Charging 3G With Always-On USB

Discussion in 'iPhone' started by ThrillHouseMD, Jul 6, 2009.

  1. ThrillHouseMD macrumors member

    Jul 11, 2008
    In the power options of my Lenovo T61 there is an option to keep power to the USB even when the computer is shutdown/in standby. With the option turned on and the computer off, I plug my iPhone into the USB but see no sign of it charging.

    I'm sure the "Always-ON" port works because it lights up and spins my WD Passport hard drive without a hitch.

    Odd because I would assume if it was a voltage problem the power to spin up the USB hard drive would definitely trump the power it takes to charge the phone.

    Anybody have an idea? Thanks.
  2. cobalt135 macrumors regular

    Dec 28, 2008
    I am gonna say it is either your computer or the sync cable. Does it charge if you plug the sync cable into the AC adapter? If so I would say it is your computer.
  3. ThrillHouseMD thread starter macrumors member

    Jul 11, 2008
    Yes, I exchanged the cable and still had the same results. It charges and syncs fine while the computer is on; I would just like to close the lid on my laptop and charge the phone as I sleep.

    Is there a minimum voltage required to charge the phone through USB? Is there some type of communication required between the USB/phone before the port will output power?
  4. fabian9 macrumors 65816


    Nov 28, 2007
    Bristol, UK
    I believe the voltage in USB ports is usually 5V?

    I think current is more of an issue here - the iPhone will not charge if the current it's provided with isn't high enough. I came across this problem when I bought a few car cigaret-lighter-to-usb connectors, some with higher, some with lower current output. Only the one with 1A current seems to charge the iPhone whereas lower currents wouldn't do the job.

    So I'm assuming something similar might be happening here. Whilst the USB port is powered, it may not be providing the same amount of current as when the computer is turned on.
  5. cobalt135 macrumors regular

    Dec 28, 2008
    Well, the USB spec. on voltage is 4.75v - 5.25v so if your computer does not output that in sleep then it is no go.

    My AC adapter outputs 5.12v and my MacBook Pro outputs 5.09v powered on or in sleep.
  6. cobalt135 macrumors regular

    Dec 28, 2008
    Max output current for USB is about 500mA. Now, the Apple supplied AC adapter can output 1A it does not mean that is what the device will use. The current used is really decided on by the device. Current is "drawn" by a device.
  7. ThrillHouseMD thread starter macrumors member

    Jul 11, 2008
    Hmmm... The Power Manager Help File might have shed some light on this:

    Enable Always On USB

    When this check box is selected, USB power is supplied even when your computer is in standby mode, in hibernation mode, or turned off. This function works only when the computer power is supplied through an AC adapter.

    Always On USB provides three modes: iPod® or iPhone™ digital devices, BlackBerry® smartphone, and Others. You can charge the USB devices listed below.

    Note: Not all iPod®, iPhone™, BlackBerry® smartphone, or other USB devices can be charged.

    An iPod or a BlackBerry can be charged only from the USB port marked with the following icon.

    Other devices can be charged from any USB port.

    iPod® or iPhone™ digital devices

    iPod nano MB261J/A
    iPod nano MA497J/A
    iPod classic 80G MB029J/A
    iPod Touch 8G MA623J/A
    iPod Shuffle 1G MB225J/A
    iPod nano 4G MA978J/A
    iPod mini 4G M9434J/A
    iPod nano 4G MA005J/A

    BlackBerry® smartphone
    BlackBerry 9920

    What an odd selection of supported devices... Does this confirm/debunk the voltage/current hypothesis?

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