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I have two disks that I'd like to use inside a cheap USB 2.0 case. I can use the first one just fine, when I plug it the hard start spinning nicely and the disk eventually shows up on my computer. When I try to the other one in the external USB case, the hard drive starts a strange noise, as if the spinning could not start. The strange thing is that I can use both disks just fine when mounted directly on the mother board.

I would assume that a 12V/2A power would be plenty for the 2000G disk since marked with 0.75A. What am I missing in my setup ?

Working disk Not working disk
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Here is a picture of the power adapter:

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I am using a DELL Inspiron 3847, which per documentation should provide two USB 3. In which case the output power of those should be around 900mA which AFAIK should be plenty:

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For reference:

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    While spinning up, drives need a lot more power than specified. // Also note how the 12V PSU not only powers the drive but also the 5V converter and (parts of) the USB-SATA bridge board.
    – Daniel B
    Commented Nov 13, 2022 at 10:14
  • If you don't want to try a new PS, put a large electrolytic cap (perhaps 5,000 µF or more at 15 VDC rating or higher) across the PS leads inside the case. Observe polarity: plus-to-plus.
    – DrMoishe Pippik
    Commented Nov 13, 2022 at 19:53

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If the drive case is USB 2.0 then any USB 3.0 port it is plugged into will revert to USB 2.0. The USB 3.0 protocol may support 900 mA but USB 2.0 does not, so if the drive adapter lacks support for more power then the computer will tell the drive that it should not draw more power.

There's extensions to USB 2.0 and USB 3.0 to allow for more power than either protocol supports on its own. One is USB-BC and the other is USB-PD, and if the host supports one or both then it is possible to get 1.5 amps from the USB port. Also, not all USB ports will support the maximum power allowed by USB 2.0 or USB 3.0. It is unlikely but still possible that the USB port supports only 750 mA, or whatever, and this is insufficient for the larger drive and the conversion electronics. Given that the drive case uses a separate power supply the power supplied from the USB port is likely moot, the drive case should be getting all power from the power brick. If for some reason the drive case is taking 5 volts from USB and 12 volts from the power brick then it is still possible that you are seeing a lack of sufficient power because the adapter electronics is taking power in addition to the power the drive requires.

If we assume the drive case is taking all power from the power brick then you can still see a shortage of power because the adapter electronics takes power, and there will be conversion losses in stepping down the 12 volts to 5 volts. Given that the lower power drive works and the higher power drive does not then it appears it is simply a matter of the one drive requiring more power than the drive case can supply.

In short the part you are missing is how much power the conversion electronics consume. The power brick may be large enough to supply twice what the larger drive consumes but if the conversion electronics in the drive case takes the majority of the power supplied then there is simply not enough left for the drive to spin up.

Check the specifications on the drive case on how much power it can supply to the +5V and +12V pins for the drive, chances are that your drive is more than it can handle. If the drive case specifications don't tell you how much current it can supply to the drive then just your experimentation should indicate that the drive case isn't built to handle the drive.

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