PSUs, UPSs, PFCs, and Sine Waves

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Cybernetic

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Jan 7, 2012
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I was about to buy a $60 UPS from Amazon when I came across a review from a user talking about how his computer would not boot up because the UPS did not provide the require sine wave (provided a stepped sine wave).

I looked around Google and various forums regarding the issue, but some of the material is dated. From what I understand, a common UPS will create a stepped sine wave (or a square wave) from the DC output for the PSU. Some PSUs (possibly including my Antec 750W in the signature) will respond by shutting off power. This defeats the purpose of me buying a UPS in the first place.

So I looked around for "pure" sine wave UPS and the cheapest is $120+ with better quality ones reaching into the $200+ range which is absolutely ridiculous. At this point, I have a couple options:


  • ■ No UPS (this would be a bad choice from every reply I've seen on the subject)
    ■ Buy stepped sine wave UPS and hope my PSU is compatible (already bad feeling about this option)
    ■ Sine wave UPS (very expensive, budget restrictions)
    ■ New PSU that would accept stepped sine waves (SeaSonic was mentioned, any other brands?)
Out of all these, I think the last one of buying a new PSU would be the best option (maybe not? let me know). If it is, which brands are known to be good? I'm looking for 750W 80+ Gold.

Note on PFC: The supposed cause (since I'm no expert) of the incompatibility is because active PFC will detect the improper wave and respond by shutting off the PSU.

I would like to prevent damage to a new system from brownout or surges, but power outages are very uncommon in my area. If a UPS is recommended, I only need a few minutes to save my files and turn off the computer.

Thanks
 
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Videographer

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If you get a UPS get a pure sine wave one that has a built in power regulator. There are also models that pass the mains straight through and kick in as soon as the voltage drops but I don't know if these models are more expensive
 
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C

Cybernetic

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Yes, I saw those, but every UPS with a pure sine wave is very expensive. I was hoping TH could provide some alternatives or recommendations.

For anyone curious about the built in regulator, I think they are called "line interactive" UPSs.
 
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Pinhedd

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Stepped sine waves are fine (a stepped sine wave is not a square wave), square waves are probably not. The reason this occurs is because UPS use digital signal processors to drive digital to analogue converters which drive high power amplifiers which in turn invert the UPS's internal DC storage into AC output which in turn drives a step up transformer which is then connected to the UPS AC output. The power on a wall outlet on the other hand is derived from a spinning electric generator so it has a continuous arc. Even high quality UPS will use the same method of power inversion (although some may perform it in a different order), it's the most efficient way to do so short of mechanically coupling a DC motor to an AC generator. However, a high quality UPS may use more capable components which generate a more ideal output waveform.

The most likely culprit is the $60 UPS, it may not have been up to the task. A $60 UPS is to a PC as a $60 driver side airbag is to an automobile, there's a point in which budget becomes useless or even dangerous. $200 is not ridiculous for a UPS it's actually quite par the course. Heck I have a 3000 VA rackmount UPS that retailed for $2,000 (hooray for surplus equipment!)
 
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ko888

ko888

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Feb 18, 2009
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The CyberPower CP1350PFCLCD will work absolutely fine.

Surge protection is already built into the UPS.

Incompatibility with simulated sinewave UPS' is a result of the incompatibility between the PSU's Active PFC circuit and the UPS' output waveform while operating on battery power. If the output waveform has a high harmonic distortion some PSU's APFC circuit will be unable to deal with it and will shut itself down. The higher the power draw from the UPS the more distorted the UPS' output waveform becomes. Some Seasonic PSU models are incompatible with a simulated sinewave UPS. Brand is not what determines compatibility.
 
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C

Cybernetic

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Neither of the UPSs are returnable. If my PSU is not compatible with the APC, I will end up with a very large and expensive paperweight (as I have no other use for it) with a $200 dent in my wallet.

Would I be better off getting something that explicitly states that it is PFC compatible or get a high quality stepped UPS from APC (one of the reviewers also had issues with his UPS not being "pure" sine)?
 
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