UPS advice - stepped sine wave or pure?

tgfyhre · 23 Jun 2015

My APC battery backup UPS needs a new battery, and I'm considering getting a new unit, as mine is approaching 5 years old. I've been reading that standard UPS devices put out a stepped sine wave that can cause issues and possible damage or reduced lifespan with newer Active PFC Power Supplies and LCD monitors. Cyberpower make some that output a "pure sine wave" that is supposed to be better for PFC hardware. Is this really an issue I should be concerned with?

There are 2 UPS units from Cyberpower I'm looking at - 1 has 12 outlets which gives me 2 more than I currently have, which I could definitely use. But it only puts out a standard stepped sine wave. Then there's a similar one with only 10 outlets that outputs a "pure sine wave". Is it worth getting the pure version and losing 2 outlets, or is it not as important as some are saying? I want to do what's best for my equipment of course, especially because I tend to get random power outages for anywhere from a few seconds to a few minutes fairly often - enough to warrant owning one of these units.

logicearth · 23 Jun 2015

You really don't need to pay that kind of money. A "pure" sine wave is no better or worse then a stepped sine wave. Not to a properly designed power supply. A properly made power supply filters the incoming power and filters the out going power. In either case the power from an APC is cleaner then what is coming from the Mains directly.

So here is my advice. Forget the sine wave nonsense and get what you can afford that gives you the backup time you need.

tgfyhre · 23 Jun 2015

Thank you. I didn't know what to think after reading some of the information out there about the PFC power supplies not liking the stepped UPS units. Your advice goes against some of what I've read that state there is indeed a difference that can affect PFC power supplies.

I have read several comments and sites that talk about the buzzing from a power supply when a stepped UPS is used. I do notice that when my older APC UPS kicks in, instantly I get a loud click followed by a buzzing sound. Comments seem to say that the buzzing sound is the power supply and is a result of a PFC power supply not liking the stepped power from the UPS.

I'd love to avoid the extra cost and gain extra outlets on top of the savings - I just want to make sure that I don't regret it later. Why do some sites state that it's so important to go with a pure sine wave?

Even APC's site seems to suggest that their units aren't intended for active PFC power supplies. And there are reviews that state their PFC power supplies don't work at all well with stepped UPS units. Very confusing.

This was found on another forum, where the poster spoke with APC regarding this issue:

"I just spoke with both Silverstone and APC. Silverstone is going to get back to me on this question, but APC was pretty clear -- they strongly felt that PFC power supplies should use true sine wave UPSs. They told me that the reason for this was because PFC power supplies require a much faster changeover time when the battery kicks in, and that due to the design of stepped sine wave UPSs, they were not always fast enough to satisfy the power supply. This could lead to the PSU shutting down when the battery tried to kick in. The guy I spoke with said that the stepped sine wave wouldn't "damage" the PSU, but that it simply might not work, and that if it DID work, it might not "always" work. Apparently it depends on the specific power supply."

Lady Fitzgerald · 23 Jun 2015

logicearth said:

You really don't need to pay that kind of money. A "pure" sine wave is no better or worse then a stepped sine wave. Not to a properly designed power supply. A properly made power supply filters the incoming power and filters the out going power. In either case the power from an APC is cleaner then what is coming from the Mains directly.

So here is my advice. Forget the sine wave nonsense and get what you can afford that gives you the backup time you need.

Bad advice. The older PSUs could operate OK on a stepped sine wave but many of the newer PSUs, and some peripherals, need pure sine wave power to function properly. Many PSU vendors, such as Corsair, recommend using only pure sine wave to power their PSUs. Pure sine wave doesn't cost all that much more and future proofs you for later components that may be more particular.

