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External drive without power supply

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March 7, 2011 2:22:26 PM

Hello,
Why do some external HDs use power cords and some do not? Does one work better than the other? I can't decide which to buy.

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a b ) Power supply
a c 415 G Storage
March 7, 2011 3:13:02 PM

2.5" laptop drives are designed to run with a lot less power than 3.5" desktop drives because they're usually used on battery power. They're slower, but a lot less power-hungry. If the external enclosure you're buying contains a 2.5" drive then the amount of power that can be delivered over a USB connection is sufficient to run the drive. But if the external enclosure has a 3.5" drive inside it then USB can't provide enough power to run it and you need to plug it in to a power outlet using one of those "power bricks".
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a b ) Power supply
a c 289 G Storage
March 7, 2011 4:10:10 PM

It's a little worse than sminlal wrote. I have two external 2.5" drives from (I forgot the brand! They're at home. Good brand). One works nicely on USB power. The other will not run on the power from most USB ports and came with a Y cable that attaches to two USB ports, drawing only power from one.

Better depends on the use: for travel, I would be careful to choose one that can thrive on the power of one USB 2.0 port (or 3.0, if that's what you have). For home, I settle for the ensured operation of external power.
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a b ) Power supply
a c 415 G Storage
March 7, 2011 5:42:32 PM

WyomingKnott said:
The other will not run on the power from most USB ports and came with a Y cable that attaches to two USB ports, drawing only power from one.
Sounds like it could be one of the new 750GB or 1TB 2.5" drives that have more platter than the usual laptop. As well as taking more power, those drives are taller than a standard laptop drive and actually won't fit into most laptops with standard drive bays.
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a b ) Power supply
a c 353 G Storage
March 7, 2011 6:04:05 PM

Siminlal, what WyomiingKnott indicated is true for some of the older drives (=< 500 gigs). One reason may be the diff between 5400 and the 7200 RPM; But also, there are some of the 2 1/2 in drives that draw sligthly more than the max 5 Watts. I also had that problem with the "older" low capacity drives. Additional reason my be the differece between drives on there INRUSH currents which shuts down the usb power (senses OC) even if the normal current is under 5 W. Reason for this is that most of the drives have a lower idle/read power than when they write.

My recommendation: I always use a powered hub to attach HDDs to my laptops.
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March 8, 2011 9:47:57 AM

Thanks to all for your replies.
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a c 78 ) Power supply
a c 152 G Storage
March 8, 2011 2:27:37 PM

It depends allot on the motherboard you have as well. For instance, My P35 DS3R will NOT run external 2.5 inch drives on its front ports(the back ones are fine, guess they want to play it safe, they have full control over the traces on the board that lead to the rear ports, but not the wires in your case). The current limiter kicks in @ 2.5 watts, yes its only 2.5 watts not 5watts. 0.5A X 5V = 2.5watts

That said my old compaq R3000, H55n-USB3 and every Asus board i ever owned power just about anything off its usb ports. Even ran a satellite radio unit rated @ 2 amps on it :) 

Either way, with those Y cables you should have no issues with any 2.5 inch drives.

Every 2.5 inch drive i had only needs this power to get spinning, after that, one usb port was able to keep them running along.

For my money, I would go with ESATA/External power(3.5) for speed every time(desktops). For a laptop, USB/Power-ESATA(this is a usb/esata port combo) or USB3(it has more power and speed, no faster then esata with current drives, but may become standard soon)
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March 14, 2011 12:26:48 PM

I bought a Seagate 250 GB with a 2.5" drive and USB cable for under $40 from NewEgg. I needed something mainly to back up my digital photos. I also backed up my MSOffice Suite. So far, it is meeting my needs and is so easy to use. I do have an ASUS motherboard and I am plugging it into one of the front ports of my desktop. It isn't lightning fast - but it is fast enough, especially for the price!
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March 14, 2011 12:27:53 PM

Best answer selected by cwilli.
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August 6, 2011 2:27:41 AM

May I ask , let's say an External HD can already run on power from 1 USB port. But if you mistakenly plug in the 2nd cable from a Y cable to a second USB port.

Will there be any danger of damaging the Hard Drive?
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