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UPS with the best (purest) sine wave output

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Last response: in Components
August 7, 2008 12:20:52 PM

I need a UPS with pure sine wave output. When the specification says "pure sine wave" or "sine wave" (I've noticed e.g. APC uses word "pure" nowhere), does it mean the output is pure sine wave comparable with the utility power?

Or is the "pure sine wave" only a better approximation of a stepped sine wave? In that case what is the cheapest UPS with the best sine wave available?


More about : ups purest sine wave output

August 7, 2008 1:01:19 PM

What are you trying to do? Is this for Hi-fi A/V? Medical equipment?

I presume you already know that utility power is anything but a pure sine wave...
August 7, 2008 4:26:18 PM

I work with ups's daily

Here you can see that there 'Pure' sine wave ups's aren't called it pure \/ - I love these, banks use them all around the world

Here you can clearly see that this isn't pure, it's Stepped approximation to a sinewave \/

Matter of fact, they don't even state 'pure' on their $10-20k ups's. If you have a problem with their style of naming, you can email them a complaint. Pure isn't a word manufactures have to use, some use it, some don't. In reality, there's no such thing as a trully pure sine wave ups. Find your nearest Electrical Engineering company or school and they'll be glad to explain this to you.

You don't necessarily need the best sine wave for general home pc's.
Get this one and be done with it.

'Pure' sine wave, almost 40 amps (this means "at-least" 1.5 hours of power for one pc), 950+ watts and easy maintenance.

Email APC for any further questions you have, your the costumer and it's your money.
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August 9, 2008 11:45:07 AM

TeraMedia said:
What are you trying to do? Is this for Hi-fi A/V? Medical equipment?

I need to back-up every kind of equipment. Wattage is not an issue but what I need is a prolonged running time on battery. And I have bad experience with stepped sine wave UPS. The PSU of my computer started buzzing every time it was on battery in such a way I was feeling it's going to explode. It was like very high voltage wires.

As I found the PSU manufacturer doesnt recommend using stepped sine wave but I had the same problem with monitor and other equipments (albeit they weren't buzzing that loud). So it's more UPS than PSU issue.

TeraMedia said:
I presume you already know that utility power is anything but a pure sine wave...


No, I don't know that. As far as I remember physics the power is generated by a magnetic rotor inside a magnetic stator (sorry for bad translation) - what should generate pure sine wave.
August 9, 2008 11:54:46 AM

In reality, there's no such thing as a trully pure sine wave ups.

what? can you elaborate or post a link to some articles that address this issue? Does it mean that every UPS I eventually buy will stress the connected equipments when running on battery?

You don't necessarily need the best sine wave for general home pc's.

I do. As I just wrote one post above I need prolonged time running on battery without overly stressing the connected equipments...

Email APC for any further questions you have, your the costumer and it's your money.

I did (actually the same time as I was setting up this thread). But I need some independent opinions because the sellers will never tell you everything (even if they are ultra-fair to their customers they still have an insider view which causes distorted perception).

That's why I need some independent opinions and I thank to everyone who gives me some!
August 15, 2008 7:41:11 PM

I took a look at the output of my APC sine-wave UPS and it is noticeably cleaner than the mains itself; so purity may no longer be an issue (The various local loads distort the mains).
a b ) Power supply
October 7, 2009 12:32:00 PM

I'll try to make a quick comment here. Most UPS's use cheap and easy methods to provide 120VAC outputs. They switch abruptly for each cycle using components like SCR's or High Current Darlingtons - but they have minimal filtering to keep the expense and complexity down. The output is more of a square wave than a smooth sine wave. If you're familiar with some of the engineering, it's 60 Hz +/- a lot of other frequencies that you don't need.

When used with older equipment with transformer power supplies - including computers (they have pretty decent filtering) - no harm is done. The non-60 Hz frequencies are either rectified into DC with a little more noise or filtered.

But these UPS's pose a danger to newer solid state equipment. Solid State power supplies use SCR's to produce DC from AC. They are designed for sine wave power, using a specific voltage level to trigger a particular side of the DC conversion. (on the positive and negative swings). When the SCR is on, it is conducting full current. When they are using norman sine waves, it is turned on for only a small portion of each cycle.

