External SATA drive does not work without the optional USB cable *also* connected

I have Vantec NST-260SU external eSATA/USB drive enclosure (which came with an optional separate power supply - 5v/2A, while the drive needs a max of 1A) connected to a relatively new Windows 7 computer. The drive should work as a SATA drive with either the separate power supply or using a USB cable solely for power. I would prefer to use the external power supply because I have used all my rear USB ports.

Now, if I connect both the eSATA and USB cable, then:

1. The drive shows in the BIOS list of AHCI drives (and not in the list of attached USB devices).
2. Everything I can see about it in Computer Management seems to show it as a SATA driver (for example, it shows as "Location 0 (Channel 5, Target 0, Lun 0)" like my other SATA drives (and not "on USB Mass Storage Device" like my USB flash-drives).
3. It seems very fast, very much faster than my USB flash drives.

However, if I disconnect the USB cable and attach the power adapter instead, the drive does not show in the BIOS list and cannot be seen by Windows. The power LED on the enclosure is lit, and the drive enclosure becomes warm after running for a bit, so I am sure it is receiving power.

Does anyone know if this device requires both the USB and eSATA cable, and if so, why?

Or is there possibly something I need to do to reset the enclosure to not need the USB - the install instructions are pretty clear that you must connect the SATA cable before connecting the USB cable in order for the drive to function as SATA, which I am sure I did.

PS: I have reviewed the small manual which came with it, which has not been of help.

Solution 1:

The 5v power brick needs to be at least 1 amp of output, otherwise it will require USB power also.

See this document, near the bottom in the troubleshooting section.

http://www.vantecusa.com/system/application/media/data_file/nst-260_user_manual4.pdf

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