Yousuf said:I stand by my assertion, I've had different experiences than you. You
need to get some experience and follow your own advice.
You sound like you work for a UPS company, otherwise why are you so
invested in it? Just accept that people have different experiences than
you, and move on.
Rod said:David Brown wrote
Pity he was clearly talking about TRUE sine wave output, which only a
small subset of UPSs produce. And it aint even the continuous/online
UPSs that mostly do produce TRUE sine wave output.
Thats an entirely separate matter to TRUE sine wave output.
In theory that is correct. In practice there isnt a lot in it with
the brand name domestic UPSs now.
Thats not very much.
Thats overstating it, particularly with the stuff out of china.
Wrong.
Utterly mangled all over again.
And if you do care about that, you can also get replacement power
supplys that avoid the double conversion and still have the UPS
functionality.
Rod Speed wrote
I don't know exactly what you mean by "TRUE sine wave"
- all UPS's generate a sine wave of sorts when they are active
(i.e., all the time for continuous/online UPS's, or during power fail for standby devices). The quality of the sine
wave varies from fairly poor (lots of harmonics) to pretty good (few harmonics), but is /never/ pure.
If you are restricting discussion only to those UPS's that produce good quality sine waves,
then I'll have to take your word for how standby and online UPS prices compare. Baring the worst of the cheapo
devices, the sine quality of any UPS is going to be good enough for computer hardware, and is typically better than
you get straight from the mains. Thus it's not a restriction that I've considered.
True - though again, there is no such thing as "TRUE sine wave output", merely more or less harmonics.
OK. It looks to me that the difference has been getting smaller in recent years - perhaps we are merely arguing about
what sort of percentage is a "big" difference.
Nope.
I also have been looking mainly at APC, rather than a spread of suppliers - I've used them, I have found them
reliable, and they work well with Linux, so I haven't bothered looking at many alternative manufacturers.
In a recent purchase, the online device I bought was actually twice the cost of a standby device with similar ratings.
But that was because I needed it to work with a particularly hostile mains supply, thus it was a special case.
To be honest, however, the prices I saw when I checked APC's website surprised me slightly - I had expected a bigger
difference. But one should never let hard facts get in the way of a good argument.
Well, that's based on looking at APC's website.
There is no doubt that the cheapest APC standby device, which is perfectly good for a single system, is less than half
the price of their cheapest online
device. For their small devices, there is a huge difference in prices.
But as I say I haven't looked at other manufacturers - in particular,
I haven't looked at the low-end and unbranded devices.
I simply took APC as a familiar professional-level UPS supplier, and I expect other professional-level suppliers to be
roughly in line with them.
If what you are saying is true of the low-end devices, then that's
interesting news. I'm not sure I'd normally pick a no-name UPS
- when looking for reliability during a power failure, the supplier's reputation is a factor.
But there are certainly situations when a
cheap UPS is much better than no UPS.
Yep.
it's quite simple - AC to DC conversion has some loses, DC to AC conversion has some loses.
Simple passive filtering and surge protection, as used by standby devices when they are offline, has virtually no
loss.
I'm not too concerned about this myself, but other people certainly are, especially in larger setups.
If you are talking about DC supply buses to servers,
rather than having an AC supply to each, then I think it's a very good idea. It is quite simply idiotic to take a
high voltage AC supply, convert it to low voltage DC for a battery, turn it back to high voltage AC to deliver to a
server's power supply, which then turns it back to a low voltage DC.
Converting AC to 24V to 48V DC for battery storage, and passing that straight to a server's power supply
would be significantly more efficient in energy use,
and much smaller and cheaper in hardware.
Rod said:David Brown wrote
Should be obvious to even someone as stupid as you.
Wrong, as always. Plenty generate a square wave instead.
That last is just plain wrong.
I was JUST commenting on HIS claim about TRUE sine wave output,
****wit.
Completely and utterly irrelevant to the comment I made about his
stupid pig ignorant claim about TRUE sine wave output.
Wrong, as always. True sinewave is NO harmonics.
Nope, its just as true of desktop PCs.
It isnt idiotic, its just not as efficient. Many dont give a damn
about the efficiency with a device that isnt taking that much power.
Just as true of a desktop's power supply.
Not very significantly, actually.
