Can't a USB hub power keyboard and mouse at same time?

08
2014-07
  • Haresh K Miriyala

    I'm trying to use a Dell mouse and keyboard via a single USB port using the USB splitter hub, but the devices seem to misbehave. Just one of the devices work when I connect both. I figured out it's a power issue. But, generally, the output of a USB port must be maximum 500mA and my mouse only needs 100mA, and the keyboard, 50mA at most. So, I assumed that both should work.

    I checked the voltages using the multimeter and the result was this: voltage of other 3 ports in my 4 port hub drops to 0.81 volts as soon as I plug in any device. The current output was maximum 0.18~ 0.2 Amperes. Is there a problem with my USB port (it's a USB 3.0 port)?

    • Answers
  • cde

    USB standard expects 5V ±5%. That's 4.75V to 5.25V to be valid. Between the Hub IC, the Keyboard and Mouse, something is bringing the voltage down enough for it not to work. Measure the current and voltage from the Upstream port, and see what it is.

    That said, I've had more (flash drive, wireless mouse, keyboard) on a cheap 1 dollar usb hub and it worked. Have you tried a different hub?


    • Related Question

    mac - MacBook USB-Hub
  • schneck

    I bought an active 7-port-USB-Hub to avoid all the cable mess on my desk. The following devices are plugged in:

    • Scanner (which is not being used, actually)
    • Keyboard
    • Mouse
    • Android-Phone

    When I now plug in a hard disk (passive, 2.5') as Time Machine device, it is not recognized. I wonder why this is the case, because it's an active hub. Do I really need to buy a hard disk with its own power supply?

    Another strange thing is, that when I plug the hard disk directly into the MacBook (beside the hub), it does not work either.


    • Related Answers
  • Arjan

    I believe the key here, is that he stated it's a passive 2.5" hard drive enclosure. That means that it may require two powered ports to have full power. The hard drive just may not be getting enough power.

    1. Is the hub plugged into a power outlet
    2. Does the usb cable have two ports? And are both being plugged into the usb hub?
    3. Does system Profiler see the drive?
    4. Does Disk Utility see the drive?
    5. What's the make & model of the USB Hub?
  • mouviciel

    Looks like the problem is not the hub but the disk.

    If it is visible from Disk Utility, try to format it with an HFS+ filesystem and a GUID partition table.

  • Arjan

    This does not explain why it won't work with the hub, but on the MacBook itself, all USB ports aren't created equal.