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Observations on a UPS - follow up to a previous post



 
 
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  #21  
Old August 13th 07, 03:57 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
Michael A. Terrell
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Posts: 332
Default Observations on a UPS - follow up to a previous post

Arfa Daily wrote:

But that's my point. You can't have a 'true' sine-based RMS figure for power
consumers that draw a pulsed current. Just because it is a sine wave that's
*available*, it doesn't mean that the load will draw anything like a
sinusoidal current, from it. The only items that will are those that are
totally 'passive' in nature, such as light bulbs. Even power supplies that
are transformer based, are likely to draw current in pulses from the
available sinusoidal supply, and switch mode power supplies, on which most
modern consumer electronics are based, most certainly won't draw a
sinusoidal current from the supply.

Arfa



ICs to do the true RMS conversion are dirt cheap these days.


http://www.analog.com/library/analogDialogue/archives/34-01/rmsarticle/index.html

http://www.analog.com/en/subCat/0,2879,773%255F866%255F0%255F%255F0%255F,00.html
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prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
  #22  
Old August 13th 07, 04:22 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
Arny Krueger
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Default Observations on a UPS - follow up to a previous post

"David" wrote in message
et

I have a "Kill-A-Watt" and it appears to display true RMS
for voltage and current readings. The voltage reading for
a modified sine wave from a standard UPS displays the
actual RMS voltage.


It is speced to deliver true RMS readings. It will also display power
factor.

I do not know what crest factor it
can handle


Can't find it in the manufacturer's detailed specs.

but displays power factors of considerably
less than unity for most consumer electronics with DC
rectifiers off of the line voltage. It is a very nice
unit for the price.


Agreed.


  #23  
Old August 13th 07, 05:25 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
kony
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Posts: 7,416
Default Observations on a UPS - follow up to a previous post

On Mon, 13 Aug 2007 04:42:02 -0700, "William Sommerwerck"
wrote:

Lead-acid batteries (like is [sic!] in your car) have major issues
if they are completely drained, these are also the common battery
in cheap, well, just about everything.


The _only_ consumer products I've owned that used lead-acid batteries were
an early Sony Discman, and two APC SPSs. They are not common in consumer
products. They provide relatively high capacity at a low cost (which is why
they're used in SPSs and UPSs), but they are too-easily damaged by a full
discarge. I accidentally ruined a $45 batter for the Sony D-T10.



Practically all consumer grade UPS use lead-acid batteries.
Other common items using lead-acid batteries are some of the
handheld halogen spotlight (flashlights), and automotive
portable power station "thing-a-majigs" like those that can
jump a car or have a flashlight/pump/inverter. A few
transportation devices have them also like a kid's motorized
big-wheels or skateboard or motorized bike, etc.

Any decently designed UPS will cut off power before the lead
acide battery is drained to a critical level, although it is
still much harder on the battery to drain to any significant
extent, a large % of total capacity instead of the UPS
turning off as soon as possible.
  #24  
Old August 13th 07, 05:32 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
kony
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Posts: 7,416
Default Observations on a UPS - follow up to a previous post

On 13 Aug 2007 01:07:28 GMT, Arno Wagner
wrote:

In comp.sys.ibm.pc.hardware.misc Doc wrote:
Recently I asked about suggestions regarding a UPS. I ended up
getting an 875 VA 525 Watt "Geek Squad" model from Best Buy - yeah,
yeah, everyone says Geek Squad stuff is overhyped junk, but at $69 on
sale, the price seemed right.


The price is all wrong. Nobody can build a decent product with
these specs for that price. You cannot even buy the components
needed in decent quality for that price.


Depending on your definition of "decent", this may be true,
but it's going to be roughly equivalent to what you'd buy
from APC as a 500VA for about $50 so if that's what the
budget allows, it's not an exceptionally low price (also
considering you can sometimes get the APC discounted or with
rebate putting it closer to $20-30 than to $50.


It seems to handle my 2 computers fine - a PIV 2.4 gig and a PIII 933
mhz sharing a monitor. With both machines and the monitor on, the
onboard readout shows them well below the unit's max capacity, drawing
about .250 - .260 kw (which I assume translates to 250 - 260 watts) ,
with an estimated run time of 9 minutes with both computers. More than
enough to get me through short hit outages with both machines running.


And with the el-cheapo battery in there, that figure will be down to
1 minute in no time. And you would be well advised to test the
claim. Software can be made to lie to you, you know.


There's no reason to belive the battery is especially cheap,
it's going to be a standard lead-acid which is quite a
mature technology today, a commodity item essentially and
all that's really at question is whether the manufacturer
conservatively rated the unit or if it's unlikely to meet
the specs due to design budget constructions. Either way,
it's probably $70-100 worth of UPS, it will likely do as
well as anything else available for the same price.