Nope, its actually more expensive, essentially because that approach
doesnt sell in the same volume that traditional UPSs do.
David said:Rod Speed wrote:
Ed said:David, alot of us have Rod filtered out.
Rod Speed wrote
You might know about /buying/ and /using/ UPS's, but you don't know much about sine waves, AC/DC conversion,
harmonics, and related technicalities.
A square wave (as produced by very low-end UPS's) is just a sine wave with large harmonics.
And at the high end, good UPS's use PWM switching to produce something closer to a sine wave - even after filtering,
it is still not a "TRUE" sine wave.
I'll accept that the first part might be wrong - a square wave is a very poor sine wave, rather than just "fairly
poor".
As I have said, I haven't been looking at such low end devices.
However, if you think that UPS's generate *true* sine waves with no harmonics,
I'd love to see the circuit diagrams. I'd also like to know which brands go to great efforts to get closest to a sine
wave -
so that I can avoid them, as it would be a total waste of money.
So I can't talk about UPS's that don't produce mythical "TRUE sine
waves" because a previous poster talked about "TRUE sine wave" UPS's, but /you/ can talk about any UPS's you like?
I'm sure that makes sense to you, somehow.
Correct - a "true sine wave" has no harmonics. No UPS could possibly produce one.
There is no point in an UPS even trying
- it makes sense to limit the first few harmonics as much as practically possible, but you get very little gain from
going further than that.
Surely you are aware that a "true" sinewave exists only as a
mathematical concept - anything in real life is only going to be an
approximation?
<snip the incoherent rodbot responses>
I've only seen discussions of DC supply buses in the context of server racks, where you have lots of machines
together.
Since desktop PC's are typically spread out, you can't conveniently have a single AC to DC supply for multiple
machines.
True enough for machines with low power requirements. But the discussion here has moved on to multiple machines
- for server racks, the electricity price is often a very big part of the cost.
It is indeed true of a desktop's power supply - but unless a
significant percentage of users start using UPSs with their desktops,
the economics won't allow anything but AC supplies on desktops.
For people with big installations, even small percentages are significant.
But a rough rule of thumb would be 3-5% energy loss for each high voltage AC to low voltage DC conversion, assuming
top of the range converters. By avoiding the extra conversion to AC after the UPS and before the server supplies,
you'd save up to 10%.
Economics of scale are certainly relevant. But server rack UPS and supply systems are not huge volumes anyway,
and the energy savings would be appealing.
And the hardware itself would be smaller and a
lot cheaper once volumes are of similar magnitudes.
Rod said:David Brown wrote
Guess which pathetic little prat has just got egg all over its silly
little face, yet again ?
I was DESIGNING that stuff before you were even born thanks child.
Thanks for that completely superfluous proof that you have never ever
had a ****ing clue about anything at all, ever.
They are generated completely differently, fool.
Never ever said it was, ****wit.
Its nothing like a sine wave, fool.
You have always been, and always will be, completely and utterly
irrelevant.
What you might or might not have been looking at in spades.
Never ever said anything even remotely resembling anything like that.
It is perfectly possible to generate pure sine waves.
No one bothers with a UPS because there isnt any point in doing that.
Didnt say that anyone does, JUST that your stupid pig ignorant claim
that its NEVER possible is just plain pig ignorant and wrong.
Wrong. Its done for high power oscillators, ****wit.
Separate matter entirely.
Never ever could bullshit its way out of a wet paper bag.
Your problem, as always.
No one said anything about supplying multiple machines.
No it hasnt.
Like hell it is.
A significant number do use UPSs on desktops.
Wrong, as always.
Utterly mangled all over again. And thats not very significant
anyway.
Rod Speed wrote
I know I shouldn't bother responding here,
but it's hard to resist...
I'll try not to do it again.
Let me guess - you?
Really?
You were designing UPS's and inverters before I was born?
Perhaps you were making UPS's for IBM System/360 mainframes - there were not that many computers around before I was
born.
So forgive me if I find that claim just a /touch/ unbelievable.
As I say, you might know something about buying and using UPS's, but you clearly do not have any idea of the
electronics used in an inverter, or of the mathematics underlying them.
/I/ know how they are generated,
and how similar and different the generation is - /you/ do not.
The electronics is in principle the same
- it's just you need faster (therefore somewhat more expensive)
switching devices when you want to make something with less harmonics.
