Uninterruptible Power Supplies: Standby, Line-Interactive and Online UPS — Which Your Computer Needs and How to Get the Capacity Right

In Tbilisi, brief power cuts and voltage surges are not unusual, especially in older buildings, in bad weather and at peak times. Every cut means the computer restarting, unsaved work lost and a risk to the file system — and strong surges can burn out a power supply, router or hard drive. An uninterruptible power supply (UPS) protects against these problems. But UPS units vary a great deal, and the wrong one may fail you when it matters. Let's look at the types of UPS and how to choose the right one.

What a UPS does

A UPS sits between the wall socket and the computer. While the mains voltage is normal, it passes it through to your equipment and charges its battery. When the power drops out or goes outside acceptable limits, the UPS switches to battery power in a fraction of a second. That gives you time to save your work and shut the computer down properly — or rides out a short cut without you noticing at all. It's important to understand that a UPS isn't designed to run a computer for hours without mains power; its job is to ride out short interruptions and give you time to shut down cleanly.

Standby (off-line) UPS

The simplest and cheapest. In normal operation the equipment is powered straight from the mains, and when the power drops out the UPS switches to battery. There's practically no protection against small voltage fluctuations: with frequent dips the UPS keeps switching to battery and wears it out quickly. Suitable for a router and a simple office computer where the mains is stable.

Line-interactive UPS

The most popular type for home and office computers. A built-in automatic voltage regulator (AVR) evens out high and low voltage without switching to battery. That's especially valuable on mains supplies with dips and surges, as in many parts of Tbilisi. The best choice for most computers, gaming systems, NAS units and network equipment.

Online (double-conversion) UPS

The equipment is always powered by the UPS's inverter: the incoming voltage is first converted to DC and then back to AC of a perfect shape. Switching to battery happens with no gap at all, and the output is clean, stable voltage regardless of the mains quality. These units are more expensive, noisier and give off more heat. They're needed for servers, medical and measuring equipment and workstations where an interruption is unacceptable.

Output waveform

On battery, inexpensive UPS units output a stepped voltage — a "simulated sine wave". Modern computer power supplies with active power factor correction (active PFC) sometimes don't work well with it: the computer switches off at the moment of switching to battery, or the power supply hums. For powerful and gaming computers with quality power supplies, choose a UPS with a pure sine wave output.

How to calculate capacity

UPS capacity is given in volt-amperes (VA) and watts (W), and the watts figure is usually noticeably lower. Go by the watts. Add up the real consumption of everything that will be connected to the UPS — the computer, monitor, router — and add 20–30% headroom. An office computer with a monitor usually needs a 600–850 VA UPS; a gaming computer with a powerful graphics card needs 1200–1500 VA or more with a pure sine wave. Don't connect a laser printer to a UPS: when printing it draws a very high peak current and can overload the UPS.

Runtime

Battery runtime depends on the battery capacity and the load. A typical home UPS keeps a computer running for 5–15 minutes — enough to save your work and shut down. For a router and network equipment, which use little power, the same UPS can keep the internet going for an hour or more. For longer autonomy there are models with external batteries, but for cuts lasting hours it's more sensible to consider a generator or an inverter with large batteries.

Maintenance and batteries

UPS lead-acid batteries usually last 3–5 years, and less in a hot room. When the battery is worn, the UPS may shut off at the first interruption even though the indicators look normal. Many UPS units can run self-tests and warn you when the battery needs replacing. A swollen, hot or smelly battery is a reason to disconnect the UPS immediately.

Automatic shutdown

Most UPS units connect to the computer with a USB cable. With the manufacturer's software or Windows' built-in tools, the computer saves its data and shuts down properly by itself when the battery runs low — even if you're not there. This feature is especially important for NAS units and servers.

What our technician does

1. Assesses the quality of your mains supply and your equipment's power draw.
2. Selects the UPS type and capacity with the right output waveform.
3. Connects the computer, monitor, router and NAS to the UPS correctly.
4. Sets up automatic clean shutdown and notifications.
5. Checks and replaces worn batteries and tests the UPS under load.

A real example

The owner of a small accounting office in Chugureti bought an inexpensive UPS, but at the very first power cut the computer with the 1C database shut down instantly, and the database had to be restored. Our technician found two causes: the battery of the UPS, which had sat in a warehouse for a long time, was worn out, and the UPS itself, with a simulated sine wave, didn't suit a power supply with active PFC. We installed a line-interactive UPS with a pure sine wave and the right capacity, connected the computer, monitor and router to it and set up automatic shutdown. Now short cuts pass unnoticed, and in longer ones the computer shuts itself down cleanly.

Call a technician

If your computer switches off during power interruptions or you want to protect your equipment from surges, we'll come to any district of Tbilisi around the clock. Learn more on our computer keeps restarting, component upgrades and electrician services pages.