Powered USB HDD - vs Self powered USB -- load on computer ?

  1. Posts : 11,246
    Windows / Linux : Arch Linux

    Powered USB HDD - vs Self powered USB -- load on computer ?

    Hi there

    Intuitively one might think using Powered (from the mains) external USB HDD's would require more power from the computer as well compared with those small self powered units.

    I've no way to measure this but I'm sure the small units might consume MORE power as the computer has to supply all the power for Disk rotation and the USB I/O controller.

    I only ask this because I need to put two large powered USB units (both with 2 X 3 TB Raid 0 HDD's in each unit) on to a USB 3 Hub.
    The two HDD units seem to perform perfectly well whether connected to the chargeable port on an HP laptop or the "non chargeable" ones.

    The RAID 0 is powered by the HDD itself (internal Hardware RAID) --used RAID 0 for speed -- don't need to mirror etc - I've enough backup if the whole thing goes bonkers. !!

    The files on these HDD's are serving music and video so not intensive used -- don't seem to have any problem streaming media from the laptop.

    Any engineers out there - curious over what is the actual load (power wise) on the computer if a POWERED USB HDD is used compared to a Self powered one. Note the Hub I'm using is not also powered.

      My Computer

  2. Posts : 4
    Windows 10 Pro

    We can suppose that a portable HD enclosure that has it's own power supply doesn't draw as much current from the 5 volt supply provided by the USB bus.

    On a purely practical basis it simply doesn't matter. There are hard limits to how much current a USB port will deliver. USB 2 ports are limited to 500 mA, which is why they can be so bad for charging smart phones & tablets. A USB 3 port supports up to 900 mA.

    The load presented to the host is not relevant. The external device either works or doesn't.
      My Computer

  3. Posts : 15,118
    Windows 10 IoT

    How much power they need depends on the drive(s) in the enclosure. A full size spinner will need a lot more juice than a say a smaller laptop drive. An SSD will need even less power. A 10,000 RPM drive will draw more current than 7200 RPM drive, and 7200 RPM drive more than 5400 RPM drive. In most cases. More platters means bigger motor etc. Lots a variables. As mentioned above USB ports are current limited and will just shut down when overloaded. A self powered enclosure likely draws no power from the PC, Data only.

    I made my own custom USB cables for my Raspberry PI SBC. It is limited in how much current it can supply via the USB ports. It can't do the 500ma per port. I connect Data only from The Pi's USB port to the USB device. Power to the device comes directly from a 10 A 5V power pack, that also powers the Pi. No power drops or overloading the PI's USB ports. It basically does what those externally powered enclosures do. No load on the USB port.
      My Computer


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