If one were to pay = 2X as much, naturally the expectation
would be it's either fancier or higher capacity or an online
type, etc, but there is no expectation the battery is
inherantly any higher quality per se, though probably higher
capacity due to being a larger size or a series of two
batteries.
  #25  
Old August 13th 07, 05:41 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
Richard Crowley[_2_]
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Posts: 33
Default Observations on a UPS - follow up to a previous post

"James Sweet" wrote ...
"Doc" wrote...
Maybe, but a lot of people seem to swear by the Kill-A-Watt meter,
which can be had all day for around $25 online, eBay etc.


EE friend of mine compared one to a $2500 power analyzer at work, found
that the Kill A Watt performance is pretty much inline with the specs
printed for it. It's not as good as the professional equipment, but it's
really very impressive for what it is and certainly adequate for consumer
use. The wonders of modern microelectronics, it's amazing what they can do
with one inexpensive chip and a handfull of passive components. I still
remember when a pocket calculator was $300, then a few years later $50
would buy one just as effective, and not long after that they were under
$20 and those are all more capable than large machines costing many
thousands just a few decades earlier.


Agree completely. They are great when used with the regular
sine-wave mains power grid. However note that many have
been fried beyond repair when used with any kind of square-
wave source: inverter, UPS, etc. even "stepped sine" waveforms.

The problem appears to be the capacitive voltage divider used
to power the Kill-A-Watt electronics. The high frequency harmonics
deliver way too much power to the shunt regulator through the
capacitor and something fries.


  #26  
Old August 13th 07, 06:55 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
CBFalconer
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Posts: 919
Default Observations on a UPS - follow up to a previous post

Doc wrote:
"William Sommerwerck" wrote:

My experience -- at least where I live -- is that the power is
off for a fraction of a second, or hours. There's rarely anything
in-between.


In general, I'd say that's my seat of the pants impression too,
though not always. I also notice they'll often come in clusters.

The transformer - if that's the correct term for it - big gray
basically cylindrical unit on top of a power pole - near my house
blew once. Powerful **BOOM** and a huge column of flame. Not sure
what the fuel for the flame was, do they have oil in them? Also a
bit disconcerting since anyone nearby surely would have been in
jeopardy from flaming debris.

Needless to say, power was out for a while on that one.


About 30 years ago a friend of mine was in a neighborhood where
multiple houses were supplied from one undersized transformer, and
the power company just ignored all requests to replace it. The
residents got together, and all turned on air-conditioners, ovens,
whatever, and then went outside to watch the transformer blow. It
did, and the scheme produced a new proper sized transformer.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
http://cbfalconer.home.att.net



--
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  #27  
Old August 13th 07, 07:07 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
Arfa Daily
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Posts: 49
Default Observations on a UPS - follow up to a previous post


"David" wrote in message
. net...

"Arfa Daily" wrote in message
...

"David" wrote in message
et...

But be aware that in general, these cheap 'power' meters are expecting
'traditional' sine-draw loads. I have seen wildly inaccurate standby
figures being given for equipment, by eco-campaigners that have been
let loose with one. A lot of modern equipment that makes use of switch
mode power supplies, handles standby mode by brief bursts of full draw
operation. This can confuse a simple power calculating algorithm that's
expecting continuous draw. Also, the draw by many cheapo switchers is
very asymmetric and 'dirty', and may also not produce a true reading.

I wouldn't connect a UPS to a fridge. These things are notorious for
pulling a short-term startup current of tens of amps, as they get the
compressor turning over. The UPS would probably fall over before being
able to supply this, and might, as someone else suggested, even sustain
damage.

Arfa
I have a "Kill-A-Watt" and it appears to display true RMS for voltage
and current readings. The voltage reading for a modified sine wave from
a standard UPS displays the actual RMS voltage. I do not know what crest
factor it can handle but displays power factors of considerably less
than unity for most consumer electronics with DC rectifiers off of the
line voltage. It is a very nice unit for the price.

David


But that's my point. You can't have a 'true' sine-based RMS figure for
power consumers that draw a pulsed current. Just because it is a sine
wave that's *available*, it doesn't mean that the load will draw anything
like a sinusoidal current, from it. The only items that will are those
that are totally 'passive' in nature, such as light bulbs. Even power
supplies that are transformer based, are likely to draw current in pulses
from the available sinusoidal supply, and switch mode power supplies, on
which most modern consumer electronics are based, most certainly won't
draw a sinusoidal current from the supply.

