External USB 2.0 case for 3.5" hard drive

  • Thread starter Thread starter Maximilian Michel
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Maximilian Michel

Hallo,

Did ever anybody see an external usb hard drive casing for 3.5" hard
drives without an external power supply?
I was only able to find cases with power supply via the usb-bus for
2.5" hard drives...

Cheers,

max
 
Maximilian Michel said:
Hallo,

Did ever anybody see an external usb hard drive casing for 3.5" hard
drives without an external power supply?
I was only able to find cases with power supply via the usb-bus for
2.5" hard drives...

Cheers,

max
Click to expand...
External 3.5 drives draw too much power, so can`t get it from the USB
port. This is why they need their own power supply.
bw..OJ
 
Maximilian Michel said:
Hallo,

Did ever anybody see an external usb hard drive casing for 3.5" hard
drives without an external power supply?
I was only able to find cases with power supply via the usb-bus for
2.5" hard drives...

Cheers,

max
Click to expand...

USB bus power is 5V @ 500ma AFAIK.

On a 2.5", only the starting power looks too high. The
running power numbers all look like they might fit in 2.5 watts.
Maybe a big capacitor inside the enclosure gives
enough energy storage, to start the drive without
flattening bus power ?

http://sdd.toshiba.com/main.aspx?Path=818200000c6f000000010000659c00002c78

A decent 3.5" drive probably takes 12 watts at idle.
That would be 5V@1A and [email protected], made by switching
conversion. That really needs external power, if you
were using USB.

Bus power on Firewire might be able to do it, at
12V and 1 amp. Firewire bus voltage can go higher
than 12V, in which case the current would be corresponding
lower to get the same power level. Active power on the
drive could be higher than 12W, and during spinup, the
power footprint is closer to 30W (2A on 12V to spin platter).
I don't know how high Firewire goes with regard to current
(there is only VP and VG after all, on those small connector
pins), so spinup might be what prevents Firewire from
being able to do the job.

So a reasonable expectation would be 2.5" storage via
bus power.

I just found a Firewire product and some comments on bus
powering. This outfit claims to be able to do some
3.5" bus powered stuff. I guess it just takes careful
disk selection (maybe something slower than 7200 rpm
in a 3.5" form factor). They use an energy storage
method, to get enough juice to handle spinup.

http://www.wiebetech.com/pressreleases/buspower.pdf

The only thing missing was solar panels and a hand crank :-)

Paul
 
All 3.5" enclosures require external power, like old jon said. However, some
include the power hardware within the enclosure, some have it on the power
cable.


Hallo,

Did ever anybody see an external usb hard drive casing for 3.5" hard
drives without an external power supply?
I was only able to find cases with power supply via the usb-bus for
2.5" hard drives...

Cheers,

max
 
USB bus power is 5V @ 500ma AFAIK.

On a 2.5", only the starting power looks too high. The
running power numbers all look like they might fit in 2.5 watts.
Maybe a big capacitor inside the enclosure gives
enough energy storage, to start the drive without
flattening bus power ?

http://sdd.toshiba.com/main.aspx?Path=818200000c6f000000010000659c00002c78
Click to expand...

I don't recall the exact figure but there is a clear limit
to the capacitance that can be non-isolated (effective for
starting a drive) on the USB bus. The limit is rather low,
something like 100uF or less. It's in the USB specs but I'm
too lazy to look it up ATM.
 
Hallo,

Did ever anybody see an external usb hard drive casing for 3.5" hard
drives without an external power supply?
I was only able to find cases with power supply via the usb-bus for
2.5" hard drives...
Click to expand...

3.5" drives use too much current to be bus-powered (at least
"normal" ones do, there might be something unusual but I'm
not aware of any). Typically the controller (bridge) board
itself would consume at least 30-80mA so you have even less
than the 500mA max available for the drive.

Therefore a supply is necessary, but it could be internal to
the enclosure or external power brick. The internal type
was more common on earlier corporate-grade gear like tape
drives or SCSI HDDs, and typically a IEC plug on the back
like on your system PSU. Naturally the internal PSU type
enclosure casings were quite a bit bigger, in general the
volume of such a supply was about 2/3 that of the drive
itself if it was of decent quality. They were also usually
metal, overall you'd be looking at a $200 class of product
rather than $40.
 
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