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.

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.


Interesting, well mine is the 240V UK version which I got back before I
found them offered here but from looking at the buttons and display it's
obviously the same unit as the Kill A Watt. At any rate I've tested it and
it works well all the way down to 60VAC, and frequencies from 30 Hz all the
way up to nearly 400Hz where the readings start to get screwy. I've run it
off inverters, used an adapter to hook it up to my 240V central heat pump to
measure that, it's taken everything I've tossed at it and so far keeps
working.

On Aug 13, 7:38 am, Arno Wagner wrote:

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.

Ugh. Putting them up for each individual hous is a very, very
historic way to do it.


I don't think there's one by every house, seems like you see them
every few poles.


The right way to do this is to use bigger transformesr for 10-100 houese
and to bury 3-phase AC lines. A lot more expensive, but pays off
in the long run, since you have less problems. And all these ugly
poles and transformers will vanish.


I know the power lines coming into my house are definitely above
ground. They're strapped to a supporting cable coming from a power
pole.

On Aug 13, 12:32 pm, kony wrote:

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.


FWIW, I was in that same Best Buy today and the UPS model I got for
$69 was back to its normal price of $119.

Ugh. Putting them up for each individual hous is a very, very
historic way to do it.


I don't think there's one by every house, seems like you see them
every few poles.


Generally it's 4-10 houses per transformer, it's nice, it makes it possible
to have quite good voltage regulation. I rarely see mine change by more than
a volt plus or minus.


The right way to do this is to use bigger transformesr for 10-100 houese
and to bury 3-phase AC lines. A lot more expensive, but pays off
in the long run, since you have less problems. And all these ugly
poles and transformers will vanish.



I'd love to have 3 phase, I've never seen it in a residence though, and
residential equipment is all single phase anyway, it works.

I kinda like above ground power, at least for the big stuff. Most of the
houses around here from the late 70s on have underground power, but some of
the old lines are starting to deteriorate so they've had to dig up streets
and flower beds to replace them.

"James Sweet" wrote in message
news:ZQawi.3100$hK5.368@trndny02...


Ugh. Putting them up for each individual hous is a very, very
historic way to do it.


I don't think there's one by every house, seems like you see them
every few poles.


Generally it's 4-10 houses per transformer, it's nice, it makes it
possible to have quite good voltage regulation. I rarely see mine change
by more than a volt plus or minus.


The right way to do this is to use bigger transformesr for 10-100 houese
and to bury 3-phase AC lines. A lot more expensive, but pays off
in the long run, since you have less problems. And all these ugly
poles and transformers will vanish.



I'd love to have 3 phase, I've never seen it in a residence though, and
residential equipment is all single phase anyway, it works.

I kinda like above ground power, at least for the big stuff. Most of the
houses around here from the late 70s on have underground power, but some
of the old lines are starting to deteriorate so they've had to dig up
streets and flower beds to replace them.


Isn't the 'high' voltage that you have in the US for powering washing
machines and the like, phase to phase ? Seems like it wouldn't be that hard
for the power company to put in the third phase as well ? (I might be
totally adrift on this one - I'm not a power engineer ;-) )

Arfa

"William Sommerwerck" wrote in message
...
So are you saying that a meter that measures *true* RMS
anything -- power, current, volts -- will do so correctly even
if the waveform is asymmetric about the zero point? I always
believed that an even distribution about the zero point was a
requirement for an accurate representation of an RMS value.

The RMS value of a waveform has nothing to do with the shape or symmetry
of
the waveform.

Assuming the meter is correctly designed, yes. RMS has a clear, specific
definition, and if the measurement is correctly implemented, the reading
will be correct.

Two qualifications... If the waveform is non-periodic, the measured RMS
value will vary according to the sample period. Also, if the waveform
includes a DC component, and the meter blocks it with a capacitor, then
the
RMS reading will not include the DC component.


Ah, OK. Perhaps it's non-periodicity that I'm getting confused with. As I
say, college seems a long-haired good music time ago now ...

Arfa

On Aug 12, 10:24 pm, "James Sweet" wrote:


Yeah CRT monitors take a lot of juice, it's one of the reasons flat panels
are so popular, though I still prefer a good CRT as it looks slightly better
to my eyes.


I don't like the way LCD/flat panel monitors look. The image isn't as
sharp and loses brightness unless you're sitting dead-center in front
of them, even the models that supposedly have a wider viewing angle.

In comp.sys.ibm.pc.hardware.misc James Sweet wrote:


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.

Hmm. Interesting. I trust he did this right and tested non-ohmic
loads such as a PC PSU as well?



Yes, of course, pure resistive loads can be measured just fine with a
multimeter. We were interested primarily in using it to measure discharge
lamp systems in which the power factor and current waveforms can be all over
the place and vary greatly with the state and condition of the lamp. If the
meter wasn't able to handle odd waveforms, the power factor measurement
function would be useless, but it works pretty well, accuracy is within
about 2% on the sample tested.



Good to know, so it _can_ be done relatively cheaply today.

Arno

"James Sweet" wrote in message
news:ZQawi.3100$hK5.368@trndny02

I'd love to have 3 phase, I've never seen it in a
residence though, and residential equipment is all single
phase anyway, it works.

The German town I lived in during the late 70s had something like 440/3
phase which was used for the water heater. Obviously, it would work wonders
with motors.

As you no doubt know synchronous motors are the big thrill for 3 phase.

We seem to be making an end run on the issue by running DC motors through
transformerless AC-powered intelligent controllers.

I kinda like above ground power, at least for the big
stuff.

Interesting, because a lot of big stuff around here is underground until it
hits the neighborhood pole transformers. IOW, the next regional substation
up has all its ins and outs underground. Underground lines run to the
neighborhoods. They feed strings of poles in people's back yards.

Some people such as myself have converted their house feed to underground,
but it is pretty rare around here.

My application is peculiar - I live on a corner lot with a very narrow back
yard and lotsa trees. Also, my previouis above-ground drop was never code
and eventually failed. The part of the house where the power entry was no
longer exists.

Above-ground feed to the house was ugly no matter how it was done. The
utility's pricing scheme made the conversion to underground very
economically attractive, because my house needed a minimal length feed.
Their marketing people made up a price list with minimal initial costs and
buried most people's installation fees in the per-foot charge. I got quite
a bit of hardware and labor for my $250.

I hear that some utilities will convert people for free in some
neighborhoods.

Most of the houses around here from the late 70s
on have underground power, but some of the old lines are
starting to deteriorate so they've had to dig up streets
and flower beds to replace them.

Our neighborhood was built up from 1930 to 1955, so everything is above
ground. I've seen individual home conversions, but nothing on a neighborhood
scale.

"Richard Crowley" wrote in message

"Arny Krueger" wrote ...

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

Perhaps you are not aware that many inexpensive consumer
mains power supplies use a capacitor rather than a
resistor as the series element of a shunt-regulated power supply.

Right, but that's not a true capacitive voltage divider.

The circuit is essentially a high-pass circuit and very
much has a rising response.

Those half-breed RC voltage dividers do need to be engineered carefully.