How many usb 3 devices can a single usb c port power through a hub?

More specifics would be needed. What computer, what hub, and what devices? If it's a USB 3 port it should theoretically be able to provide 900 mA to an unpowered USB 3 hub, and then the power distribution would be negotiated. If it's an unpowered USB 2.0 hub then it would be 500 mA. If unpowered, the hub itself needs to reserve some power for its own operation such as lights and communications.

Powering peripherals through USB - Apple Support

I don't have a USB 3 hub, but I do have an unpowered 4-port USB 2.0 hub. On my hub I currently I have a SanDisk Cruzer Micro that reports a current requirement of 200 mA, and a Logitech Nano receiver with a current requirement of 98 mA. The hub reports it needs 100 mA. So that's 200+98+100=398 mA. So the 500 mA that the port provides is enough. If it's not then there will be some sort of warning message. I just plugged an iPad mini into the hub and checked again. It's actually reporting the iPad mini needs 500 mA but nothing else has changed. It's not charging though. Obvious battery powered devices can back off of using current.

If you directly plug in an iPhone or iPad it can actually provide an above-spec 2100 mA.

Sorry - gave you an overly technical answer. Again - it really depends on what drives. Back in the day, a lot of external bus-powered drives came with cables with two USB-A plugs. They recommended using a second one simply to draw more power. I haven't seen one like that in years. Most modern drives require much less power.

Just as an example, I've got a Seagate Backup Slim external drive. When plugged directly into a USB 3 port, it's reporting 900 mA available current but 144 mA required. When I plug it into my unpowered USB 2.0 hub, it's reporting 100 mA available and 100 mA needed. I don't quite understand what's going on, but it's working. I think a second one might even work as long as there's enough available current for all the devices. I'm pretty sure they play certain tricks with the power supply, because bare drive specs say that they need more than 144 mA during startup and writing.

I also have another drive in a Patriot Gauntlet 2 enclosure. I can't get it to work on the hub at all. But if plugged directly into my USB 3 port it says that 900 mA are available and that it requires 898 mA.

cineclepix wrote:

Thanks for the info!

I work in video and I have a project coming up that's going to require dumping cards to recycle and keep shooting. Just bought a 13in MBP (only two ports) I was hoping to use them to power 2 Seagate 4TB Backup Plus externals and a RED mini mag station which (like the older drives that you mentioned) has the option to be powered from a second USB 3 connection. I'm just trying to cover all of bases for situations in which there is no AC option.

The double-plug setups were actually needed back in the USB 2.0 days when USB 2.0 ports were only rated as putting out 500 mA, and when hard drives tended to use more power than they do today. I'm not sure they really need two if plugged into a compliant USB 3.0 port. I've never had one fail to work with a single plug going directly to the computer's port.

You can find out what the current demand is using System Report. I'd recommend plugging them in (one at a time) without a hub to find their current requirement. Of course eject the disk when you move to the next one. Click on the little apple in the upper left corner and select "About this Mac". Then click on the button on the bottom that says "System Report". Click on Hardware>USB to get the USB Device Tree. You should see the drive under "USB 3.0 Bus". You'll see a whole lot of stuff, but this is what I see (minus the serial number which I've blanked out):

BUP Slim BK:

Product ID: 0xab24

Vendor ID: 0x0bc2 (Seagate LLC)

Version: 1.00

Serial Number: ********

Speed: Up to 5 Gb/sec

Manufacturer: Seagate

Location ID: 0x14300000 / 2

Current Available (mA): 900

Current Required (mA): 144

Extra Operating Current (mA): 0

BUP Slim BK:

I'm not sure about the 4 TB version, but you can see what it says. If you have a hub you can see what it requires. This is what mine says:

USB 2.0 Hub:

Product ID: 0x0101

Vendor ID: 0x1a40 (TERMINUS TECHNOLOGY INC.)

