In my area, due to frequent storms, there are frequently short mains power cuts lasting a second or two at most. While the shorter several-millisecond outages don't usually cause issues, the longer momentary outages frequently cause my computer to shut off, resulting in filesystem corruption and other issues.

I want some type of system capable of providing around 600 watts for 2-3 seconds, just enough to hold the system over until mains power resumes. Ideally, this device would be small enough to fit inside my computer case.

The various UPSes available online are all either (a) really expensive or (b) not capable of providing the wattage I need. Besides, I don't need the hours or minutes one of those provides, just a few seconds.

I have considered just putting some supercapacitors between the power rails, but I think that could cause problems when starting up (the PSU would have to charge the capacitors, so the voltage would take much longer to reach the required supply voltage), during these momentary outages (not sure I want to be backfeeding power to the PSU, but I don't want to have to connect every line coming out of it), when shutting down (since they would continue supplying voltage), and during service (since things could potentially still be energized even after the PSU is unplugged). I have some ideas for how to solve some of these issues, but not all of them at once, and I am not sure this is the best way to solve this problem.

What is the best way to solve this problem?


closed as too broad by PeterJ, Daniel Grillo, Ricardo, Scott Seidman, JIm Dearden May 20 '15 at 17:02

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The BEST way to solve this problem is to get an AC mains UPS (uninterruptible power supply) that is able to supply AC power to your computer during momentary power outages.

You can get UPS units that can supply 650VA which should work nicely for your application that are less than $100. The beauty of these units is that you simply plug your computer into the UPS and then the UPS plugs into the AC mains.

I would strongly encourage you to stop thinking you can kludge together some type of home hack solution on the DC side of the supply. You will certainly spend at least as much in parts and the solution will be a hack at best -- if you know what you are doing when you built it.

  • \$\begingroup\$ This is hands down the "best way to solve this problem", but it's probably not the answer you're looking for. Even so, accept it; I think you'll benefit from a lot more experience before you tackle the build requirements for a UPS from mains. Not that I'm trying to 'scare' you away from mains/high-power levels, the people who do that are projecting their own inadequacies, just make sure you read up on it a LOT if you're going to do it yourself instead of buying it. \$\endgroup\$ – ARMATAV May 17 '15 at 16:23
  • \$\begingroup\$ I'd add that if you are going to use the UPS on very short outages you can probably buy something a little smaller. \$\endgroup\$ – Vladimir Cravero May 17 '15 at 19:18

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