USB-C Power Hub: Working Out the Current Budget
The difference between a hub that works with drives and one that does not is usually a small DC socket and a few dollars. Buying without checking is the usual reason for drives that disconnect.
Quick Answer
A bus powered hub takes all its current from the host port, typically 900 mA at 5 V on USB 3.x, divided between every port. A self powered hub has its own supply and can give each port the full 900 mA or more, which is what external drives need. If the hub will run any mechanical drive, or several devices at once, choose self powered.
Current Budget Comparison
| Hub type | Total available | Per port | External drive |
|---|---|---|---|
| Bus powered, USB 2.0 host | 500 mA | Shared | Fails |
| Bus powered, USB 3.x host | 900 mA | Shared | Marginal for one SSD |
| Self powered, 5 V 2 A supply | 2 A or more | Up to 900 mA each | Works reliably |
| Self powered with charging ports | Higher total | Port specific | Works, and phones charge faster |
| Hub with PD passthrough only | Charger dependent | Power to the laptop, not the ports | Ports still share bus power |
Symptoms of Insufficient Power
Drives disconnect under load
The drive spins up, then disappears during a large transfer. This is the classic symptom.
Clicking or repeated spin up
Mechanical drives need a surge at start up that a bus powered hub cannot provide.
Devices present at boot then missing
All ports starting at once exceeds the budget.
Slow charging
Phones and tablets take hours because the shared current is small.
Choosing a Self Powered Hub
- Check the supply rating, not just that one is included.
- Confirm the per port maximum current.
- Count the drives you intend to run simultaneously.
- Check whether PD passthrough is separate from port power.
- Prefer a locking or screw fitting DC input for fixed installations.
Real-World Applications
- Running two external SSDs from a thin laptop.
- A desktop bench with several test devices.
- A photo or video workflow with card readers and drives.
- Powering peripherals where the host port is limited.
Related Guides
For charger sizing, read USB-C hub with power delivery. For charging only units, see USB charging hub. For port counts, start with USB-C hub with multiple ports.
FAQ
Can a bus powered hub run an external drive?
One SSD sometimes, unreliably. Mechanical drives need a self powered hub or a powered enclosure.
Does PD passthrough power the hub ports?
Not usually. Passthrough charges the laptop, while the ports still share the host current.
How much current does a 2.5 inch SSD need?
Up to about 1 A at 5 V briefly, though average draw is far lower.
Is a bigger supply better?
Up to a point. A supply that exceeds what the hub can distribute gives no extra benefit, but margin helps stability.