An uninterruptible power supply may be the least glamorous part of your computer set-up, but it’s a valuable one. It can save your system from both data loss and physical damage.
A UPS serves two functions. First, as the name implies, it provides battery power when line current fails. Second, it provides surge protection. It’s common for some outlets provide only surge protection without battery backup.
When the lights go out
A power outage of even a second is enough to stop your computer. Any work you haven’t saved is lost. Computers cache data for speed, so even data which you think you’ve written to disk might only be in the cache. When the power fails, it’s gone.
Power loss can affect not just the work you’re doing but your whole file system. A file directory consists of pointers to information about files, and each file is built out of pointers to data blocks. The information is scattered all over the disk, and if the pointers are wrong, the file is corrupted. Pointers might point to old, deleted data or to parts of another file. If the power fails in the middle of a file update, multiple files and even whole directories could be damaged.
A UPS gives you time to shut down your computer cleanly. You can save your work and run a normal shut-down, so everything is safe. You might want to file a power outage report first since your computer is still working in the dark.
Power outages often come with surges. A severe voltage spike can kill a computer. A UPS with surge protection will stop all but the most severe surges. It only has to do this once to pay for itself.
Some outlets on a UPS may have only surge protection. You can plug printers, scanners, and other devices that don’t need continuous power into them. When the power fails, they won’t needlessly draw battery power away from your computer.
It’s common for a UPS to provide surge-protected telephone jacks and USB charging ports as well as 230V outlets. This extends protection to all your devices.
Choosing a UPS
The range of UPS models is broad. Some are for business use and will keep several computers going for an hour or more. Others are less expensive and will let you shut down a home computer safely.
You’ll see a VA (volt-amp) rating as well as a watt rating in the specifications. Since watts are volts multiplied by amperes, this may sound a bit confusing. The watt rating is the amount of power the unit can deliver. The VA rating is the “apparent power” which a device uses. It’s usually higher than the watt rating and never lower. To be conservative, you should get a UPS with a watt rating high enough to power all the devices that plug into it. If you see only a VA rating, the watt rating is usually 60% of it.
The battery capacity tells you how much power it can deliver. How long it will last depends on the power that your devices draw. Battery capacity is measured in ampere-hours (AH). Often you’ll see an estimated runtime for a given number of watts drawn rather than an AH rating, which saves you some calculations.
Like any other piece of equipment, an uninterruptible power supply has a finite life. A battery’s capacity decreases over time, and the lifespan of surge protection depends on the number and severity of the spikes it has to handle. It may still seem to work, but an excessively old UPS could disappoint you when you need it. If you have one that’s more than five years old, it’s time to think about replacing it with a new model. If you don’t have one, think about adding one. It’s an investment in the safety of your computer and data.