I have a portable hard drive which I have tested with a USB amperage reader. At spin up it draws almost 700mA up for a few seconds and then around 300mA after. It works fine on the USB 3.0 ports on my desktop.

From what I know, USB 2.0 max amperage is 500mA and 3.0 is 900 mA.

However, on my laptop, if I plug it into one of my USB 3.0 port, it is either recognized quickly and dismounts or not at all. From my amperage meter it stays very high (almost 700mA) but jumps around, and stays high a lot for longer than if i plug it into my desktop 3.0 port. The drive doesn't work on any of the 3 USB 3.0 ports on my laptop and exhibits the same behaviour.

However, if (using an adapter) I plug it into my laptop's single USB-C port, it operates just as it does on my desktop.

Devices that draw under 500mA work fine on these ports, and with thumbdrives and video capture devices that I have used, they do indeed operate at USB 3.0 speeds. I've had a similar issue with a phone in the past, that had a USB C to A adapter (I ended up using a USB C to C adapter and it works fine.

Is it normal for USB 3.0 ports on a laptop to put out lower amperage than the 3.0 spec? Is there a setting for this? I have a MSI laptop. Thanks!

  • 1
    Perhaps it could be related to the cable making a bad connection, the USB 3 A->Micro B ones are notoriously unreliable. Try using a different cable if you have one
    – James P
    Dec 4, 2019 at 16:39

1 Answer 1


problem with motherboard and usb ports not putting out enough amps.

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