UPS Buying Guide: Protect PCs, Routers and CCTV from Power Cuts

A power cut in the middle of a document, a video call or a CCTV recording is more than an inconvenience. Sudden shutdowns can corrupt files and hard drives, and the voltage dips and spikes that often come with outages and thunderstorms can damage electronics. A UPS (uninterruptible power supply) bridges the gap. Here is how to choose the right one.

What a UPS does, and what it does not

A UPS contains a battery and an inverter. When mains power fails, it switches to battery so your equipment keeps running. Most models also filter surges, and many correct low or high voltage automatically without using the battery.

A typical UPS is not designed to run an office for hours. Small units give you minutes: enough to save work and shut down safely, or to ride through a short outage. For longer backup you need bigger batteries, an extended-runtime model or a separate inverter or generator system.

VA vs W: the number that matters

UPS models are named by VA (volt-amperes), such as 650VA or 1000VA, but your equipment draws power in watts (W). The two are linked by the power factor: watts = VA × power factor.

Many small line-interactive units have a power factor of around 0.5 to 0.6, so a 1000VA model may be rated for only about 500 to 600 W. Always check the watt rating on the specification sheet, and size by watts.

How to size your UPS

1. List what you want to protect. Check each device’s label or specifications. A power supply’s maximum rating is usually higher than what the device draws in normal use.
2. Add up the watts. As a rough guide, a router or fibre ONT uses around 10 to 20 W, an office desktop with a monitor often 100 to 200 W, and a gaming PC much more under load.
3. Add headroom. