GKW said:
I recently purchased a portable external hard drive. It's a USB powered
drive. When I plug it into my laptop and try to copy something to it, I get a
dialogue box that says "Power Surge On Hub Port, A USB device has
malfunctioned and exceeded the power limits of it's hub port. You should
disconnect the device"
What causes this? I don't think there is anything wrong with the drive
because this is the 2nd one of these that I have had this happen with. I
though about switching to a portable external hard drive by another
manufacturer
There is a solution for this, but it isn't a very satisfying one.
(By that I mean, it probably works most of the time, but I
wouldn't want to power something that needs a whole 1 ampere of
current with it.)
http://secure.serverlab.net/shop/graphics/00000001/yCable.jpg
That cable has two connectors on one end of the cable. One connector only
uses the power pins, while the second is a full USB connector.
The two connectors go into the computer USB jacks. The connector
on the right, is a small square USB one, that would plug into
the hard drive enclosure. (If the enclosure doesn't have a
removable USB cable, then this won't work.)
(computer (small square end
end) Plugs to the drive)
+5V -----------------------+---- +5V
Data+ ------------> Data+ |
Data- ------------> Data- |
GND ---------+----- GND |
| |
| |
GND ---------+ |
(none) |
(none) |
+5V -----------------------+
The basic idea, is the power output of two USB ports is combined.
A single USB port, has a limitation of 5V @ 500mA. That is a total
of 2.5W. Some 2.5" hard drives, when they're spinning at their
normal speed, need less power than that. But the 10 second interval,
where the drive starts from zero RPM, and the platter spins up, that
takes more energy. On some drives, it might take double the power,
for the first ten seconds. (On, say, a 7200RPM 2.5" hard drive.)
Inside the laptop, there are a couple options for power handling.
The lazy way, is to use a simple Polyfuse, and use a single fuse to
protect two USB connectors in one stack.
USB1 ---+------ Polyfuse ----- +5V inside laptop
USB2 ---+ 1.1 amps
Now, if that is the way they did it, then you likely wouldn't
have had a problem at all.
There is another way to do it, involving "precision policeman"
chips. These monitor current consumption on each port, and cut
off the port if more than 500mA is drawn.
USB1 -------- current_monitor ------- +5V inside laptop
USB2 -------- current_monitor ------- +5V inside laptop
If you were to get one of those "two headed" or "USB Y cables",
then one small issue, is the electricity doesn't know which
of the two cable heads to flow down. It is possible for the
cables to "current hog", and one connector might still draw
the majority of power. I don't know how the cable designer
can ascertain that all customers will be satisfied by the
usage of the cable. There isn't enough voltage drop budget
in the USB standard, to go sticking resistance in the path,
to even up the current flow and get closer to an even split
on each cable. There are some active power methods (i.e.
placing a switching regulator in the circuit), that could guarantee
a fix, but that would cost money. As far as I know, the cable
scheme above is a "dumb" one, without circuits inside the cable.
The external hard drive may have provision for a separate adapter input
(barrel connector input on the shell of the enclosure). If so,
you could purchase the optional adapter, and plug that into
the drive. That means you have to be near an A.C. power source,
when you want to use the external USB drive.
If you purchase one of those USB Y-cable things, then it should
do the job, and still allow a portable solution. As long as the
drive is not drawing more power than such a crude solution
can provide, without tripping the laptop "current surge"
detection.
Example of a cable for sale here.
http://www.amazon.com/Cables-Go-Y-C...1?ie=UTF8&s=electronics&qid=1216527014&sr=8-1
HTH,
Paul