It also requires more effort in the controller and software (and therefore more expense).
In addition, different UPSs will have more or less passive filtering after the inverter - again, the principle is the
same, but some will spend more on the components than others.
And as I said, a square wave is just a sine wave with large harmonics
(I didn't mention how they are generated).
Ever heard of Fourier?
For someone who has been designing UPS's for nearly forty years, your mathematical knowledge is somewhat lacking.
So you now agree that there is no such thing as a "TRUE sine wave" output from an UPS?
It's a pity that you then contradict yourself /again/ later on.
Here's a couple of links for the mathematically impaired:
http://mathworld.wolfram.com/FourierSeriesSquareWave.html
A square wave is a sine wave with a lot of harmonics.
The relevance and effect of these harmonics will depend on what you do with the output,
but you can't argue with the basic mathematical facts.
Well, /you/ apparently /can/ argue with them, but you look a bit silly by doing so.
And for a final clue, let's try to think of an example of a real
application where a square wave is used to replace a sine wave.
I know, how about connecting a square wave output from an UPS to the power supply of a computer, designed to work with
a sine wave mains voltage. My goodness - it works! It's almost as though the square wave does the job of an
approximate sine wave!
So you now agree that "TRUE sine wave" UPS's, as you have been calling them,
don't generate true sine waves? In fact, you now agree that
/all/ UPS's generate approximate sine waves with harmonics?
Pray, tell me how to do so.
If you can produce a /pure/ sine wave, I've got a perpetual motion machine I'll sell you.
Remember, we are talking about *pure* sine waves,
not just something /close/ to a sine wave.
At least you've learned that much from my posts.
So you agree that these "TRUE sine wave" UPS's you've been talking about are mythical?
You even agree that close-to-sine UPS's don't exist because no one wants to pay for them (though it would be possible
to make them).
Yep.
you do not use a "true sine wave UPS" for a high power oscillator
- you don't necessarily use an UPS at all.
Assuming that by your mangled attempt at a sentence,
you meant to say that a "high power oscillator" is a "true sine wave" generated by an inverter like an UPS output,
then you are still wrong.
A "high power oscillator" will generate it's signal in different ways, depending on
the application. And in particular, it will /never/ generate a /pure/ sine wave.
It might have very low harmonics, depending on the needs of the application, but it will never be pure.
You don't understand the mathematics involved, and you don't understand the electronics.
That's okay - you don't need to know how these devices work to be able to use them.
And just because I /do/ know how to design UPS's and power supplies of different types and ratings,
doesn't mean I know more about buying or using them than other people. But you certainly look pretty foolish with all
your claims about impossible devices because you don't understand the principles.
Again, you've learned.
Well, you've learned /some/ things. Perhaps it's time to re-take the remedial mathematics classes.
Yes, some talked about supplying multiple machines - /I/ did.
Has no one explained to you the concept of having a discussion involving more than one person?
I forgot - you were /designing/ this stuff before I was born.
Yep.
Go back to sleep in your rocking chair, old man, and dream of the sixties when you knew something worth knowing. The
rest of us here in 2009 know that electricity costs are entirely relevant.
Significant as a percentage of desktop users?
Yep.
I'd be surprised if it is more than a couple of percent.
Feel free to provide a link proving me wrong.
Again, I'd recommend those mathematics remedial classes.
A small percentage of a very big number is still a big number, and therefore significant.
You are remembering I was talking about big installations?
Are you sure you're not a banker?
With claims like that, that 10% savings on your main running costs being "not significant",
you sound a lot like the half-wits that brought us the current world economic situation.
So you now agree that there is no such thing as a "TRUE sine wave"
output from an UPS? It's a pity that you then contradict yourself
/again/ later on.
David said:Well, I know of one design that I'd call same; but not sure you will.
The best ferro-resonant UPS's are damn close. Of course, such are neither
common or inexpensive.
[But then the line itself is never purely sinusoidal, either; it come
with flaws such as spikes and dropouts...]
The real question is: does the load care if it's not? If all loads are
switchers, usually not at all. Linear wall-warts may. Incandescent lamps
won't have a clue.
David Lesher wrote
I've no argument that you can generate very close to sine waves
- for most practical purposes, devices like these are effectively sinusoidal with no harmonics that you normally need
to consider.