But when the power is a square wave, the voltage threshold is reached almost immediately per cycle. This causes the SCR to be turned on for about 90% of the time. The components will overheat and burn out if not protected. This means a dead power supply in that brand new $4,000 LED TV. If I pull the plug on mine, I can hear the TV power supply switching violently (it makes a rather audible 'eeeeeeeeeeeeeeeeeee' sound. That's not good for more than a few minutes - the SCR's will overheat and die.

Be VERY careful when using cheap UPS's on new televisions. They work well to prevent damaging undervoltage or long time variant spikes due to power line disconnects (or lightning triggered interrrupts), but they are NOT to be used long term. If you have the money, buy a "pure sine wave" product. It will be more expensive and bigger due to the filtering and regulation components, and a bit less efficient, but it will provide power to your equipment in a form it was designed for.
a b ) Power supply
October 7, 2009 4:30:14 PM

Desertengeneer. Minor Disagreement, As a shi%$^ input to a xformer can cause it to "Sing", overheat, or burn a winding open.

Nonsineasodiol waveforms poise a big problem for transform input. Example (Extreme case) if you applied a 120 VAC sinewave to a 10 to 1 stepdown xformer, you get a nice 12 VAC output. If you were to apply a 120 VAC squarewave you would get a positive spike with a short decay to zero then a neg spike decaying to zero (Delay will look like a RC curve. The output of the transformer is zero during the plateaus (Eout is dependent on rate of change – there is no rate of change for a square wave except durning the leading and lagging edges. This leads to rapid distruction of the Xformer as Current is only limited by the DC resistance of the winding, Very high, as opposed to the higher X sub L reactance. UPS typically have a very poor output waveform with the cheaper ones having a sharp leading edge..

As you pointed out the output is typically a pulse modulation of sinewave controlling the on time. It is the transition from on to off that creates the problem (as you pointed out). Also as you pointed out this sharp transition (Composed of very High freq) is what causes the eeeeeeeeee sound.

I would ask the manf to provide a waveform of the output under MAX recommended loads.

Cost, size, and Weight (emphasis on COST) are the determining factors. A true Sinewave cannot be produced by a switcher PS unless that output is rectified and used as the DC to a RCL, or Xstal controlled oscillator and applied transistor amplifier. For High current this is rather large and costly (also low effiency).

Might be cheaper to buy a generator.
December 31, 2009 7:00:39 PM

You guys are way over my head but I am in need of a pure sine wave UPS. Apparantly some of the HP/Compaq desktop line is now requiring pure sine wave and it only took me 3 different APC UPS to figure this out.

I replaced the battery in an old Back-UPS 800 RS, that didn't work. I ordered a Back UPS 900 RS because I thought the old 800 was just bad, that didn't work. So I ordered a Back-UPS 1200 RS (same thing we use on our engineering work stations), to my dismay, that also did not work. I called HP and after a good bit or research the call center guy found this article.

Do you guys have any pure sine wave model APC that would be ideal for keeping a desktop PC up though very brief power interuptions?
January 21, 2010 4:50:51 PM

I'm having this problem with several HP dc7900 SFF computers. They are currently using CyberPower CP600LCD (340w 600va) battery backups but apparently these don't have the "true sine wave" because the power went out today and they all shut down immediately. Does anyone know if there a UPS around the $100 price range that has this feature? I have been looking through APC's website, but I have not found anything yet.
April 8, 2010 8:58:22 AM

buy a netcaa ups its pure sine wave and working 100%. i have 1200VA and its very good with lcd screen for load and voltage, battery status display etc.
April 14, 2010 6:53:36 AM

Let me start by saying first, I am a "purist" and enthusiast and snob who is a little paranoid about things like knock-off jeans and "unclean" power sources.

So you could say that I too like the idea of "pure" power. But this is crazy talk. Unless you are trying to protect sensitive hardware (medical & audio recording / production), you have somehow snagged yourself on the necessity to have a Pure Sine Wave UPS.

No system manufacturer is going to require or recommend that you feed their third-world-assembled, mass-market circuitry with enterprise-grade power. A Pure Sine-Wave UPS would cost you at least 25% of the cost of even the most high-end desktop system.

If you're using enterprise grade components in your desktop system, then maybe you could rationalize protecting your investment with a $500-$600 UPS. But even mission-critical equipment like banking and data servers don't need Pure Sine Wave; they just demand highly stable and consistent power.

Yes, pure-sine wave power inverters and UPSes are indeed 'better' by virtue of the task they perform, but most likely you talked to someone who was also an enthusiast purist nut job who himself placed value on the simple 'better' aspect without context, and it fueled your own paranoia.

