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Do they make a Motorola RAZR 5-pin USB 2.0 to mini-USB cable?



 
 
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  #11  
Old April 8th 13, 12:21 AM posted to alt.cellular.t-mobile,alt.cellular.tech,sci.electronics.repair,alt.home.repair
SMS
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Default Do they make a Motorola RAZR 5-pin USB 2.0 to mini-USB cable?

On 4/6/2013 4:35 PM, Mark Zenier wrote:
In article , Francis C. wrote:
William Sommerwerck wrote:

I believe the resistor is needed to "clue" the power supply that
something that "wants" to be charged is connected.


I'm confused because I just tested a "normal" cable and this was
my observation:

Motorola RAZR V3 connected to wall-wart USB charger -- fail
Motorola RAZR V3 connected to automotive USB charger -- fail
Motorola RAZR V3 connected directly to Linux PC -- charged!

The weird thing is that I used the same cable for all 3 tests!


USB has power control from the host. The Linux system is going to
interrogate the phone and set up the internal hub/controller to whatever
power level the phone wants.


On a Windows box, the Motorola phone driver isn't built in. It looks
like Linux includes it so you don't need to install Motorola Phone Tools
in order to charge.

But I think you've got it backwards. The USB power controller on the
computer does not allow setting different current levels as requested by
the phone.

What really is happening is that the USB driver is telling the phone
that it's plugged into a USB port and that the phone can charge at
500mA. If you trick the phone into charging at 1.25 amp by using a
resistor in the cable then the over-current protection on the USB port
will probably trip (it doesn't trip at 501mA, more likely to trip at
800-1000mA, but 1250mA is probably going to trip it). If you trick the
phone into charging at 500mA with a resistor then it would work fine.

On my Asus/Google Nexus tablet, if you short the USB data pins then it
thinks it's plugged into a 2.1A charger no matter what it's plugged
into. You need to do this to use a dumb 2.1A to 12V to USB adapter, and
it's part of the USB spec. But it will charge from a Motorola Micro USB
car charger too, just slower.

USB ports were not designed to be used as chargers, but the USB 3.0 spec
has addressed the charging issue pretty well.

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  #12  
Old April 8th 13, 06:08 PM posted to alt.cellular.t-mobile,alt.cellular.tech,sci.electronics.repair,alt.home.repair
Francis C.
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Default Do they make a Motorola RAZR 5-pin USB 2.0 to mini-USB cable?

sms wrote:

USB ports were not designed to be used as chargers, but the USB 3.0 spec
has addressed the charging issue pretty well.


I'm a little confused ...

I have both USB 3.0 and USB 2.0 ports on my Linux laptop.

Should I expect them to work differently with a standard USB-to-mini
cable with the Motorola RAZR V3?



  #13  
Old April 8th 13, 07:07 PM posted to alt.cellular.t-mobile,alt.cellular.tech,sci.electronics.repair,alt.home.repair
SMS
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Posts: 7,841
Default Do they make a Motorola RAZR 5-pin USB 2.0 to mini-USB cable?

On 4/8/2013 9:08 AM, Francis C. wrote:
sms wrote:

USB ports were not designed to be used as chargers, but the USB 3.0 spec
has addressed the charging issue pretty well.


I'm a little confused ...

I have both USB 3.0 and USB 2.0 ports on my Linux laptop.

Should I expect them to work differently with a standard USB-to-mini
cable with the Motorola RAZR V3?


Yes, no, maybe so.

There's no short answer. A USB 3.0 port _could_ provide a higher maximum
current if the computer manufacturer decides to provide the higher
current, but it's not required.

A USB 2.0 port should supply a mininum of 500mA and is technically
required to shut down if the current exceeds 1.25A. A USB 3.0 port
should supply a minimum of 900mA and is supposed to shut down at 1.5A.
But there are also higher power options if communications is not
occurring simultaneously.

The reality is that both the USB 2.0 and 3.0 ports probably are able to
provide 900mA, but this depends on the laptop. For example, I have a
Dell netbook that shuts the USB ports down at about 700mA, but on other
machines I have they'll go well over 1000mA.

I doubt if the USB driver and the phone are smart enough to negotiate to
provide 900mA if the cable is plugged into the higher power port.
Remember, it's the phone that decides how much current to try to draw
from the USB port. The phone manufacturer has to err on the side of
caution and draw only 500mA from the USB 2.0 port even though most USB
2.0 ports could supply more than 500mA.

  #14  
Old April 8th 13, 08:25 PM posted to alt.cellular.t-mobile,alt.cellular.tech,sci.electronics.repair,alt.home.repair
Francis C.
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Posts: 12
Default Do they make a Motorola RAZR 5-pin USB 2.0 to mini-USB cable?

sms wrote:

There's no short answer. A USB 3.0 port _could_ provide a higher maximum
current if the computer manufacturer decides to provide the higher
current, but it's not required.


That explains why when I plugged in the Motorola RAZR V3 into both types
of ports on my Linux laptop, it simply said "Charging" but didn't give
any other indication.

  #15  
Old April 8th 13, 08:26 PM posted to alt.cellular.t-mobile,alt.cellular.tech,sci.electronics.repair,alt.home.repair
William Sommerwerck
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Posts: 8
Default Do they make a Motorola RAZR 5-pin USB 2.0 to mini-USB cable?

A USB 2.0 port should supply a mininum of 500mA and is technically
required to shut down if the current exceeds 1.25A. A USB 3.0 port
should supply a minimum of 900mA and is supposed to shut down
at 1.5A. But there are also higher power options if communications
is not occurring simultaneously.


Overloads at startup will produce error messages, followed by prompts to reset
the ports.

Ports /not/ wired directly to the mainboard can fail to supply even the
nominal spec'd maximum current. I have a USB 3.0 external drive that won't
work with the ports on the front of the machine, but does work with those on
the rear.

 




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