Power source for HDs?


#1

Thinking of purchaseing your Plugable USB 2.0 10 Port Hub (with Power Adapter). Question: If i have 3 hard drive’s plugged in to the hub do I still need 3 AC outlets to power the hard drives, or does the hub have it’s own AC power source FOR the hard drives?


#2

Hi John,

Thanks for asking! The short answer is, if the drives have their own power supply, we’d always recommend using them rather than relying on USB bus power. The extra tangle of cables it worth it, to avoid power problems.

But the long answer is a little more subtle:

Any standard powered USB 2.0 hub provides .5A per port. On ours, up to a total of 2.5A for all devices (the capacity of the power adapter that comes with the hub). So 3 bus-powered USB hard drives are no problem – they’ll consume at most only 1.5A of the 2.5A available.

However, it’s common for USB hard disks, especially ones that have their own power adapter, to draw more than the USB 2.0 standard .5A (500mA) when relying on USB alone. That often works for one or two drives attached directly to a PC’s USB ports (root ports have more flexibility in allowing devices to draw more than 500mA). But this won’t work for drives attached through a USB 2.0 standard hub. [note: in the future things may improve with USB 3.0 supporting 900mA and USB 2.0’s BC 1.1 class allowing BC 1.1-aware devices to negotiate for 1500mA]

With only 500mA, you may see hard-to-diagnose problems like the drives starting then dropping off once they start drawing full power.

The problems can all be avoided by using the included power adapter, when drives have them (and thus may need them). Thus our recommendation to use them when possible.

Hope all that background helps. Just let us know if you have any other questions. Thanks again!
Bernie


#3