Really, a line-interactive UPS with AVR will do. Just get one with sufficient output to cover all the devices you want to operate "uninterrupted." And if you still disagree, I'd love to see a link to those specifications.
a c 194 ) Power supply
April 14, 2010 7:38:45 PM

My Antec SG-650 will not run on the approximation of a unit like an APC BE750; it shuts off immediately. I got a SUA-750 though, and that works perfectly, and wasn't too expensive.
a b ) Power supply
April 14, 2010 10:04:25 PM

needathing said:
what? can you elaborate or post a link to some articles that address this issue? Does it mean that every UPS I eventually buy will stress the connected equipments when running on battery?

You are getting no useful answers for an obvious reason. Nobody is posting numbers. For example, if that APC outputs 'pure' sine waves, then it provides numbers that define that 'purity'. APC is selling to people easily deceived with subjective reasoning.

Using the same subjective reasoning, the stepped sine wave output is also pure sine waves. You only need remember Fourier Series in high school math. Stepped waves are nothing more than a sum of 'pure' sine waves.

All electronics is so robust that a stepped wave causes no hardware damage. That same stepped wave can be harmful to electric motors and power strip protectors - devices that are less robust. But any UPS output is perfectly ideal power to any and every properly designed electronics.

Nonsense is that 'fear' due to noise. Sometimes coils are not completely sealed (internally) by a varnish like material. So a wire may vibrate at certain frequencies. Harmful to you fears. Irrelevant to electronics.

No AC is pure sine waves. And no reason to discuss what is obvious once you learn about the so many electrical anomalies such as those created by all electronics - that 'sip' power from the top of sine waves. All AC mains have harmonics, power factors, and other anomalies. To get a UPS that only might be cleaner that AC mains, start at $500.

How long do you need power? The plug-in UPS is only for temporary power so that data can be saved. If you need better, then you need a serious power source such as a Honda generator or a serious building wide UPS - typically many $thousands.

Why do you know that 'dirty' AC power is irrelevant to electronics? This is what a minimally sufficient power supply does to the cleanest and dirtiest power. First, some serious filters. Then converts AC to high voltage DC - exceeding 300 volts. Then filters again. The converts to high voltage radio frequencies with sharp rising spikes. Then more filtering and galvanic isolation. Then converts high voltage RF to high current RF. Then converts that RF back to DC. Then more filtering. What changes with 'pure' sine wave or the 'dirtiest' UPS? Nothing. The output is completely unchanged no matter which UPS is used. And now you know why. Worry more about 'damage' from the high voltage radio waves generated inside every power supply. But that means you would conclude based in how things really work. An overwhelming majority who recommend do not every learn the essential details AND never demand those always required numbers. Not in popular fears exaggerated by noise.

If a UPS has 'pure' anything, then only numbers say so. Otherwise it is only 'pure' bullshit from a communication major or business school graduates. Subjective claims from those aught to know only from speculation - to spin. How to know who is lying? Recommendations without numbers. People taught more about deceiving that designing. Their half truths and lies have you worrying emotionally about myths rather that thinking logically. If honest, then every post included numbers such as THD. No numbers so that you do not learn how crappy all power really is. And then learn that crappy power was always made irrelevant by electronic hardware designs more than 40 years ago.

If AC mains power gets crappier, then what is firstmost at risk? Refrigerator, furnace, washing machine, etc. Dirty AC mains must remain clean enough so that less resilient appliances are at less risk.
April 15, 2010 2:58:20 AM

Onus said:
My Antec SG-650 will not run on the approximation of a unit like an APC BE750; it shuts off immediately. I got a SUA-750 though, and that works perfectly, and wasn't too expensive.

Ah dude, then you either got a bum SG-650, a bum APC BE750, or have bought a sham product. When you called Antec to tell them your PSU wouldn't power up reliably, they fooled you into not returning the unit. If you never called, your fault. Congratulations, you now have a $300 UPS to go with your $170 PSU.

FYI, if you read Antec's site, nowhere in the product manual or specifications does it indicate the requirement for pure sine-wave power sources. In fact, if you read the section about its PFC feature, you'll find direct references to the SG 650 technology meant to counteract issues with direct-to-wall power problems.
April 15, 2010 3:06:33 AM

This thread has been disturbed in its grave too many times.