When are iMac USB ports powered

Discussion in 'Mac Basics and Help' started by g-boac, Dec 21, 2008.

  1. g-boac macrumors 6502

    Oct 7, 2007
    I occasionally have trouble charging my iPhone via my iMac USB ports. I plug in the iPhone, the screen indicators change to show that the phone is charging (green battery indicator and the lightning bolt symbol). However, when I come back to the phone several hours later, the charge indicator hasn't advanced any. For example, if the indicator showed half-full when I plugged it in, it remains half-full.

    The iMac does go to sleep a few minutes after I leave it, but sleep has never precluded an iPhone battery charge on my MacBook, and most of the time it works on the iMac.

    Is there anything, besides shutting down a computer, that causes a USB port to unpower while the iMac is sleeping? Does it matter whether I am logged in or simply at the login screen?

  2. hughvane macrumors 6502


    Aug 25, 2008
    Banks Peninsula, New Zealand
    USB ports are hardware powered so they operate almost from the moment your iMac is switched on, AFAIK, sleep does not disable a USB port.

    However, to cover that base, check your SysPref > Energy Saver settings to see when you have 'put the computer to sleep' enabled. Maybe you need to adjust that, extend the time to whatever it takes to charge the phone battery.

    Some questions:
    1. When your phone is plugged in for charging, what does Disk Utility show?
    2. Do any other devices 'misbehave' when plugged into the USB port?
    3. Do you use the same USB port for battery charging each time?
    4. Do you have a mains-powered USB hub?
    5. Do you successfully charge your phone battery via other means?
  3. g-boac thread starter macrumors 6502

    Oct 7, 2007
    USB Port Power Status

    Here's what I found out - if you plug the iPhone into a Mac USB port while logged in and while the Mac is awake, OS X sets a bit that tells the Mac something is plugged in and charging. If the Mac then goes to sleep, the port will remain powered, and the iPhone will continue charging.

    If you plug the iPhone into a Mac USB port while the Mac is sleeping (regardless of whether you are logged in), the Mac will wake up and begin powering/charging the iPhone. However, when the Mac goes back to sleep, the USB port will unpower. Apparently the Mac must be awake prior to plugging the iPhone in for it reconfigure its USB port power status so that a specific port remains powered while sleeping.

    if you plug the iPhone in while the Mac is on the log-in screen, the USB port will always power off when the Mac goes to sleep, although the Mac will charge the iPhone while awake.

    Hardware configuration:
    iPhone - iPhone classic/8GB, firmware 2.2
    computer - iMac 20"; 2GHz Intel Core 2 Duo; Boot ROM Version IM71.007A.B03; Leopard 10.5.5

  4. BlueRevolution macrumors 603


    Jul 26, 2004
    Montreal, QC
    Huh, that's really odd. Well, I guess you've answered your own question. :) Are you sure than the iPhone will continue charging after the iMac goes to sleep, though? It could just be incorrectly indicating that that is the case.

    I will add that I find it really annoying how connecting (or disconnecting!) a USB device will be enough to wake my computer from sleep. I usually leave my iPod charging and my Mac sleeping overnight, then grab my iPod in the morning before I leave and have to put my Mac to sleep again.

    If you use a powered USB hub, the power will usually remain on even when the USB connection is removed.
  5. chinarut macrumors member

    Nov 14, 2005
    hmm - i the behavior I am experiencing on my iMac is not the same :(

    for over 4 months, it was never "conditional" - the USB port off my keyboard was always powered whether or not my iMac was awake or sleeping.

    ever since I started fiddling around with switching the USB port the keyboard was plugged into and a USB hub, the port off my keyboard hasn't been powered while sleeping.

    I've tried rebooting while my iPhone is and isn't plugged in and plugging in my iPhone while it is awake like you suggested with no luck.

    If anyone can chime in and let us know how I can reliably have the USB port off my keyboard powered while sleeping like it was before, this would be great!
  6. petermcphee macrumors 6502a


    Aug 20, 2008
    It is possibly a problem with the keyboard. I charge my phone from my iMac's keyboard USB port overnight when the computer is sleeping (due to inactivity) and I have never had a problem with the port lacking power.
  7. chinarut macrumors member

    Nov 14, 2005
    thanks peter! you're absolutely right - i tried to plug my iPhone directly to one of the 3 USB ports in the back of the iMac and it stays powered even when i put the iMac to sleep.

    do you think my keyboard is now defective or is there something else I can do to restore its previous behavior? i ask cuz it's not like the port just suddenly died - it's now conditional and dependent on the state of the iMac sleeping or not - doesn't really sound like a defect esp based on previous posts in this thread.

    ps. i tried to swap USB ports for kicks but same behavior...
  8. megastuff999 macrumors member

    Feb 13, 2008
    Sorry to drag this one back from the dead, but did you ever fix this issue? I have exactly the same problem on my 2.8GHz 2008 model iMac. Plug iPhone into one of the three USB at the back and it continues to charge while sleeping.

    Run it off the aliminium keyboard and it doesn't. However, it always used to...?
  9. chinarut macrumors member

    Nov 14, 2005
    hey - thanks for the ping - your timing of your post is uncanny actually :rolleyes:

    I'm definitely going to call AppleCare and ask them about my keyboard.

    what I've been doing since i last posted is plugging my iphone in a 4-way USB hub (no external power) - it worked pretty well for a few weeks.

    however, last nite, I found the port I usually use unpowered - I woke my iMac up and plugged by iPhone in before putting it back to sleep and this worked.

    don't know if this helps but i'll let ya know if i get my keyboard port powered again while my iMac sleeps!

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