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Do-it-yourself UPS

Posted by michael on from the shocking-experience dept.

Giampiero writes "Over at dansdata.com some guy named Dan creates a UPS out of some spare parts. To sum it up, "if you're looking for an industrial-capacity UPS solution, and don't like the prices of the off-the-peg options, it might be easier than you think to roll your own."" Of course you can mentally substitute U.S. 110 volts for Australian 220 volts wherever necessary...

4 of 388 comments (clear)

  1. Why convert DC to AC to DC? by cyberformer · · Score: 4, Interesting
    A major part of the description on the site (and the cost of a "real" UPS) is how to convert the DC output of a UPS to the AC power required by most PCs.

    Of course, PCs don't actually use AC power: there's a big box in the back that converts all the AC input back to DC. So why not save some money and bypass this, by running the PC straight off the battery (like a laptop)?

    1. Re:Why convert DC to AC to DC? by steveha · · Score: 5, Interesting

      I have, for years, wished for a DC input on the PC's power supply, and a standard for UPSes that would plug in to that DC input.

      Taking DC, converting to AC so the PC power supply is happy, then the power supply converts to DC... it would be nice if it could just be DC all the way.

      The problem is that your monitor, modem, etc. all expect AC power. It's easiest just to make a UPS that provides standard AC power, and plug everything in.

      Someday, I think we will have "smart" plugs. Wall power outlets will not be live by default; they will only serve power when a proper coded request goes in over a smart plug. The device will be able to tell the wall outlet what kind of power it wants, and the outlet will be able to tell the device what kinds of power it can offer. Then little kids will stick butter knives into wall outlets and not get fried; PCs and monitors will ask for +5 and +12 volts DC and get it; and UPSes will be able to feed +5 and +12 volts DC to those PCs and monitors.

      Actually, if you have the complicated smart power system I envision, there will probably be a UPS integral to the system. When your home loses power, the smart power system would broadcast a "power interrupted" signal and devices like your refrigerator and your laser printer will power themselves down; your PC will run for about 5 minutes and then power itself down (unless you are there and override it) and medical devices will run indefinitely. Maybe only the DC devices in your home will be on the UPS by default?

      steveha

      --
      lf(1): it's like ls(1) but sorts filenames by extension, tersely
  2. UPS maintenance by PD · · Score: 3, Interesting

    These do-it-yourself UPS thingies are going to require maintenance. Car batteries are designed to deliver about 3400 amps directly into the alternator of a car, only during the time that you turn the key. They they trickle charge very slowly off the engine mains.

    By contrast, UPS batteries are designed to discharge at a slower rate, but charge very very quickly to be able to work if the power suddenly cuts out two or more times in a row.

    The problem with using one battery where another is required is that a memory effect can develop. That slow discharge on a car battery can cause it to lose capacity and in as little as 6 months it'll be useless for any power failures over about 5 seconds.

    How much does a car battery cost? about $50. But, you're going to need one every 6 months or so, making a home built UPS actually many times more expensive than one you buy at Comp USA.

    I know it's counter-intuitive, but many things about batteries are.

    --
    If tits were wings it'd be flying around.
    1. Re:UPS maintenance by Compuser · · Score: 3, Interesting

      As a physicist I had to design a portable
      experiment. Imagine an industrial table
      full of physics equipment. It drew more power
      than any desktop or small server but needed
      to run for hours. We bought a single AGM sealed
      valve regulated deep cycle battery for $80 and
      it has worked well. It provided power continuosly
      for more than 4 hrs and as far as we can tell
      has not lost much capacity yet (i.e. after a few dozen fairly deep discharge cycles). It has also
      worked for a couple of years now without a hickup.
      So from personal experience, this scheme works
      very well, but a quality setup will run you ~$300.
      Look at boating and RV sites and newsgroups for
      names of good battery manufacturers and compare
      prices. We have nothing but good things to say
      about Concorde's Chairman batteries.