As far as number of outlets goes, if the UPS can handle the load, you can always use a power strip or multi-outlet extension cord plugged into the UPS. I did that with my UPS; I have my three monitors plugged into a three outlet tap that connects to one of the UPS outlets via a short extension cord. My UPS can easily handle the load even though I ran out of outlets on the UPS (part of that was due to a wall wart PSU for my HDMI splitter). Right now, I'm using only 270 watts and the UPS is rated for 1500 watts (I have 99 minutes runtime available on batteries right now and I've never gone over 375 watts consumption so far).

tgfyhre · 23 Jun 2015

And this is why I'm confused. I hear two different stories.
Here's what Silverstone had to say in regards to this issue, as posted by the same person I quoted above:

"Okay -- here is a follow-up response from the Silverstone engineer in Taiwan (with good news for those of us in the US.)

"It is fine if you living in US and used 120V input in your OP700, even by a not pure sineware UPS."

This is of course good news for those of us in the US. This is direct confirmation from Silverstone that if you're in a country that uses a 120V standard, you CAN use non sine wave UPSs without damaging their power supplies."

Here's a link to the thread:

Active PFC Power Supply and NON true sine wave UPS. - Page 5 - jonnyGURU Forums

Of course that's an older thread, so I don't know how much has changed.

Lady Fitzgerald · 23 Jun 2015

That article is seven years old. More PSUs are PFC now and more of them are intolerant of stepped sine wave. Why spend the money on a stepped sine wave UPS only to discover your PSU won't work with it?

tgfyhre · 23 Jun 2015

Well, I agree - that's why I created this thread. I want to make sure I get the right UPS to handle newer power supplies, monitors, etc.

All I know is my current PSU buzzes very loudly when my APC UPS kicks in, and that UPS is a stepped sine wave.

So why does the industry make and sell stepped UPSs that are clearly marketed for household PC use when they are a poor idea to use with modern power supplies? This is baffling to me. I never would have even known about any of this and just bought another stepped sine wave model if I hadn't just stumbled onto a comment about this issue.

That thread is old but it's 15 pages and more recent posts are from last year.

tgfyhre · 23 Jun 2015

Here are a couple video reviews on youtube that talk specifically about this issue and the Cyberpower UPSs:

https://www.youtube.com/watch?v=DoIW0Jh-K0A
:40 he starts talking about sine wavs with this UPS

https://www.youtube.com/watch?v=ViGZ...54-9Ww&index=4
3:40 he starts discussing the same issue

Either they're both wrong, or it's pretty important to get one with with a pure sine wave.

Lady Fitzgerald · 23 Jun 2015

The fact that your PSU buzzes when running off stepped sine wave is plenty reason to go with a pure sine wave UPS.

As to why manufacturers still sell stepped sine wave UPSes? There are some to many PSUs that can run on them. Also, PSUs aren't the only thing people use with a UPS. Many of other things people put on a UPS can run fine on Stepped sine wave.

I wouldn't take too much stock in what Johnny Guru has to say. He is supposed to be a PSU expert but I have seen him give some questionable advice fairly recently, particularly on UPSes.

Lady Fitzgerald · 23 Jun 2015

tgfyhre said:

Here are a couple video reviews on youtube that talk specifically about this issue and the Cyberpower UPSs:

https://www.youtube.com/watch?v=DoIW0Jh-K0A
:40 he starts talking about sine wavs with this UPS

https://www.youtube.com/watch?v=ViGZ...54-9Ww&index=4
3:40 he starts discussing the same issue

Either they're both wrong, or it's pretty important to get one with with a pure sine wave.

I just watched parts of both. Both were dead on with why PSUs should use pure sine wave power but, curiously enough, both gave a somewhat inaccurate description of what a stepped sine wave (also known as a modified sine wave) looks like. Both described a square wave. Stepped sine wave uses groups of square waves but varies the voltage of each square wave so each group approximates the curve of a sine wave. Btw, I've watched a lot of videos from Linus and this is only the second and third time I've seen him get some detail detail (he also missed defining the voltage of a sine wave in the video but also had some text appear that corrected it).

But I'm into nitpicking now. For the big picture, both gave excellent advice.