As was already mentioned before, USB spec is far less than the power
needed to power a laptop hard drive. Many USB implementation break
this spec and provide more power, but just because a hard drive
doesn't work, doesn't mean a USB port doesn't provide power. The only
type of HD that MIGHT be able to work under USB spec, and I would want
to check this, is a SSD.
Also as was mentioned, all USB ports provide some power, and so long
as the device is within spec, they will get the power needed. It
takes much more power to spin a motor in an external drive than it
does to power a non-moving device. For the record, the power draw for
that UA25 is 480mA as listed on the site, so it appears to be within
spec(Albiet on the very high end of it:)
Seablade
PS By the way, you can conceivably damage a proper in spec USB ports
with those 'bus powered' hard drives IIRC. I wouldn't ever trust them
myself.
On Mon, May 2, 2011 at 6:10 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote:
> On Mon, May 2, 2011 at 2:36 PM, Arnold Krille <arnold@xxxxxxxxxxxxx> wrote:
>> On Monday 02 May 2011 23:17:05 Mark Knecht wrote:
>>> OK, so I guess obviously the USB port must supply some amount power or
>>> even a simple flash drive wouldn't work as the memory in it has to
>>> require some sort of +/- supplies to function at all.
>>> In terms of my external USB hard drive, I have 3 like the following
>>> link except mine are 500GB.
>>> http://www.amazon.com/Buffalo-Technology-DriveStation-External-HD-CX500U2/d
>>> p/B002IYDEMW
>>> This drive ships with an external wall wart power supply and doesn't
>>> function without it on any machine I've plugged it into.
>>
>> Yep, that device will not work when used only on usb-power. The 3.5" disks
>> need 12V, which the usb doesn't provide.
>>
>> What I have here and what works with one connector on my laptops and needs two
>> on my desktops is a case for a 2.5" disk. (The disk I got from my brothers old
>> laptop.)
>>
>> Have fun,
>>
>> Arnold
>
> OK - I have an old laptop SATA drive around here. Maybe I can pick up
> a small case at Frys and then use it to test.
>
> Thanks for the idea.
>
> Cheers,
> Mark
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