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I want to run an external HDD on a Pi (currently a first-generation model, I might replace it with a Pi 3 in the future). The drive has no extra power supply apart from its USB port.

Just plugging the drive into the Pi will not work, as the Pi cannot supply enough power. It does work, however, if I insert a powered USB hub.

This led me to the question: can I get rid of the Pi’s power supply, and just plug the power port of the Pi into another downlink port of the hub, having the hub power both the Pi and the drive? That way, I would need just one power supply for everything.

I have tried plugging the Pi into the hub (i.e. hub downlink to Pi power), without the drive connected, and the Pi boots up and works. To complete the setup, I would then connect the hub’s uplink port into one of the Pi’s USB ports, and plug the drive into the hub. Will this work, or should I anticipate problems (other than the hub supplying insufficient power to the Pi)?

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    @user68186 I am aware that the MicroUSB port is power only, and would use it only to draw power from the hub. For data, I would hook up the uplink port of the hub to one of the Pi’s USB peripheral ports.
    – user149408
    Mar 4 at 23:22

1 Answer 1

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Short answer: It works in principle, but the hub may not be able to supply enough power for the entire setup. Not recommended for production use.

I have taken the risk and in the meantime set up two Pis as described above:

+------------------------------+
|            USB hub           |
+--(uplink)---(port)---(port)--+
     |          |         |
     |          |         |
     |          |         |
+--(USB)----(power)--+   +----+
|         Pi         |   | HD |
+--------------------+   +----+
  • Pi 1: first generation, with a USB hub purchased recently (2022).
  • Pi 2: 3rd generation, with a USB hub purchased prior to 2011.

Both hubs are USB 2.0, with a power supply rated for 2.5A, which looks sufficient to me (the original Pi adapter is rated at 5.1V, 2.5A).

Initially everything worked, nothing got fried. Both Pis booted up and could access the hard disk. So the Pi does not seem to have any issues with a double connection to the hub per se.

After running this setup for a few months, however, power seems to be an issue. On both Pis I keep seeing the thunderbolt on the local screen, and get frequent under-voltage warnings. Every once in a while, the Pi stops responding, or loses its hard disk. Sometimes the disk does not spin up when I power on the system. All of this indicates power issues.

I tried replacing the USB cables involved (from the hub to the Pi and to the disk) with Y cables, which have a second USB A plug for extra power – to no avail, as the Pi still reports power issues. That indicates I have hit the limit of the hub as a whole, not of a single port. (These tests were only carried out on the Pi 3 so far.) If I power the Pi via the official power supply (which I have tested only briefly), power seems to be OK.

After a recent outage ended up corrupting the data on my disk, requiring a lengthy recovery operation, I started looking into alternatives.

Alternatives (if the hub setup is not stable enough)

Of course, you can power the Pi with its original power supply (or one specifically manufactured for the Pi).

Apart from that, Geekworm makes an enclosure, extension board and power supply tailored to the NAS setup I have in mind. I would get a (hopefully) stable power supply along with an enclosure that looks more professional than a Pi, disk and hub taped together. This allows me to keep the Pi 3 with its system setup, though I will need to buy the whole kit (about € 100) along with a new hard disk.

*If I am lucky, the external HD is a SATA disk with an external USB adapter, all mounted into an enclosure, so I can just rip out the disk and mount it into a SATA enclosure. However, many of these disks have a “native” USB interface and thus cannot be used as SATA disks.

You would need:

  • The X735 power & fan board, ca. € 30
  • The X820 SATA extension board, ca. € 40
  • The X820 Metal Case, ca. € 30
  • A 2.5" SATA disk of the desired size
  • A power supply (with the X735 V3.0, anything in the 6–30V range is OK)
  • A Raspberry Pi 3 (Pi 2 might also work; the Pi 1 or 4 are mechanically incompatible with the enclosure) and SD card

There is also the X835 board, designed for the Pi 4 and 3.5" SATA disks, and the matching enclosure. The X735 is compatible with both.

I haven’t had a chance to test these yet, but if I do, I will report back here.

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