Maybe for *your* computer(s), but certainly not for mine.
The el-cheapo standby-type supplies that "Mercury" (rather charitably)
described as "Basic" offer only minimal "protection" against the simplest (and
rarest) types of total power failures, and little else. They can do
absolutely nothing about the (often abysmal) *quality* of the power coming out
your wall outlet. Hence, their ability to shield the load from the plethora
of short-term fluctuations (so-called "brownouts", noise, frequency and
waveform aberrations, etc.) that have become increasingly common as power
utilities scrimp ever more on their QOS (and chronically fail to ensure that
generating capacity keeps pace with demand) is sorely lacking. The worst of
them also often throw all sorts of self-generated noise onto the line (and
into the air), which can (and does) interfere with the operation of *other*
equipment (especially RF-based equipment, such as a wireless LAN -- or your TV
set).
...
Only by the marketing mavens trying to sell then to the Great Unwashed, and
the gullible fools who have bought into their line of bull.
...
This is flat-out wrong.
A proper double-conversion UPS will offer MANY advantages over the various
low-end pieces. Among these are effective isolation between the load and the
line, true sine-wave output with minimal THD (sometimes also provided by the
better line-interactive units, but definitely not by the low-end standby
supplies you claim above to be "more than sufficient"), more robust batteries
and inverters (they _have_to_ be beefier, as they are in use all the time as
opposed to "just occasionally") and usually better build quality in general.
As for cost... Well, that can (and will) be all over the map, depending on
the manufacturer, the vendor, and especially the load capacity. You can spend
a few hundred, or you can spend several thousand -- but this also applies, to
very nearly the same degree, to standby & line-interactive models. As I
stated in my earlier article, a proper double-conversion UPS will generally
cost something on the order of 1.5-2X what an equivalent line-interactive
model will run. Here are a few examples for units in the 1KVA range (which
would be quite adequate for the OP's application):
TRIPP LITE OMNI SMART 1050VA
(Line Interactive / Stepped-square output) $277.95
<
http://www.axiontech.com/prdt.php?item=34427&PRICECOMPARISONSID=7010b72b1aad24a0238d7ba547832d20>
TRIPP LITE SU1000XL
(Double Conversion / Sine-wave output) $413.95
<
http://www.axiontech.com/prdt.php?item=61114&PRICECOMPARISONSID=7010b72b1aad24a0238d7ba547832d20>
The latter is exactly 1.489296636086 times as expensive as the former.
Para Systems Minuteman SmartSine S1000
(Line Interactive / Sine-wave output) $325.
<
http://www.bisonbusiness.com/mis1fcoshcos.html>
Para Systems Minuteman MCP 1000 E
(Double Conversion / Sine-wave output) $525
<
http://www.bisonbusiness.com/mimcfcoshcou.html>
The latter is exactly 1.615384615385 times as expensive as the former.
And finally, both from <
http://www.battery-usa.com/Powercom-UPS.htm>:
PowerCom HOME-1000A
(Line Interactive / Sine-wave output) $281.33
PowerCom ULT-1000
(Double Conversion / Sine-wave output) $456.00
The latter is exactly 1.620872285217 times as expensive as the former.
Please note that I am *NOT* specifically recommending any of these particular
models, vendors, etc.; I'm just using them as handy examples.
...
You should take your own advice. Your description which follows is seriously
flawed in several ways (at least presuming you're talking about the typical
"switching" type PC power supply unit).
...
Maybe, but most often not. For the current to "pass through" a filter, that
filter must be composed (at least primarily) of inductive components (i.e., a
choke). But chokes are relatively expensive and bulky; and they don't do much
for you in a true AC environment. So typically, MOVs and bypass capacitors
are used instead. The current does not "pass through" these components (tho'
it might be said to "pass by" them).
...
Uhhh... no.
It is rectified, usually (or at least hopefully) by a full-wave bridge
rectifier circuit. This produces a (very rough and noisy) pseudo-DC output of
approximately 180V.
Virtually all noise, spikes, and surges are eliminated.
[snip]
Not even close!
Have you ever looked at the waveform output from one of those line-AC
rectifier circuits on a 'scope? I thought not. As noted above, at this stage
in the circuit, that waveform is *extremely* ragged and noisy (technically
referred to as "ripple") -- which is why the rectifier is (at least in any
half-decent supply) immediately followed up with more filtering caps (and
maybe even a small choke, this time, since the demands on it are so much less
after rectification).
...
It is disingenuous at best to call that a "layer of protection". It is simply
a necessary part any switching-type power supply. And the reasons for it are
not to provide any better protection or "power quality" to the load. The
near-sole reason for this type of design is *cost* -- you need a LOT less iron
to transform high-frequency (typically 5KHz to 50KHz) AC than low- (i.e.,
line-) frequency AC (60 Hz in the U.S.); and the cost savings provided by
using a relatively tiny transformer (see the next step in this saga) much more
than offset the costs of the "preliminary" rectification/switching circuitry.
It also makes for a physically smaller and lighter PSU, which saves still more
money in manufacturing and shipping costs down the line.
...
A transformer has *nothing* to do with "galvanic isolation", at least in this
context. And "galvanic isolation" in turn has *nothing* to do with protecting
a PC from power-line anomalies.
