In 1998, Ask Ars was an early feature of the newly launched Ars Technica. Now, as then, it's all about your questions and our community's answers. Each week, we'll dig into our question bag, provide our own take, then tap the wisdom of our readers. To submit your own question, see our helpful tips page.
The recent severe weather in the US has got me thinking about going above and beyond surge protectors to protect my computer. I'm thinking about getting a battery backup, but I don't know what I need to look for in an uninterruptible power supply.
If you are looking to protect your electronics—particularly your computer—from the bigger power anomalies in life, the run-of-the-mill surge protector just won't cut it. Surge protectors cover only one of the two common types of damaging power conditions, while an uninterruptible power supply can cover both.
Surge protectors are meant for over-voltage scenarios, when there's suddenly a surplus of power from a lightning strike or surge from your electric grid. Without at least a surge protector, surges and spikes can cause damage to your hardware; your computer or monitor might not die outright, but a sudden jump in voltage can be like a punch in the kidney.
What surge protectors are powerless to do anything about are under-voltage scenarios, when the voltage level from a power outlet sags. This is common in situations like during a heat wave, when a bunch of customers in a section of the grid turn on their air conditioners at the same time. This can cause a disturbance in your power source like a brownout or blackout, and it's just as bad for your components as a surge.
Uninterruptible power supplies (UPS), or battery backups, have a battery built in that can help bolster your voltage supply during under-voltage scenarios, as well as cut your electronics off from outlet power during a surge or spike. During these anomalies, the battery can support your setup for a short time, allowing you to carry on if the situation is short-lived, or pack it in and save all your work before powering down in a long-term blackout situation.
To choose a UPS for yourself, the figure on the packaging that you most need to pay attention to is the VA rating or wattage output that the unit is capable of. These numbers are related, but not interchangeable, so you'll need to establish the needs of your system in terms of one or the other.
Wattage is usually the easier figure to find for electronics, especially in data sheets or spec sheets published online. The safest thing to do is account for your components' maximum draw—for instance, a PC tower might average 250-300 watts, but if the power supply is capable of 500 watts, you should put the tower down for 500.
The VA (Volt-Amps) rating is a little harder to establish for some electronics: take the voltage in volts and current in amps, and multiply them together.
When you've determined all the pieces you want to protect or carry through power anomalies—PC tower, monitor, router, modem, speakers—add up their VA or wattage figures (but not with each other. Don't cross the streams). You want a UPS with ratings higher than that number, preferably by a margin of at least 20 percent. If you skirt the limit, you risk damage not only to your system, but also to the UPS you buy.
In the same vein, the larger a wattage or VA rating your UPS has, the longer it can power your system. Even for the largest of margins, you won't get more than a number of minutes of power out of a UPS, but if you typically work on complicated projects, it may be wise to opt for a UPS that will give you 15 minutes to finish up as opposed to 3 or 4. Some brands of UPS publish graphs on their product pages that let you see time estimates for how long a particular UPS can power your system given a certain wattage or VA. At the same time, don't get preoccupied with long uptimes—most outages (90 percent) are quick, while the rest tend to be quite long, so unless you really need it, that extra 8 or 10 minutes won't do you much good.
Once you have the VA or wattage figured out, you'll want to check that the UPS has the features you want. UPSes may seem to have an abundance of outlets, but usually half of them are only surge-protected. Printers and other less complex components will be fine in the surge-protected-only outlets, but anything that is more expensive or delicate that you might be hoping to use during a blackout for a few minutes can go into the backed-up outlets. The largest consumer UPSes seem to top out at 5 battery-backed-up outlets, so plan accordingly.
Most UPSes these days also have in and out ports for coaxial or telephone line plugs (RJ-45 and RJ-11). Power dips and surges can run through those sources too, so if you have a machine that uses them, it's a good idea to run those connections through.
Some UPSes also come with management programs that you can install (these communicate with the UPS via a USB connection) where you can tweak the voltage at which the UPS will kick in with battery support and other settings. Not all UPSes are compatible with all systems (e.g. APC UPSes don't officially support that interaction with Intel Macs), so pay attention to which OSes are supported if you want total control of your battery backup.
We do have one warning: don't plug laser printers into the battery-backed-up outlets in UPSes. You may be tempted if you love to print, but even small-scale laser printers can suddenly draw too much power when turning on or heating up to print, and it can damage the battery.
(Update: A few readers have requested a description of the difference between online, line-interactive, and standby UPSes. Standby UPSes are often the cheapest, and only step in when the power supply is fluctuating widely, often taking many milliseconds to do so. Line-interactive UPSes have transformers that can moderate small voltage fluctuations, usually between 100 and 140 volts, without using the battery, saving that power for larger-scale brownouts, blackouts, or surges.
Online UPSes are always modifying the power supply between the wall and connected devices and can smooth out the tiniest of fluctuations. For this reason, and because their batteries often have longer lives (standard UPSes need battery replacements every two or three years), online UPSes can be more expensive than the other two types. Most UPSes available at the consumer level are either of the standby or line-interactive variety.
Thanks to Mike Koenig and Flickr users Craig Key and daveiam for supplying thunderstorm video and sound.
reader comments
136