Every application has its requirements for how good a sine wave it needs,
and you can get as close as you like (until you are limited by fundamental things like thermal noise).
I've just been arguing about rodbot's descriptions of UPS outputs as "true sine wave",
and his claims that things like rotary converters and the mains supply produce /pure/ sine waves with absolutely no
harmonics.
[But then the line itself is never purely sinusoidal, either; it come with flaws such as spikes and dropouts...]
The real question is: does the load care if it's not? If all loads are switchers, usually not at all. Linear
wall-warts may. Incandescent lamps won't have a clue.
Incandescent lamps /will/ care - they will prefer a square wave,
because there is less variation in the absolute current, and therefore less variation in heating.
This means less thermal and physical stress,
and a longer life for the same power output.
But I agree that the question is if the load cares or not. For many purposes, a square wave should be better
(though DC would be best),
but most devices are specified, optimised and tested with AC (at least roughly sinusoidal) inputs.
Rod said:David Brown wrote
And that is clearly what the OP was talking about when he used the
term TRUE sine wave.
What matters is that they are at least as close to a sine wave as the
mains they replace.
What matters with a UPS is that the sine wave is at least as good
harmonics wise as the mains it replaces.
You arent necessarily even limited by that.
Wrong, as always.
Mindlessly silly. They dont give a flying red **** about the current
being less than the peak current. In fact that increases the life of
the filament, fool.
Only in your pathetic little pig ignorant fantasyland.
Only in your pathetic little pig ignorant fantasyland.
They in fact prefer a less than sudden current rise, if only because
you dont get as much magnetic field effect with the coiled filaments
etc and less thermal shock with the initial turn on when the filament
cold resistance is lowest.
**** all in fact.
Try sticking that into a switcher and see how well it works.
Rod Speed wrote
It seems unlikely that you'll ever understand what "true" means in this context.
I know perfectly well what sort of quality sine waves real-world UPS's can generate, but when you insist on using a
precise technical expression like "true sine wave",
even emphasising the "true" with capitals,
you need to be corrected.
In the case of specialised UPS's as mentioned by the previous poster (you snippet the quotation),
the waves should be a lot /better/ than typical mains supplies.
Mains varies a lot in quality - the voltage can vary quite substantially from average ratings, you get spikes and
droops, phase distortions, harmonics, and short-term variations from the ideal 50 (or 60) Hz.
Yep.
what matters is that it is good enough for the application.
Those pesky fundamental physical limitations causing you trouble again?
Nope.
Yes, you are limited be thermal noise.
Nope.
You can reduce the thermal noise greatly by cooling, of course, but you can't eliminate it entirely.
And even if you want to run your system in liquid helium, you've still got quantum effects.
There are three issues with changes in current.
Nope.
One is the initial startup heating and thermal shock from a cold filament. That's the biggest shock, and the most
likely time to blow the bulb.
The sine wave reduces that slightly on average compared to a square wave
- but for each time the light switch is activated, the actual initial inrush current will depend on where you are in
the 50 Hz cycle.
And of course, switch bounce in your average light switch will ensure that
each time you turn the light on, it will be hit by several full voltage blasts.
Then you've got the effect of the I^2R heating. With AC, this will vary between zero and full effect 100 times per
second, leading to changes in the temperature
and thus thermal stresses at this rate - the thermal mass of the filament is not enough to smooth out these changes.
With a square wave, the absolute current is the same except for brief pause when the polarity changes. These pauses
are much shorter than for a sinusoidal current, and the current between the pauses is far more consistent. Thus there
is much less thermal stress.
You also mentioned changes in the magnetic field as the current changes. Yes, this will happen - but the inductance of
the filament coil is very low,
and the rate of current change is not /that/ high
even in a square wave output UPS (we are talking real-world supplies here, which have at least some passive
filtering).
The magnetic field changes have two effects in the filament - one is to oppose the current changes (increasing the
time when the square wave is not at its consistent full current), and the other is physical forces on the filament
itself from its magnetic field. Both of these will be very minor effects.
That depends entirely on what you are using.
Many power supplies have a very simple bridge rectifier on the input - they'll be as happy with DC as AC.
Others depend on the AC - an obvious example is if you have a transformer.
David said:<snip>
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