I moved to an area/building where there are quite some problems with the wall-power supply. Primaraly I would like to protect my computers, secondary I would like have some affordable UPS for some of them.

Common advice is a online-ups systems, but they are expensive in the initial purchase, and also they use a considerable amount of power

A 90% efficient 1000W UPS for example, fully loaded, will consume 100W of power continuously.

quote from page 11

during the time that the power is ok, because they are constantly doing a power conversion subjected to loss.

There are some quite affordable "Line-Interactive" UPS around (which dont have much additional power consumption) but most of those have modified sine output, which appear to be dangerous for PCs with active pfc.

it's safe to use a non sine wave UPS in the US, or any other country where the line power is 120VAC ...... But I also tried to make another important point, it is ONLY safe if you are using a APFC PSU, this is because then there is only ONE input capacitor and it will be rated at 450VAC If you are using a Passive PFC or non PFC PSU you will have TWO capacitors, and a selector switch for 120VAC or 240VAC operation These capacitors will be rated for only 200VAC EACH In a country where the line power is 120VAC only ONE of the capacitors will be used But the square wave voltage will in the US be 470VAC/2=235VAC So that's why you need a APFC PSU, APFC PSU=450V capacitor Passive or non PFC PSU operated at 120VAC = 200VAC capacitor, too little for 235VAC square wave

The explanation behind the danger was based on some oscilloscope readings the output of such UPS, which contain besides quite blocky, quite high peaks at the block edges, that may kill some caps.

  1. A general discussion on the topic of UPS and dangers to active pfc is interesting and can be found on many places, without a clear consensus (at least I didn't find it). So some clarification on that topic could be of interest, because conclusions seem controversial.

  2. But at this point my main question is, if putting a voltage regulator behind such as "modified sine" ups, could prevent the damage by such peaks to PSUs with active pfc?

  • @Sathya your edits removed some links to the references, i think the links are quite essential for the discussion. Thank you for your effort in editing, but i dont really consider the removing of the links and shortening of the quotes as improvements. Yes its shorter now, but less clear in my oppinion. – Sarmes Nov 19 '14 at 12:40
  • @Sathya Is the orriginal version of my post now completly lost, or is there some way how to retrieve it? – Sarmes Nov 19 '14 at 12:45
  • To my knowledge, the sine wave approximation only occurs when running on battery power. When the mains power is connected the output should be similar to normal AC. My UPS causes a buzzing sound due to sine wave approximation, but only if I disconnect the mains. If you buy a reasonable make and model (e.g. an APC SMART UPS, about $500) then I really don't think you should have any problems since people are using them all the time for critical situations. The cheap consumer voltage regulators you are talking about do not turn the input into a pure sine wave, they simply prevent spikes. – James P Nov 19 '14 at 12:49
  • there were 4 references when I started editing - they are still there - the http was left out, so the parser wasn't linking them. Corrected that. You can see all revisions at superuser.com/posts/842187/revisions – Sathyajith Bhat Nov 19 '14 at 12:49
  • @Sathya i see the links in the bottom when i edit, but i dont see them in the normal text. Whithout the links, people miss an important the point of the question e.g. James – Sarmes Nov 19 '14 at 12:52

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