Sam Doran

My little corner of the Internet

Getting the right UPS

A UPS is a rather mundane device that you’ll be very thankful for one or two times a year. A properly sized UPS will keep your devices running through a minor power blip or cleanly shutdown your computer if your power is out for too long. It can also serve as a giant power reserve for charging mobile devices during an extended power outage.

A UPS is nothing more than a giant battery with some smarts to switch to battery power when it looses input power. In order for the UPS to function properly, it must be able to supply enough power to keep your devices running. But how do you determine the right size? Adding up the value printed on the power supplies of your devices will result in a UPS that is much too big (and expensive). The best method is to actually measure the power your devices are consuming using a Kill A Watt. Plug all your devices into a power strip, then plug the power strip into the Kill A Watt. Press the “Up” button until the display shows Watts and you’ll get an instant reading of the power consumption. This is the number you’ll want to use when shopping for a UPS1.

One further recommendation I would make if you’re using the UPS with a computer is to turn the monitor brightness all the may up and max out all your CPU cores to 100%. This will ensure your UPS can hold up even when you’re using your computer at full bore.

Turning the monitor brightness to 100% is pretty self-explanatory but maxing out all CPU cores isn’t quite so obvious. There is a handy command line tool called yes that will easily max out one CPU core. Run one instance of yes per core and you’ll get a very good idea of just how much juice your CPU can consume.

    # Background one yes per core
    yes > /dev/null &

    # This will max out four cores
    yes > /dev/null & yes > /dev/null & yes > /dev/null & yes > /dev/null &

    # When you're all done, stop them all
    killall yes

Once you find the appropriate UPS size and get it connected properly (make sure you connect to the Battery and Surge outlets not the Surge Only ones), it’s important to test your UPS. Once a month when you’re not doing anything critical, go ahead and yank the UPS plug out of the wall to simulate a power failure. Let it run for a few minutes, then plug the power back in. Most UPSs perform a self test once a week or so, but I like to do the manual test just for my own edification.

My two cents on which UPS you should buy is stay away from APC and buy a CyberPower. Lots of people swear by APC but my experience with their Back-UPS series has been abysmal. I also inherited many APC Smart-UPS at work and I’m not a fan of those either.

Despite the cheesy name, CyberPower makes a very good UPS. I like the PFC Sinewave series. They are super quiet when running on battery power unlike most APC units that emit an annoying buzz and have a loud fan. Plus they don’t use a proprietary cable for communication with your computer like APC does (can you tell I really don’t like APC UPSs?). The 1350 and 1500 models have USB ports for charging. They output 5VDC at 1A which will charge any mobile device2. This is great to have during extended power outages.


  1. Most UPS vendors like to publish numbers in Volt-amperes (VA) beacuse the number is bigger than the Watt rating. This measurement is confusing because of the Power Factor. Without getting into too much electrical engineering minutia, the power factor varies based on the power supply design, not the UPS. The watt measurement accounts for the power factor (because the Kill A Watt measures it) and is generally less confusing.

  2. The charger that comes with the iPad outputs 2A. An iPad will still charge at 1A but it will take longer to reach full capacity.