Arfa

Arfa,
I know that the current draw on these things is anything but sinusoidal.
My point was that the "Kill-A-Watt" seems to actually compute the RMS
value for that complex current waveform as well as non-sinusoidal voltage
waveforms.

David


OK. I'm not sure that 'RMS' is the right term to attach to any value derived
from a ragged-arsed waveform, as it is a mathematical function normally
associated with symetrical waveforms, which the draw by a SMPS may very well
not be, but I see what you're saying.

What I am trying to say is that a chip which is designed to produce an RMS
reading from a sine wave, may well produce a meaningful figure from a
non-sinusoidal waveform also, but *only* if it is still symetrical.

Arfa


  #28  
Old August 13th 07, 07:18 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
Matt Ion
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Posts: 41
Default Observations on a UPS - follow up to a previous post

Doc wrote:
On Aug 12, 8:45 pm, "William Sommerwerck"
wrote:

My experience -- at least where I live -- is that the power is off for a
fraction of a second, or hours. There's rarely anything in-between.



In general, I'd say that's my seat of the pants impression too, though
not always. I also notice they'll often come in clusters.

The transformer - if that's the correct term for it - big gray
basically cylindrical unit on top of a power pole - near my house blew
once. Powerful **BOOM** and a huge column of flame. Not sure what the
fuel for the flame was, do they have oil in them? Also a bit
disconcerting since anyone nearby surely would have been in jeopardy
from flaming debris.

Needless to say, power was out for a while on that one.


TRMOAS (that reminds me of a story)...

Years ago, when Atari ST computers were common, friends of mine lived in
and old house with just such a transformer on the adjacent pole.
Buddy had been trying for ages to get his girlfriend to start learning
to use the computer, but she was always afraid she'd "break something".

Finally one day, he convinced her to sit down and give it a try. She
took a deep breath, put her hands on the keyboard... as the room was lit
up by a brilliant flash through the window, shaken by a magnificent
**BOOM!**, and the computer screen went black.

Poor girl was in a complete panic, she was SURE it was her fault...

As it turned out, a drunk speeding down the road outside in his van had
gone THROUGH two nearby power poles and finally stopped just shy of
hitting a third; the first impact brought the lines down and was
sufficient to explode the transformer just outside their window.

....took her years to ever touch a computer again
  #29  
Old August 13th 07, 09:03 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
CBFalconer
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Posts: 919
Default Observations on a UPS - follow up to a previous post

Arfa Daily wrote:

.... snip ...

OK. I'm not sure that 'RMS' is the right term to attach to any
value derived from a ragged-arsed waveform, as it is a mathematical
function normally associated with symetrical waveforms, which the
draw by a SMPS may very well not be, but I see what you're saying.

What I am trying to say is that a chip which is designed to produce
an RMS reading from a sine wave, may well produce a meaningful
figure from a non-sinusoidal waveform also, but *only* if it is
still symetrical.


Oh? Try a square wave, for example. Nice and symetrical. You are
over-simplifying.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
http://cbfalconer.home.att.net



--
Posted via a free Usenet account from http://www.teranews.com

  #30  
Old August 13th 07, 09:11 PM posted to comp.sys.ibm.pc.hardware.misc,alt.comp.hardware,rec.audio.pro,rec.video.desktop,sci.electronics.repair
Arny Krueger
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Posts: 36
Default Observations on a UPS - follow up to a previous post

"Richard Crowley" wrote in message

"James Sweet" wrote ...
"Doc" wrote...
Maybe, but a lot of people seem to swear by the
Kill-A-Watt meter, which can be had all day for around
$25 online, eBay etc.


EE friend of mine compared one to a $2500 power analyzer
at work, found that the Kill A Watt performance is
pretty much inline with the specs printed for it. It's
not as good as the professional equipment, but it's
really very impressive for what it is and certainly
adequate for consumer use. The wonders of modern
microelectronics, it's amazing what they can do with one
inexpensive chip and a handfull of passive components. I
still remember when a pocket calculator was $300, then a
few years later $50 would buy one just as effective, and
not long after that they were under $20 and those are
all more capable than large machines costing many
thousands just a few decades earlier.


Yup. I logged lots of hours on mechanical calculators, Wang shared-logic
desk calculators, and the HP35.

Agree completely. They are great when used with the
regular sine-wave mains power grid. However note that
many have been fried beyond repair when used with any kind of
square- wave source: inverter, UPS, etc. even "stepped sine"
waveforms.


News to me. I've used mine with UPSs, but the application was not long-term
use.

The problem appears to be the capacitive voltage divider
used to power the Kill-A-Watt electronics. The high frequency
harmonics deliver way too much power to the shunt
regulator through the capacitor and something fries.


You're aware that capacitive voltage dividers have flat frequency response,
right?


 




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