Powering a 2.5 inch hard drive adapter

[JimL]

While moving my XP system to a new 2.5 inch hard drive I used a USB adapter
that powered the drive off the USB. That's fine, but I'm wondering if it is
a good idea for regular use?

Thanks

 

[Guest]

While moving my XP system to a new 2.5 inch hard drive I used a USB adapter
that powered the drive off the USB. That's fine, but I'm wondering if it is
a good idea for regular use?

Thanks

USB ports are often protected by self-reseting PTC fuses.
If you look up the specs, you find that there are two.
The cold resistance before the first trip.
The cold resistance after it's tripped at least once.
The resistance is significantly higher once it's been tripped.
Running them hot degrades the PTC fuse.

That may explain why external hard drives work for a while, then
start complaining about excessive usb current.


I've addressed the problem four ways.
1) purchase only drive enclosures that have external power input.
2) cut the power wires on a usb extension cable and insert
external power.
3) The Bytecc BT-300 has a power socket right on the adapter.
By adding a jumper, you can run it powered by usb or the power brick.
The Bytecc has the additional advantage that it is capable of reading
the SMART data from a USB-connected drive.
4) Use a powered USB hub.

 

[Paul]

While moving my XP system to a new 2.5 inch hard drive I used a USB adapter
that powered the drive off the USB. That's fine, but I'm wondering if it is
a good idea for regular use?

Thanks

The USB port has a maximum power rating of 5V @ 500mA by design.
But how that power is monitored, varies by system.

On my desktop motherboards, a one amp Polyfuse is shared between
two USB connectors in the same USB stack. If I were to plug a
bus powered USB hard drive into one of those ports (but not
both at the same time), then chances are I'd have enough power
to run the drive.

On a laptop, they may use an 8 pin chip to police the power. Those
will cut off a load, much closer to the 5V @ 500mA limit. If
the drive does not work reliably on a laptop, then I would
either get a "two headed" USB cable (intended for this
application), or use a separate power adapter to power
the drive. Some drives have a small hole on the back,
that you plug a 5V wall adapter into.

2.5" hard drives vary in their power consumption. For
example, a 7200RPM drive might draw 1 amp for the first
ten seconds, while spinning up to 7200 RPM. You might experience
more powering difficulties, with a high performance 2.5" drive.

Paul

 

[JimL]

That can (assuming a properly designed and rated power
supply) work fine. It requires the PSU be supplying that 5V
to the USB port as clean power, and that it's of ample
capacity (if the USB port is powered by 5VSB rather than 5V
rail from the PSU, then when the system is turned off the
PSU fan turns off leaving the 5VSB circuit running hotter
than it does with the system running, but in this case you
might have the drive still running when the system is off
which seems undesirable).

Whether you can trust your PSU is providing clean output and
has ample capacity is the real question. In an ideal world
they all would, but in this world all PSU are not equal in
quality nor are all manufactureres rating then in a
standardized matter, not even considering the occasional
defects or failures a PSU might have.

Otherwise, internal power connectors and cabling are more
robust than that used on USB making it the more desirable
option when possible.

Thanks

 

[JimL]

The +5.0 power spec for a single USB2 port is 500ma, max.
Right now I'm looking at a 2.5" WD 500GB SATA drive,
(WD5000BEVT) which has a 5VDC power requirement of
0.55A, or 550ma. Also, the drive enclosure will require power.
The interesting thing is that I have a 350GB WD Passport
external 2.5" drive that uses a WD3500BEVT, with no issues
on a single USB port. If you are concerned, you can get a USB
Y cable, that connects to two USB ports on your PC.

Thanks

 

[JimL]

USB ports are often protected by self-reseting PTC fuses.
If you look up the specs, you find that there are two.
The cold resistance before the first trip.
The cold resistance after it's tripped at least once.
The resistance is significantly higher once it's been tripped.
Running them hot degrades the PTC fuse.

That may explain why external hard drives work for a while, then
start complaining about excessive usb current.


I've addressed the problem four ways.
1) purchase only drive enclosures that have external power input.
2) cut the power wires on a usb extension cable and insert
external power.
3) The Bytecc BT-300 has a power socket right on the adapter.
By adding a jumper, you can run it powered by usb or the power brick.
The Bytecc has the additional advantage that it is capable of reading the
SMART data from a USB-connected drive.
4) Use a powered USB hub.

Thanks

 

[JimL]

The USB port has a maximum power rating of 5V @ 500mA by design.
But how that power is monitored, varies by system.

On my desktop motherboards, a one amp Polyfuse is shared between
two USB connectors in the same USB stack. If I were to plug a
bus powered USB hard drive into one of those ports (but not
both at the same time), then chances are I'd have enough power
to run the drive.

On a laptop, they may use an 8 pin chip to police the power. Those
will cut off a load, much closer to the 5V @ 500mA limit. If
the drive does not work reliably on a laptop, then I would
either get a "two headed" USB cable (intended for this
application), or use a separate power adapter to power
the drive. Some drives have a small hole on the back,
that you plug a 5V wall adapter into.

2.5" hard drives vary in their power consumption. For
example, a 7200RPM drive might draw 1 amp for the first
ten seconds, while spinning up to 7200 RPM. You might experience
more powering difficulties, with a high performance 2.5" drive.

Paul

Thanks

 

[JimL]

the first time you have a dropout of a USB drive
and all data is gone, it is a stark reminder that USB is one
of the worst busses for data storage on a continual basis.

Perhaps this relates to another issue? When I got my new HD I put it into
the USB external to copy the system to it. After a little blood, sweat and
tears I booted to that new system and put the old one in the USB to copy
non-system partitions. That all worked and works fine, but...

Now, with that drive in the same place, NOTHING I have can even tell it is
there!

The new system doesn't see it. I have several disk utilities that don't see
it. I have a self-booting hard drive program on CD named DFSee. It is
scary powerful, reading and writing HD's at different levels with tests,
searches, cloning, imaging, data retrievals, saving and retrieving extra
MBR's, repairing file index errors, etc. It has routines written to correct
issues per the rules of several operating systems. IT says there is no HD
in the USB adapter.

It is set up the same as it was when I got the last two partitions off of
it - jumpered as slave. Nothing else to set up.

How can this be? Even a damaged drive shouldn't be invisible. I've tried
connecting it to all available USB ports with the same cable I used before
and it remains invisible. Do you think the adapter board smoked just as I
tried to access the drive the last time? Can some configuration of the
drive actually make it invisible?

Thanks

 

[JimL]

you can get a USB
Y cable, that connects to two USB ports on your PC.

Aha. That explains the cable that came with the 2.5 inch HD adapter. It
has USB A male connectors in all 3 places. One leg is 6 inches and one leg
is 24 inches.

Thanks

 

[JimL]

I failed to mention the other nasty problem with USB, that
if the OS is caching data, unplugging (intentionally or even
a momentary loss of connector contact) the drive can result
in complete corruption.

When a USB drive works, it works fine albeit at a slower
speed, but the first time you have a dropout of a USB drive
and all data is gone, it is a stark reminder that USB is one
of the worst busses for data storage on a continual basis.

Ignore my previous post. The drive works when I power it with the Y
connector cable.

Thanks