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From: Arno on 9 Apr 2010 18:56
Al Dykes <adykes(a)panix.com> wrote:
> In article <8291rtFlahU1(a)mid.individual.net>, Arno <me(a)privacy.net> wrote:
>>Al Dykes <adykes(a)panix.com> wrote:
>>
>>> I don't have a high opinion of an external USB disk powered by a
>>> wall-wart as industrial-strength kit. Having the PC powered on a UPS
>>> and the Wall wart on house power has potential problems, IMO.
>>
>>The wall-type PSUs are electrically insulated, there should not
>>be a problem, except perhaps aestetically.

> They are also made by the lowest bidder. Of course, plugging one into
> a UPS doesn't change that.

Yes. But the insulation requirement ensures that you do not get
ground loops or current over ground.

>>> What are the thoughts of putting retail external USB disks on
>>> entry-level UPS systems? These systems are stepped-sine power and
>>> they don't specify switch-over time.
>>
>>To what end? It should work, but it only makes sense if you
>>have the PC on an UPS as well. Also take care to use the
>>VA rating (V * A as stated on the plug), as switching power
>>plugs may not have power factor correction.

> Voltage differentials, ground loops?

No ground loops with the standard wall plugs. Voltage differential
is not a problem with wide-input ones. With heavy transformer types
it should not be an issue either, but they are less resilient.

Arno
--
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name
GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
----
Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
From: William R. Walsh on 16 Apr 2010 00:30
Hi!

> I don't have a high opinion of an external USB disk powered by a
> wall-wart as industrial-strength kit. Having the PC powered on a UPS
> and the Wall wart on house power has potential problems, IMO.

The included power supplies are almost invariably the switchmode type. Some
put out both voltages required by the drive and bridge board (5V/12V) while
others only put out straight +12VDC and let a DC-DC converter in the
enclosure produce +5VDC.

The wall wart is almost always a switchmode power supply--cheap,
lightweight, easily able to handle wide ranges of input voltages and
reliable if properly made. Most seem to output about 2 amps, and good ones
don't get all that hot (suggesting that they ought to live a long time).

> What are the thoughts of putting retail external USB disks on
> entry-level UPS systems? These systems are stepped-sine power and
> they don't specify switch-over time.

I've had no problems. I have a setup with the disks on one UPS and the
computer on another. Both UPS units are cheap APC "plugstrips", each one
about five years old. One is on its second battery. Both are plugged into
the same duplex outlet, on the same circuit.

William


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