Observations on a UPS - follow up to a previous post

[James Sweet]

"James Sweet" wrote ...


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.

 

[Doc]

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.

 

[Doc]

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.

 

[James Sweet]

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.

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.

 

[Arfa Daily]

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.


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

 

[Arfa Daily]

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

 

[Doc]

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.

 

[Arno Wagner]

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

 

[Arny Krueger]

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.

 

[Arny Krueger]

"Arny Krueger" wrote ...

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.

 

[Arny Krueger]

In comp.sys.ibm.pc.hardware.misc Doc

Seems like it is discontinued - not on their current store list.

The price is all wrong.

(1) Made in China, sold in the US
(2) House brand
(3) Close out

Nobody can build a decent product
with these specs for that price.

Best Buy is actually the high priced spread, compared to some of their
competition.

You cannot even buy the
components needed in decent quality for that price.

But that is unit one up individual component pricing which has a lot of
overhead in it.

 

[Arny Krueger]

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.

Spend more money or wait 3 years! ;-)

 

[Scott Dorsey]

I read recently that the memory effect "myth" was created due to cheap
chargers overcharging the batteries unless they were first fully discharged.
A decent intelligent charger should prevent this, and batteries have in
theory improved as well.

No, there actually _was_ memory effect at one time, and the Gates Battery
Handbook used to have a discussion about the chemistry involved. The
problem was solved some time in the late 1970s, but the notion on the part
of the users remained. And plenty of users since have destroyed perfectly
good battery packs by deep-discharging them and wrecking the weaker cells in
the pack, in order to avert a failure mode that hadn't existed for years.
--scott

 

[Scott Dorsey]

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 ;-) )

In the US, the high voltage distribution is done with three phases, shifted
120' from one another. You can also in many places order low voltage lines
with three-phase power, but it's not common in residential areas.

In most residential areas, they will send one leg of that three phase 3KV out
to a distribution transformer near your house. The secondary of that
transformer has a center-tap tied to the neutral, and then two hot wires
that are 180' out of phase. So neutral to one leg is 120V, but leg to leg
is 240V.

But this does not help you if you want to run a 25-foot turret lathe in
your garage, which requires three phases with a 120' shift between them.
For that, you either have to move to an industrial neighborhood, or call
the power company to pull three-phase 3KV in and then drop it down to
a low voltage with your own set of transformers. They will charge for this.
--scott

 

[Arno Wagner]

In the US, the high voltage distribution is done with three phases, shifted
120' from one another. You can also in many places order low voltage lines
with three-phase power, but it's not common in residential areas.

In most residential areas, they will send one leg of that three
phase 3KV out to a distribution transformer near your house. The
secondary of that transformer has a center-tap tied to the neutral,
and then two hot wires that are 180' out of phase. So neutral to
one leg is 120V, but leg to leg is 240V.

That would be 210V leg-to leg, because of the phase shift.

But this does not help you if you want to run a 25-foot turret lathe
in your garage, which requires three phases with a 120' shift
between them. For that, you either have to move to an industrial
neighborhood, or call the power company to pull three-phase 3KV in
and then drop it down to a low voltage with your own set of
transformers. They will charge for this.

Hmm. The typical approch in Europe is 15kV to large transformers
and then 3 phase distribution to the houses. Above ground is for
is moslty for rural areas, you do not see above ground lines in
cities, at least not in Germany or Switzerland. So getting three
phase is trivial. Typically flats have 3-phase times 16A (at 240V)
for electric stoves. Getting 3x25A at 240V is just some in-house
wiring. If you want 3x40A, you may need to have your feed checked,
since it is typically rated at 3x63A or 3x100A for larger houses.

Arno

 

[Arno Wagner]

Spend more money or wait 3 years! ;-)

If you select your LCD carefully, you can get really good ones
for very reasonable prices. I have a Benq FP73G, which initially
anoyed me a bit with the vertical brightness dependency on viewing
angle. Now I do not notice it anymore. It is sharper than CRT by
at least one order of magintude. Of course you have to run at
native resolution. As with brighness, I found that I needed to
tweak gamma in some games. apart from that, no problems.

Arno

 

[Meindert Sprang]

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.

Then you should buy a decent flat panel. I went from an IIyama 22" CRT to an
IIyama 20" LCD and it is razorsharp compared to the CRT. And regarding
viewing angle: even watching from aside (175 deg.) it still looks like
watching a picture on a piece of paper.

Meindert

 

[Scott Dorsey]

That would be 210V leg-to leg, because of the phase shift.

No, it's 180' phase shift. The two legs are directly out of phase,
therefore they sum. It's not three-phase, it's what they call
single-phase (even though it's really two phases).
--scott

 

[Richard Crowley]

"James Sweet" wrote ...

...

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.

There are rumors that the manufacturer re-designed the
circuit to eliminate this flaw. It may not be a problem with
newer models(?)

The original problem was featured in a 2-page article in the
ham-radio magazine "QST".

 

[Richard Crowley]

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

You are correct. I mis-characterized it as a "capacitive divider"
when only the series element was capacitive.

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

Rumor is that the manufacturer re-designed the circuit to
eliminate the problem.