USB Port Over Powered??

Discussion in 'MacBook' started by Shadoh, Mar 19, 2009.

  1. Shadoh macrumors newbie

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    Mar 19, 2009
    #1
    Hello everyone, I am new to this board.

    I recently got a Macbook and have a iPhone and iPod shuffle. The thing is there isnt enough usb ports on the Macbook so i had to get a hub.

    The hub i got IS self powered and does not require a external power adapter. My concern is that I am withdrawing too much power from my usb port through this hub.

    It is a 4 port hub and a External HDD ( has own power supply), Optical mouse is connected to it. also I charge my iPhone and shuffle via the same hub. I am afraid that there is power limit feature and it will fry my computer.

    I notice if i boot in boot camp to windows. Windows will display a error message telling me, I am not allowed to have this many device drawing this much power.....

    Anyone know if I should be okay as long as OS X doesnt give me a message or should i really consider getting a USB hub with its own power adaptor? Thanks. :)
     
  2. shady825 macrumors 68000

    shady825

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    #2
    You can have up to 127 USB devices plugged in.
    CNET
     
  3. NewMacbookPlz macrumors 68040

    NewMacbookPlz

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    Sep 28, 2008
    #3
    The hub is just drawing current from the USB port it's plugged into. The windows message is because all the devices are probably maxxing out the port, so some are dialing their power draw down to maintain USB-port spec compliance.
     
  4. shady825 macrumors 68000

    shady825

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    #4
    Yea thats a problem on the Windows side of things.
    I've read that the externally powered hubs resolve that problem. "a USB device can request up to 500mA, but a non-powered hub can only supply 400mA to be shared between four devices. Using powered hubs usually avoids problems. USB devices don't speak unless spoken to, so it shouldn't matter how many you have connected but idle, as long as each one has its own 7-bit address."
     
  5. Shadoh thread starter macrumors newbie

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    Mar 19, 2009
    #5
    okay so does it all comes down to as long as OS X doesn't display any error message and I can still power all my devices and charge my iPhone OR shuffle at the same time, should I not worry too much?
     
  6. shady825 macrumors 68000

    shady825

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    #6
    Did you not read what I posted? you can have 127 devices. So NO you 'shouldnt worry'
     
  7. Shadoh thread starter macrumors newbie

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    #7
    Yes I did read it and thank you for the reply. But my main concern is more about the POWER being pulled out of the USB port from the hub connecting all these things.
     
  8. shady825 macrumors 68000

    shady825

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    #8
    I dont think you read what I posted AND the links I gave if you are still asking this question.
     
  9. shady825 macrumors 68000

    shady825

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  10. NewMacbookPlz macrumors 68040

    NewMacbookPlz

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    Sep 28, 2008
    #10
    A USB port can only supply an upper limit of 500mA of current. No matter how many devices you have plugged in, you cannot pull more power than that. The devices are designed to scale back their power consumption to accommodate this limitation

    The only exception I can think of at the moment would be the specially setup USB port on the MBA, which sends more current to power the external SuperDrive.
     
  11. Sun Baked macrumors G5

    Sun Baked

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    May 19, 2002
    #11
    If the device draws more than it reports, OS X shuts the port down.

    If the devices reporting on the port add up to needing more than the port can deliver, it shuts the port down.

    Something that tends to happen with large bus powered drives, which switching to a powered hub solves.

    ---

    Basically, if the OS is letting things work, don't worry about it.
     
  12. Shadoh thread starter macrumors newbie

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    Mar 19, 2009
    #12
    Oh okay. So the port won't even allow more than 500mah. The USB devices power down themselves to share power. Well that's all I wanted to know. Thanks
     

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