Hi,

I have a Mac Mini and a whole bunch of portable USB hard drives that I use for storage and backup with the Mini working as a network server running Lion Server. Anyway, this setup works quite well except for the issue of how to connect the drives to the machine. With one drive, it can plug in quite nicely. With two, there begin to be power issues. Any more than two and it is drawing too much power through the USB ports.

So I thought to myself, that's easy enough to fix; I'll just get one of those powered USB hubs that claims to be able to power high-draw USB devices. And I did. And it can only power two drives instead of one in each of its ten ports.

Any suggestions? I don't want to have to have one USB hub for every couple of drives. That would just make the whole setup completely useless, as I switched from large externals requiring external power supplies of their own specifically for the purpose of only having to have one power supply for many drives. I'd be perfectly OK with purchasing a new hub or other device like that to be able to power the drives if someone has one in mind that can actually pump out enough juice to do many at a time without a problem. The drives are 1.5TB Seagate Expansion drives (USB3) and are all less than 2 months old.

Thanks,

JC

Check and see how much each device draws one by one. You can do this through the System Profiler; then goto the USB header on the left and find your devices. Everything draws power so just see if there are any other things taking up power. It will tell you available power and what is currently being used.

Also you might want to look into getting power adapters for the drives

USB 3.0 specifications are 5V, 5Amps but some devices draw more current than that. My guess is that your USB hub only offers 1Amp. (The value will be written on the power adapter.)

Consider buying a more powerful wall adapter for your current USB hub. It should overcome the problem. Digikey has a lot in stock. (I have no affiliation with Digikey except as a satisfied customer)
Power Supplies - External/Internal (Off-Board) | AC DC Desktop, Wall Transformers | DigiKey (http://www.digikey.ca/product-search/en/power-supplies-external-internal-off-board/ac-dc-desktop-wall-transformers/589898?k=5v%20power%20adapter)

If I plug in a more powerful adapter for the hub, will it just power the drives or could I damage the drives and/or the hub?

This is what I see in the information. It appears that it's only using less than 100mA so there should be plenty for quite a few drives.

No, you shouldn't have any problems adding a power adapter with more current, so long as it's 5V.

I'm not sure what to tell you about the hub and the 100 mA issue.

Edit: This article (http://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to-avoid-blowing-up-your-smartphone) explains a bit about USB and how it works with devices drawing different current.

This is what I see in the information. It appears that it's only using less than 100mA so there should be plenty for quite a few drives.

JC -
As you suspected in your initial post, the drives you have just draw too much power.

That reading of less than 100ma that the Mac gives you is totally useless.
The Mac doesn't actually measure the current, it just reports a value.

I have come across that a hundred times before, right now I have a 120 GB USB 2.0 drive plugged into a Mini, it shows as drawing 2 ma from the Mini - there is no way one can get a hard drive of any size to spin with 2ma at 5 volts - and spin it does, also shows up on the desk top.
I don't have my USB current meter here but the current draw of my drive is more than 100ma. If I plug it into a non-powered USB 2.0 port which delivers 100 ma (rather than the 500 ma of a powered 2.0 USB port). my drive won't spin up.

With USB 3.0 drives the situation is worse, the USB 3.0 spec requires the USB 3.0 port to deliver at least 900 ma vs 0nly 500 ma for a USB 2.0 port, so a USB 3.0 drive that draws say 700 ma (just to make up a number) will work fine on a USB 3.0 port but not necessarily on a USB 2.0 port even if you have the adapter cable.

I looked high and low for a technical test review of the 1.5 TB drive you have, couldn't find anything that measures how much current the drive actually requires, but I can guarantee you, it takes more than 100 ma to spin up a 1.5 TB drive.

How many of those USB drives do you have that you want to power at the same time?

The real solution is to buy some AC adapters for the external drives and not rely on USB power. Is the convenience really worth the very real possibility of data corruption when drives start dropping off the Desktop at random because the USB power is unstable for a herd of drives?

That's exactly the details that I needed. I am now running ten drives with a 5V 10A adapter and they are working perfectly, all USB 3.0 drives. This saves me so much bother with cables, which was most of the point. Now the solution is expansible to multiple hubs and fairly inexpensive with only one adapter per ten drives. From using an inline meter, it appears that they are drawing about an amp each at peak use so 10A per 10 drives is definitely sufficient.

Thanks for your help!

J

JC -
As you suspected in your initial post, the drives you have just draw too much power.

That reading of less than 100ma that the Mac gives you is totally useless.
The Mac doesn't actually measure the current, it just reports a value.

I have come across that a hundred times before, right now I have a 120 GB USB 2.0 drive plugged into a Mini, it shows as drawing 2 ma from the Mini - there is no way one can get a hard drive of any size to spin with 2ma at 5 volts - and spin it does, also shows up on the desk top.
I don't have my USB current meter here but the current draw of my drive is more than 100ma. If I plug it into a non-powered USB 2.0 port which delivers 100 ma (rather than the 500 ma of a powered 2.0 USB port). my drive won't spin up.

With USB 3.0 drives the situation is worse, the USB 3.0 spec requires the USB 3.0 port to deliver at least 900 ma vs 0nly 500 ma for a USB 2.0 port, so a USB 3.0 drive that draws say 700 ma (just to make up a number) will work fine on a USB 3.0 port but not necessarily on a USB 2.0 port even if you have the adapter cable.

I looked high and low for a technical test review of the 1.5 TB drive you have, couldn't find anything that measures how much current the drive actually requires, but I can guarantee you, it takes more than 100 ma to spin up a 1.5 TB drive.

How many of those USB drives do you have that you want to power at the same time?

Wow! Ten drives? That's a lot. And all for backups. Hmm sounds like quite the setup!

The real solution is to buy some AC adapters for the external drives and not rely on USB power.

This is not as easy as it sounds with laptop external drives.

Only about half of mine have provisions to supply external power, ie a 5 volt jack.
The rest have a single USB connector and an LED - that's it.
To feed external power into those one needs a special USB cable.

Ten drives for storage, ten exact duplicates for backup. Ten on one hub, ten on another. Nightly backups. It works quite well. Works out to be just over 12TB of data at the moment, duplicated exactly for full redundancy.

J


Wow! Ten drives? That's a lot. And all for backups. Hmm sounds like quite the setup!