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Re: [OM] Another gadget obsoleted.

Subject: Re: [OM] Another gadget obsoleted.
From: Chris Barker <ftog@xxxxxxxxxxxxxx>
Date: Sat, 5 Jan 2013 06:57:48 +0000
Chuck

No, sorry, I didn't,  only the first few lines in which the author describes 
the bridging of the 2 ports.  Thanks (and to Piers) for enlightening me on the 
existence of such protocols.

They sound like sensible restrictions, rather than sinister.  And I now 
remember that I had USB output to use in the car which did not charge a 
previous iPhone: I was thoroughly confused by that, but no longer :-)

Chris

On 4 Jan 2013, at 23:10, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx> wrote:

> I don't think you read my link.  It discusses an *apparent* proprietary 
> signaling system in 12V/USB chargers that iPads recognize and Androids 
> do not.  A high current charging device such as an iPad or Android 
> tablet needs to be aware of the USB connection and, if it's attached to 
> a computer, throttle itself back to the maximum current draw specified 
> for a USB port on a computer (0.5 amp IIRC).  However, if the charger is 
> simply a USB connector connected to a 12V outlet in a car then the 
> device can safely draw 2 amps or more.  Certain of these 12V chargers 
> will rapidly charge an iPad since the iPad somehow knows there's a high 
> current capacity automobile on the other side of the USB connector.  The 
> Androids typically do not since they don't understand whatever the iPad 
> is doing to realize it's charging from a car rather than your laptop. 
> The recommended charger in the link is one that does allow an Android to 
> draw 2 amps for charging... depending on which of the 2 USB sockets it's 
> connected to.
> 
> There's a lot of detailed engineering study in that link.

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