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I bought an external powered usb hub thinking that it may be useful as I could not connect 2 external usb hard drives on my computer at the same time?

But now when I plug it in I still see the same issue. What is the problem.

What are external powered Usb hubs used for then?

Devices:

My host machine is Windows 7, running Intel i7 processor.

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They are used for providing power to many usb ports. Much more power than your PC could supply alone. If you need an answer to your problem, I got none. –  wolfo9999 Aug 12 '12 at 5:24
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what devices are you connecting? a powered hub simply allows the devices to pull a little more power, but there is still a maximum: see my answer here: superuser.com/questions/330556/… –  MaQleod Aug 12 '12 at 5:24
    
may i knew your hardware configuration?i.e motherboard and bios capablities –  BlueBerry - vignesh4303 Aug 12 '12 at 5:26
    
what's the exact problem you're facing? –  Sathya Aug 12 '12 at 5:30
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In case a port needs more than 100mA. Say a non-powered hub is supplying power to a keyboard, a mouse and a wireless adapter. You then want to plug in a hard drive that pulls 500mA. Once you do that, the hard drive doesn't work as the hub cannot supply it the power it needs. If you replace it with a powered hub, all the devices still get their 100mA minimum, but the hard drive can request 500mA to that port. That 500mA maximum must be shared with the other ports, but they'll always draw that initial 100mA regardless. –  MaQleod Aug 13 '12 at 15:24

2 Answers 2

If one of the drives isn't appearing on your computer when plugged in directly, it's possible that the drive itself has died. In that case, plugging it in through a hub will have no additional effect.

If the hard drives are of the smaller 2.5" variety and are powered via USB (with no power adapter), it's also possible that there's only enough power for one drive. Do both drives work when plugged in one at a time?

If you did have multiple working drives, but not enough USB ports to attach them all, you could use a USB hub. However, that assumes that you have enough power in the first place to run the drives.

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They are especially useful on laptops, as laptops have a limited amount of power they can output USB ports. If you try to connect a lot of devices which are 'power-hungry', like external hard drives, external monitors, DJ controllers, etc. they might not work.

For example, my laptop has 3 inbuilt USB ports. If I connect a USB hub to one of them, and then connect say 4 external hard disks in all, 1 or 2 of them do not work. If I connect an external powered hub, they work because the hub provides the power from the wall outlet, not from the laptop.

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