How many USB portable hard drives per hub?

[winkosmosis]

With USB 2.0 the max amperage was 0.5amp and generally you could run a single 2.5" hard drive per port. To use multiple per hub you needed an AC adapter.

But USB 3.0 max amperage is 2amp. Does that mean you can plug 3-4 hard drives into an unpowered hub?

 

[matreya]

With USB 2.0 the max amperage was 0.5amp and generally you could run a single 2.5" hard drive per port. To use multiple per hub you needed an AC adapter.

But USB 3.0 max amperage is 2amp. Does that mean you can plug 3-4 hard drives into an unpowered hub?

No, because the amperage on Mac USB3 ports is 0.95A.

 

[winkosmosis]

No, because the amperage on Mac USB3 ports is 0.95A.

Thanks, I didn't know the max was so low, I figured the spec required 2A

 

[marzer]

Thanks, I didn't know the max was so low, I figured the spec required 2A

I haven't confirmed it through another source, but this is from the USB Wikipedia page:

"As with previous USB versions, USB 3.0 ports come in low-power and high-power variants, providing 150 mA and 900 mA respectively, while simultaneously transmitting data at SuperSpeed rates.[25] Additionally, there is a Battery Charging Specification (Version 1.2 – December 2010), which increases the power handling capability to 1.5 A but does not allow concurrent data transmission.[22] The Battery Charging Specification requires that the physical ports themselves be capable of handling 5 A of current[citation needed] but limits the maximum current drawn to 1.5 A."

 

[ColdCase]

Regardless of power, hanging more that two USB3 drives off a USB3 hub is not reliable with many hubs. It is a USB3 thing, the simpler USB2 drives did not have as many issues. But multiple drives on a USB hub connected to a Mac has always been problematic.

 

[Mr. Retrofire]

But multiple drives on a USB hub connected to a Mac has always been problematic.

Especially if you use USB 3.0 hubs with more than one USB 3.0 hub controller chip (all USB 3.0 hubs with more than 4 ports).

 

[William Auld]

With USB 2.0 the max amperage was 0.5amp and generally you could run a single 2.5" hard drive per port. To use multiple per hub you needed an AC adapter.

But USB 3.0 max amperage is 2amp. Does that mean you can plug 3-4 hard drives into an unpowered hub?

My USB 3.0 hub supports only two drives, the third one i have to plug to my mac.