Why you should get an uninterruptible power supply

I thought I was ready for power outages. I had flashlights, a collection of charged power banks for my appliances, and the mental toughness to eat all the ice cream in the freezer before it melted. Even so, I was unprepared for a momentary drop in the voltage running through my house.

Last summer, during a heat wave, I was editing videos with no worries when it came time to render and compress 45 minutes of flawless content. I pressed the button to start the process when the lights flashed and my screen went dark. Like Icarus, I hadn’t factored in the oppressive heat of the sun, and the energy stress of everyone in the area blasting their air conditioning to avoid heat stroke had been too much for the grid to handle. While the effects of the brownout on the rest of my house were limited to a few minutes of dimming the lights, all the work I had done on my PC was shot. A process that would have been done that hour was not completed until the next day. What I needed was an uninterruptible power supply. Chances are you need it too.

What is that?

An uninterruptible power supply (UPS) is exactly what it sounds like. Essentially a surge protector combined with a battery and an inverter, it will protect your electronic devices from the perils of a sudden power loss or fluctuation. When the power goes out, the battery kicks in and the DC current from the battery is reversed to AC current that your electronic devices can use. This gives you plenty of time to save your work and shut everything down properly, or give low-power devices a few extra hours of life. The concept is quite simple, but finding the best inverter for your needs can be a challenge.

These power supplies can vary greatly in scale. On the low end, some provide just enough power to keep your modem and router running while you work on your laptop and wait for the power to come back on. On the high end, one can power the entire city of Fairbanks, Alaska in up to seven minutes. For the purposes of this article, we will assume that you are not working at the municipal level.

There are three basic types of UPS: standby, line interactive, and double conversion. Standby models simply switch to battery power as mentioned above, although their output is less consistent. In a standby UPS, power fluctuations above or below the desired range cause utility power to switch to the battery, which can take up to 25 milliseconds. These are suitable for devices that can sustain a split second of power outage without risk, such as modems, routers, and device power supplies with batteries. They can handle power outages, brownouts, and surges without incident.

A line-interactive UPS is best suited for most people’s needs, using automatic voltage regulation to counteract power fluctuations and provide stable current before switching to battery power. This means that during a brownout or surge, the internal transformer will continue to supply power at the appropriate level before switching to battery without delay. The increased ability to handle power dips means that’s what my computer would have needed to survive last summer’s heat wave.

And finally, unless you’re running a data center, you probably don’t need a double-conversion UPS. These models were once reserved for massive computer installations, but have since been scaled down to the consumer level. Although they have become smaller, their prices remain high. That said, a double-inverting UPS is the most stable of the three basic options because it never has to switch power sources. AC power goes directly to the battery, and battery power is converted back to AC power at all times. As its output is always derived from the battery, a power outage will have no effect on connected devices until the UPS battery is depleted.

So what do I need?

The average consumer should get an online interactive inverter. If you’re powering a PC or medical equipment, look for ones that have pure sine wave inversion, which provides a current indistinguishable from properly functioning household electricity. Some cheaper models use a simulated sine wave output, which will be sufficient to run simpler devices without incident, but will likely cause problems when using a PC or CPAP machine.

[Related: 4 things to do long before you lose power]

The most important thing to look for in any UPS is its power capability, as none of the other features matter if there isn’t enough power for the connected devices. A UPS that can keep a modem and router alive for several hours may only have enough juice to keep your PC and monitor on long enough to save and shut down. Check the volt-amps and wattage of the inverter against the power requirements of the devices you’ll be plugging into it to make sure it can handle the workload. Volt-amperes aren’t obvious on most devices, but can be estimated with a handy online calculator. Put the power of the device in the first box and 0.6 in the second, because UPS manufacturers’ industry standards assume a 60% power factor for common personal computer loads. Once you’ve figured out the volt-amps, err on the side of caution by getting an inverter that can handle at least 20% more. This extra capacity helps avoid potential overload, so you don’t burn your house down.

Speaking of burning down the house, there are a few other safety tips to keep in mind: Never plug a UPS into a surge protector or extension cord. Never plug a heater or anything with a powerful motor into the UPS, as this may overload the device. Read reviews and make sure the review you read specifies the horsepower capacity of the model in question. Check the reviews of any power inverters you view online to see if anyone is complaining that they burst into flames because they plugged in too many things, then don’t repeat their mistake. If in doubt, read the manual.

What uninterruptible power supply should I get?

We ran out of space for a full review, but our gear team has you covered for what they consider to be the best battery backups on the market. But we can provide a little primer. If you don’t need a pure sine wave for sensitive devices, the CyberPower CP1500AVR is a top choice. If you need enough power for your PC and monitors, the APC 1500VA Sine Wave UPS is our choice for networks that need lots of power and true sine wave output. No matter what you get, take careful notes and compare them to your needs to make sure your specs are covered. Then make sure you’re still looking at the corresponding model, because for all their wonderful utility, they’re all black boxes with deeply unforgettable names.

Alan A. Seibert