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I'm having issues connecting a 3.5 inch WD Caviar SE (WD3200AAJS) via a SATA to USB adapter. The drive is recognized, but it doesn't spin, so it just shows up with a capacity of 0 bytes.

Note that the adapter I'm using is originally for 2.5 inch drives. Connecting a Seagate Momentus (2.5") drive works just fine. I've read somewhere that it doesn't matter if the drive is 2.5 or 3.5 inches, so long as it's SATA. Also, when I connect the power cable from the desktop PC to the WD drive, it spins normally. That's just to confirm that the drive isn't generally broken.

Can anyone point me in the right direction? One theory I have is that the WD drive might need to have different jumper settings for this to work. Then again, my laptop already recognizes it, it just doesn't spin... So perhaps it's just not getting enough power through the USB cable?

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up vote 12 down vote accepted

It does matter what size the drive is. Large 3.5" hard drives require more power then what even two USB ports can provide. For reference, a single USB port can provide a maximum 500 mA of current. A Western Digital WD3200AAJS, on the other hand, requires 1444 mA at idle, and 1608 mA when reading/writing files to/from the drive.

It is part of the USB specification that if a device attempts to draw too much power, it is simply disconnected from the target system - this is why, while your adapter itself shows up, you can't access the drive. There is no jumper setting to change, SATA drives don't have any.

What you're trying to do is, quite bluntly, impossible. You'd need the power of almost four USB ports to get the HDD working, which is also why you never see full 3.5" drive enclosures without an external power supply.

Your only option is to power the drive from the computer, power it using an external power supply, or if you can find any (reliable) +5V and +12V DC source, you could hack together your own. Or you could just buy a USB HDD enclosure that has the power source.

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Ok, thanks. I'll get myself a USB HDD enclosure then, that'll cut the hassle down to a minimum. – Brokenstuff Aug 15 '11 at 17:05
Hello, can I just ask what about the possibilities of a) newer USB 3 superspeed power outpuit (900mA??) and b) using another computer's 12V power to power the drive (would the grounds need to be connected etc even if plugged into the same mains connection). – Wilf Apr 22 at 14:36
@Wilf technically, using a single device that draws power from more than one USB port (e.g. using a Y-connector) is non-compliant with the USB specification - from Use of a 'Y' cable (a cable with two A-plugs) is prohibited on any USB peripheral. If a USB peripheral requires more power than allowed by the USB specification to which it is designed, then it must be self-powered. – Breakthrough Apr 22 at 16:46
@Wilf In the case of using a secondary 12V source, yes you would need to connect the ground of the device's power supply to the ground of the computer (which you can do by simply connecting it to the ground/zero-volt wire of the USB cable itself, since it shares the same ground as the power supply of the computer). The mains AC supply ground is not the same as the ground rail provided by the DC supply, it just becomes the reference for what zero volts is, with respect to the voltage rails the power supply provides (which can be both positive and negative). – Breakthrough Apr 22 at 16:56
Thanks, I thought that idea would end up a bit more complicated :) – Wilf Apr 23 at 22:58

A single USB cable is not sufficient to power most 3.5" drives (which is why you might have seen some crazy USB Y-adapters on certain enclosures-- those are to draw power from two ports and power the drive without an external adapter), but it can power a 2.5" drive. You will need to get a proper external enclosure that can support the power requirements of a 3.5" drive.

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Well, I do have a Y-cable - seems that's not enough, though. – Brokenstuff Aug 15 '11 at 15:16
Then I would guess that you need an enclosure with an external power supply. Perhaps it's a particularly high-power device, or needs more than usual to spin up. In any case, I wouldn't expect a self-powered 2.5" adapter to provide sufficient juice for a 3.5" drive. – Darth Android Aug 15 '11 at 15:21

A 3.5" drive requires both 5v and 12v, wheras 2.5" drives only need 5v. USB only supplies 5v. USB adapters/enclosures for 3.5" drives have a separate 12v input in addition to the 5v, which can be supllied by the USB bus or by the power supply, in which case the PSU is supplying both voltages.

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