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    Default Getting extra operating current power from MacBook Pro for Nexus 4

    My apologies, I couldn't find any posts referencing what I needed, but please point me in the right direction if one exists. Basically, I want to charge my Nexus 4 faster using my MacBook Pro (and my old ThinkPad at work, too), if I can. I found this article: That references how my USB ports on my MacBook pro provide "extra operating current" for approved Apple peripherals. While that would get me to 1 amp (not 1.2 as on my Nexus 4 wall charger), that would be better than the 500mA that it provides right now. I know the ports support this, I tested them with my old iPhone and iPad.

    So my basic question is this: Is there a trick/hack/tweak that can get my USB ports to output the 500mA extra operating current when my Nexus 4 is plugged in.

    Follow up: Is there a way in Widows XP on a Lenovo ThinkPad T61 to tell what power the USB ports are putting out? I don't think they ever charged my iPhone very quickly, so I'm guessing 500mA is all I'll get, but I wanted to check.

    Love my first Android phone so far, just need a little more juice. Thanks!
  2. #2  

    Default Re: Getting extra operating current power from MacBook Pro for Nexus 4

    The section labeled "Power" in this Wikipedia article details the standards for power availability on USB ports. I found this of particular interest:

    The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V5%) between the positive and negative bus power lines. For USB 3.0, the voltage supplied by low-powered hub ports is 4.455.25 V.

    A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. A low-power device draws at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. A high-power device draws at most the maximum number of unit loads permitted by the standard. Every device functions initially as low-power but the device may request high-power and will get it if the power is available on the providing bus.

    Some devices, such as high-speed external disk drives, require more than 500 mA of current and therefore may have power issues if powered from just one USB 2.0 port: erratic function, failure to function, or overloading/damaging the port. Such devices may come with an external power source or a Y-shaped cable that has two USB connectors (one for power+data, the other for power only) to be plugged into a computer. With such a cable, a device can draw power from two USB ports simultaneously.
    Hmmm... With such a Y cable, could you charge your N4 twice as fast? Would you dare to try it?
  3. #3  
    Citizen Coyote's Avatar

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    Default Re: Getting extra operating current power from MacBook Pro for Nexus 4

    Quote Originally Posted by N4Newbie View Post
    Hmmm... With such a Y cable, could you charge your N4 twice as fast? Would you dare to try it?
    Probably wouldn't hurt it, as I imaging the phone would only draw as much power as it could handle. That's assuming it worked in the first place. But why not just use a wall charger?
  4. #4  
    natehoy's Avatar

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    Default Re: Getting extra operating current power from MacBook Pro for Nexus 4

    Quote Originally Posted by N4Newbie View Post
    The section labeled "Power" in this Wikipedia article details the standards for power availability on USB ports. I found this of particular interest:

    "Such devices may come with an external power source or a Y-shaped cable that has two USB connectors (one for power+data, the other for power only) to be plugged into a computer. With such a cable, a device can draw power from two USB ports simultaneously."

    Hmmm... With such a Y cable, could you charge your N4 twice as fast? Would you dare to try it?
    I don't believe so. Such devices treat the two cables as separate power sources and have a driver to request 5 or 6 loads from each of the two separate USB ports. Shortwiring two USB ports and sending a signal over each simultaneously would, at best, not work. At worst, you'd be releasing some of the magic smoke.

    The problem with being able to request this additional power is that you need a device driver so the host computer can recognize the request. "Approved Apple Devices" means those for whom Apple has written a driver and installed it on MacOS so the devices are recognized. I'm not sure if Google has a MacOS driver for the Nexus 7, but if you could find and install that driver on your Mac, the Nexus 4's request to go to high-power mode could be heard and understood, and the Mac could up the amperage on the port.

    For the older Thinkpad, it may be possible to simply get a charging cable (data pins shorted). Most computers see shorted data pins as a request for higher-rate charging, and if they have a port capable of providing more power they will. I don't know if the Mac would also recognize this - I believe it uses a driver and a specific request (in software) from the device being charged.
  5. #5  

    Default Re: Getting extra operating current power from MacBook Pro for Nexus 4

    Quote Originally Posted by Citizen Coyote View Post
    Probably wouldn't hurt it, as I imaging the phone would only draw as much power as it could handle. That's assuming it worked in the first place. But why not just use a wall charger?
    Agreed, but the original poster was inquiring specifically about being able to charge from his MacBook Pro's USB ports.

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