3.5" HDD enclosure. How much power really?

  • Thread starter Thread starter Noozer
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Noozer

I've got several USB 3.5" HDD enclosures that I move between, depending on
what I'm doing with my computer. It's a bit of a nuisance having to move the
power cord between the drives.

The PSU for the enclosure is marked as providing 1.5amps of 5V and 1.5amps
of 12v. How much of this is really needed?
 
Noozer said:
I've got several USB 3.5" HDD enclosures that I move between, depending on
what I'm doing with my computer. It's a bit of a nuisance having to move the
power cord between the drives.

The PSU for the enclosure is marked as providing 1.5amps of 5V and 1.5amps
of 12v. How much of this is really needed?
Click to expand...

You can check the actual hard drive spec on the hard drive
manufacturer's
web site.

Typical numbers I use for estimation purposes are 5V @ 1A and
12V @ 0.6A or so. But the spinup current, for the first 10 seconds, is
higher on the +12V rail. Many drives draw 12V @ 2.0A for the first
10 seconds, and I did see one spec that listed 12V @ 2.5A for the
first 10 seconds. So while your power source is well matched for normal
operation of a single drive, the supply may cause the drive to either
spin up slowly, or it could be that the power supply has a surge spec
that takes spinup into account (i.e. allows 2 or 2.5A to be drawn
for 10 seconds). If the power source fails to take spinup into
account, the power source could even detect the load as an abnormal
condition, and shut down.

At one time, the "standard footprint" for hard drive power, was 30W or
40W (40W for some of the hotter SCSI drives). Enclosures came with
either a 30W or a 40W internal supply. Taking spinup into account,
a 30W footprint still seems to be appropriate for modern drives. A
pleasant
exception is laptop drives that only use +5V and draw a max of 5V @ 1A.
But they don't have the same level of performance as a real desktop
drive.

Paul
 
Paul said:
You can check the actual hard drive spec on the hard drive
manufacturer's
web site.
Click to expand...

Actually, I looked at the spec sheets at Maxtor and Seagate and it doesn't
mention anything about power requirements. Now, I didn't dig too much, but
when you pick a drive model and click the "specs" link, that's where I'd
expect to find them.
Typical numbers I use for estimation purposes are 5V @ 1A and
12V @ 0.6A or so. But the spinup current, for the first 10 seconds, is
higher on the +12V rail. Many drives draw 12V @ 2.0A for the first
10 seconds, and I did see one spec that listed 12V @ 2.5A for the
first 10 seconds. So while your power source is well matched for normal
operation of a single drive, the supply may cause the drive to either
spin up slowly, or it could be that the power supply has a surge spec
that takes spinup into account (i.e. allows 2 or 2.5A to be drawn
for 10 seconds). If the power source fails to take spinup into
account, the power source could even detect the load as an abnormal
condition, and shut down.
Click to expand...

Ouch! I didn't realize that drives pulled so much power.

I was hoping to find a hefty power supply and just daisy chain a number of
drives. That way I could just power on the one(s) that I wanted to use at
that time without mucking around with cables.
exception is laptop drives that only use +5V and draw a max of 5V @ 1A.
But they don't have the same level of performance as a real desktop
drive.
Click to expand...

Ya... It's nice when you can run a 2.5 enclosure straight from a USB port.
 
Actually, I looked at the spec sheets at Maxtor and Seagate and it doesn't
mention anything about power requirements. Now, I didn't dig too much, but
when you pick a drive model and click the "specs" link, that's where I'd
expect to find them.
Click to expand...

Look on the drive label. Taking one new Maxtor for example
(Diamondmax 10, 6L100P0, 100GB), it's listed as

5V - 740mA, 12V - 1500mA

The 12V current is unusually high, significantly higher than
most 7K2 RPM drives I've seen, leading me to suspect this
figure is not directly comparable to other drives- maybe it
is the peak spin-up current or some kind of (n)second
average for spinup, rather than regular operating current.



I was hoping to find a hefty power supply and just daisy chain a number of
drives. That way I could just power on the one(s) that I wanted to use at
that time without mucking around with cables.
Click to expand...

You can do that, and the most cost effective PSU would
probably be an ATX for a computer because if it being such a
commodity item. IOW, a 250-300W ATX PSU is likely to cost
less than a 100W 5V+12V generic (nonspecific) industrial
switcher, and will have the drive connectors on it already
too, saving addt'l cost and time.

Of course you will need a power switch between PS-On and
ground on the PSU leads, or you could just use an old AT
supply, though if it's quite old it might not be in the best
shape anymore, fan or caps might be drying out.
 
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