Thomas Vecchione wrote:
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.
My experience with notebook hard drives in external cases is they almost all work without either an external power supply or using 2 USB connections (2nd for additional power). I have 2 notebook hard drives here in external USB cases, and they both have worked fine on three Toshiba notebooks here (all low-end Toshibas), modern and very old Dell business laptops, Asus netbooks, a very old IBM Thinkpad, and HP/Compaq notebooks.
The older of the 2 external cases didn't cooperate with a decidedly-high-end Sony Vaio notebook; that required using the 2nd USB connection for extra power.
Since I was having trouble with the older external case mentioned above, I contacted the vendor. They pointed out that the drive controller circuitry draws power, in addition to whatever power the drive inside pulls. Apparently the circuitry in that older case was drawing just enough more to take power consumption over the limit and the notebook's USB power protection would shut off power to the device trying to draw too much power.
I can recommend Nextech's NX2 external USB drive housing, works beautifully and currently holds a Toshiba 60GB 7200RPM notebook hard drive. While it includes a 2-connector USB cable (2nd one just brings in USB power connection), I've never needed to use it.
I don't know what the impact of laptop power management might have on supplying current to USB ports when running on battery.
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