you. Boy that took awhile to come out, huh... ;)

So I guess that instead of posting this misleading statement:

You really meant to post:
On *my own personal Nexus 7* I chose to remain with an obsolete version of the OS in order to run some old apps and for this reason *I* can't use a generic charger on *my* Nexus 7.
But for those who don't have a Nexus 7 and might be thinking of getting one, Google has long since updated all (2012 and 2013 models) to Android 4.3 and they will work just fine on a generic charger of the correct size... no cable hacking required.
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