Do you even know what that term means? (Hint: Think corrosion. Or
batteries.)
...
Again, a simple rectifier circuit, which again produces a very rough and noisy
pseudo-DC output -- actually, several such rectifiers, producing several such
outputs, since the transformers used in PC PSUs necessarily have multiple
secondary windings/taps.
...
Well, of course -- we've just made a ton of noise and other crap via the
rectification process, which we now need to dispose of. But this is S.O.P.
for *any* power supply, switching or linear, in a PC application or virtually
anything else.
...
Uhhh... No, again. You are presumably referring to active voltage
regulation, which any decent PSU (for virtually any application, not just PCs)
will provide. But this is (at least typically) not so much a matter of
"overvoltage protection" (or under-voltage, for that matter) as it is a means
of enabling the designer to scrimp on the final filtering caps and/or chokes.
With an adequately responsive AVR circuit to rely on, those filtering caps
and/or chokes don't need to be nearly as effective as would be necessary if
they were being counted on to provide *all* of the output filtering; hence,
they can be smaller and cheaper.
In reality, the actual "over-voltage protection" feature provided by some PC
PSUs works *against* data integrity, not for it, since it can (and will,
if/when it trips) arbitrarily shut down the PSU (requiring a AC-off cold
start) without warning.
...
Thirty years ago, the "PC" had not yet been invented (tho' the first 8-bit
microprocessors had been developed, so the birth of the PC was imminent -- I
discount such "lunatic fringe" aberrations as the MITS Altair, which was
purely a hobbyist piece -- with a *linear* power supply, by the way), and
switching power supplies (in any application) were both relatively rare and
quite crude by today's standards. They were, quite justifiably, viewed as
rot-got el-cheapo substitutes for a "proper" linear power supply.
Yes, today's switching PSUs (at least the higher-quality ones) are much better
than those early travesties; but that's not the point.
...
Nonsense.
*IF* we could count on both the quality and the reliability of the AC mains
power we use to feed these supplies, at least most of them would do an
admirable job of running the mobos, memory, CPUs, disk drives, etc., that your
typical PC is composed of. But we *cannot* count on that. In fact, that
situation is getting worse every day, for the reasons already touched on above
(blame the NIMBYs, if you want; but the fact remains -- we are facing an
electrical power crisis that will surely only get worse before it gets
better). Concurrently, we are becoming more and more dependant on our
electronics -- especially our computer systems -- for our day-to-day
activities and existence. That is a prescription for a very unpleasant
wake-up call, which we *will* get, sooner or later; but I digress.
Getting back to the point...
The "hold-up time" specs quoted for typical PC PSUs range from about 10ms to
perhaps 17ms -- i.e., one AC cycle _at_best_ -- and even these are "best case"
specs obtained under laboratory conditions. All manner of power-line
aberrations (besides simple "total failures") will have event durations which
exceed this threshold. So some sort of "upstream" protection is
near-mandatory, if you value your data.
The "switching time" specs for typical low-end standby-type "UPS"s are in the
several-millisecond range (tho' again, these are "best case" lab-conditions
specs). Now, you might think that, because these figures are significantly
lower than (typically about 1/4 - 1/2) the typical PSU "hold-up time", there's
no problem... But you'd be wrong. This is only the actual *switching* time,
which by definition only starts *after* a power-line disruption has been
sensed and the control circuit tripped -- IOW, by the time the "UPS" *starts*
to switch the load, the crap has *already* been fed through to the output.
...
Ah, ha! Perhaps this explains (at least in part) your apparent fundamental
misunderstanding of the issues. It's not about "protection of computer
components", all of which are virtually always easily replaceable. It *is*
about protection of your DATA -- which in any serious application is far more
valuable than all the hardware, software, peripherals, etc., put together.
...
But here you imply that any ol' "plug-in UPS" is equivalent to any other
"plug-in UPS" -- which is most assuredly *NOT* the case. (And BTW... You're
also dead wrong about blackouts/brownouts not being able to harm hardware; and
I have the fried A/V gear from both my shore home and my main residence to
prove it.)
This raises the question of just what axe you're attempting to grind.
Out of curiosity, I just took a quick look at some of your other recent
postings via Google Groups; and I must say... Your grossly simplistic (and in
some cases just-plain-wrong -- such as was exemplified in
<
http://groups.google.co.uk/[email protected]>;
hint: the voltage output of a regulated power supply will hold up just fine
until *immediately* before it falls apart spectacularly -- hence, your "cure
all" DMM tells you NOTHING about reserve capacity) views on matters related to
power supplies and your apparent obsession with PSUs as the root cause of all
computer problems (even those rather obviously caused by software or "pilot
error") seems suspect, at best.
No one here (least of all me) is claiming that a (presumably decent-quality)
switching-type standby "UPS" is totally worthless; but to suggest that they
are the end-all and be-all of UPS design is both misleading and just plain
silly.
--
Jay T. Blocksom
--------------------------------
Appropriate Technology, Inc.
usenet02[at]appropriate-tech.net
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
-- Benjamin Franklin, Historical Review of Pennsylvania, 1759.
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