Version: 1.11

Speed: Up to 480 Mb/sec

Location ID: 0x1a120000 / 3

Current Available (mA): 500

Current Required (mA): 100

Extra Operating Current (mA): 0

I know we've been arguing back and forth on another topic about external drives and enclosures, but for your purpose that Seagate drive might be ideal. It probably requests less power than a separate enclosure/drive combination, which will typically reserve as much power as it can get just in case the drive needs it.

As an example, I believe that I would be able to operate three of my 1 TB Seagate BUP Slim drives with a proper USB 3.0 hub. Not sure about the other device. OK - found the specs:

http://docs.red.com.s3.amazonaws.com/955-0047/REV-AC/HTML/955-0047%20Rev-AC%20%2 0%20RED%20PS,%20DSMC%20Media%20Operation…

It says it needs 5 V, 2 A, which is well past the USB 3 specs for even two ports.

What MBP though? Is it one of the new ones with only USB-C ports? If you need a USB-C hub with USB-A ports, then I imagine it should be more than adequate since they typically draw a lot of current.

Since you are wanting to transfer videos/graphics/images, I would not consider using any peripheral that is not self powered (with an adapter) and/or, at the very least, use the computer plugged in to power. Those kinds of tasks are processor/RAM/power hungry. My solution would be more cards.

babowa wrote:

Since you are wanting to transfer videos/graphics/images, I would not consider using any peripheral that is not self powered (with an adapter) and/or, at the very least, use the computer plugged in to power. Those kinds of tasks are processor/RAM/power hungry. My solution would be more cards.

Those things are $850 each, so I get the incentive to dump the data and recycle the modules. If the MBP is just being used to move data from the modules to the hard drives, it's not necessarily going to tax the CPU like video editing would. Sounds like a live-shoot environment without access to power.

But if it's really needed, a car battery hooked up to an inverter might work for providing extra power. There are purpose-built supplies too, like this one:

http://www.jackery.com/power-bar.html

Amazon.com: AC Outlet Portable Charger, Jackery PowerBar / Explorer 20800mAh 85W (100W Max.) Travel Laptop Power Bank & …

This one should be able to double the time using the AC adapter. Not sure if it could power a USB-C MBP though.

babowa wrote:

A camera card for $850? Really?

$850 is just the 120 GB version. The 960 GB version is $2950. This is specialty equipment used for professional video/movie production. Of course the camera body/sensor costs upwards of $80,000. The reader is only $195.

http://www.red.com/store/media

I'd heard of this company before when I was looking for a job. Here's a review of the Red Weapon Dragon. The storage module is inserted at 4:11.

Dope Tech #1: Weapon! - YouTube

cineclepix wrote:

Just in case anyone else was curious, the answer is 1 Thunderbolt 3/USB C port will power 2 Seagate 4TB drives and a RED Mini Mag Station but all three devices crash if you try to copy to both Seagate drives from the RED Station simultaneously.

Unplugged 1 Seagate and no problems. Expecting a second Thunderbolt 3 to USB A cable tomorrow (for whatever reason B&H shipped my cables separately from the MBP) so I'm assuming that I'll have no problems running everything from two ports.

Thanks again for all of the info everyone.

Not surprised. That media reader has a huge current draw for a portable device, and the bigger drives probably need more current than mine. Did you check what the current requirements are in System Report for the devices and hub? Running the Red reader directly off the USB-C port is probably the best thing you can do since it's supposed to be able to provide up to 3000 mA if used directly without a hub. With the hub it might work in standby mode, then crash when it needs to perform transfers.

Another issue is that there can be problems if a device is incorrectly reporting its current requirements and there's a surge beyond what the source can provide. I've got a (USB 2.0) LaCie Little Disk, and it's reporting it needs 0 mA when using USB. It does work, but only if it's plugged in directly.

Are the drives fast enough to receive the data? There's a certain amount of overhead in USB, and using a hub complicates how the data is sent to multiple devices.

A camera card for $850? Really?

You appear to be in such capable hands, I will try to help elsewhere. Good luck!