w_tom said:
How much power does that drive consume from the USB port? How
much does the OS let a USB device consume? Less than 10 watts. That
is a maximum number - 10 watts. But only you can provide the number.
What is it?
. Missing are other numbers from your Windows XP hardware. For
example, how many amps can that power supply provide on each voltage?
How much of that is being consumed by other devices? Only you have
those numbers. How can a useful reply occur when important hardware
numbers were not provided?
You snipped the most important part of the post.
"I intend to connect the harddisk to a USB hub which has
a seperate power supply. Does that help?"
Yes, it does help.
And that means the question has nothing to do with the PC
and its power supply. There are two cases, the first with
an external 2.5" enclosure, and the second with an external
3.5" enclosure. (Those are the two sizes commonly available.)
bus
(1) PC --------- Hub ------------- 2.5" drive
| powered in enclosure
|
Adapter
|
A.C.
In this case, the 2.5" drive will draw somewhere
around 5V @ 500mA or about 2.5 watts. The adapter
on the hub provides the power.
If the 2.5" drive needs more than 2.5 watts, some
of them come with two USB connectors on the end of
the USB cable. That allows close to 5W to be drawn
from the two connectors total. While the "hydra" style USB
cable used to be popular, it is hard to find examples
now of this cable, to show people.
Example of a 2.5" external drive.
http://www.newegg.com/Product/ProductReview.aspx?Item=N82E16822136139
There are also, apparently, adapters for powering
the drive, if the drive is not working properly
with bus power.
This external enclosure for a 2.5" drive, includes
a power adapter. The 2.5" (laptop) hard drive is purchased
separately. This is an example of an enclosure "kit".
http://www.newegg.com/Product/Product.aspx?Item=N82E16817345004
This second method, was used for a few of the 2.5" external enclosures.
USB Y cable (for 5V at 2 x 500mA). One USB uses four wires,
the second one uses two wires (+5V and GND). The two wire USB
connector makes room for 500mA more current to flow. This kind of
adapter cable is used with some laptops, if the drive appears to be
struggling to get enough power. Some laptops police the power draw,
more closely than a desktop computer. This adapter can help. I
cannot find a picture right now, that pictures the connectors
clearly, so I'm going to have to draw a diagram.
http://c1.neweggimages.com/NeweggImage/productimage/17-387-021-04.jpg
USB#1 +5V --------------+
GND ----------+ |
| |
USB#2 +5V ----------|---+--------------- 2.5"
GND ----------+------------------- Hard
D+ ------------------------------ Drive
D- ------------------------------ Enclosure 5V @ 1A max
(2) PC --------- Hub ---------- 3.5" drive
| |
| |
Adapter Adapter (13W+)
| |
A.C. A.C.
A 3.5" drive uses both +5V (logic board) and +12V
(motor or perhaps actuator). Total power drawn at idle,
is around 13 watts or so (with some variation). That power
is too much to be delivered over the USB bus. The 3.5" drive
will come with its own power supply.
Example of a 3.5" external drive.
http://www.newegg.com/Product/ProductReview.aspx?Item=N82E16822148235
Neither of picture (1) or (2) puts any draw on the PC power supply at all.
In both those cases, there are hard drive failures noted. Since
drives are relatively cheap, I would buy two (different brands)
and put the files on *both* of them. There are too many horror
stories, where the only copy of data was on one of those external
drives. Having two drives, will help compensate for their
unreliability.
Paul
