Re: Charging USB devices with Fedora

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On Fri, 2010-03-19 at 10:22 -0400, ka1ifq wrote:
> Does the cable you are using have all 4 wires? Some cables are made
> for data xfer only. try using the cable you have with a usb charger
> and see if it works. I had a similar problem with a phone and it was
> the cable I was using.

USB cables have four wires and a shield.  Two of those wires are used
for power, two for data.  I've *NEVER* seen a cable that only has data
wires, and it would be a seriously bad idea to attempt it.  The shield
isn't a data ground, and shouldn't be used that way.  And there's ZERO
way that such a cable could be used to power/charge anything.

On the other hand, there are cables that are power-only, which don't
carry the data wires.  And these can be used, though will only be
reliable with low power devices.

Some power-only cables short the data pins together at the plug, and
that's used as a way to tell *some* USB hosts to supply high current to
the socket (only a newish host would support doing this).  A more sane
solution would be for them to put a small USB chip in the plug that
properly negotiates high power modes from any USB host.

Various device, such as some hard drives, come with a cable that plugs
into two USB ports at the same time.  If they're so badly built that
they simply short the power lines together from two USB sockets, as some
are said to do, then you stand a really good chance of destroying the
host.

-- 
[tim@localhost ~]$ uname -r
2.6.27.25-78.2.56.fc9.i686

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.




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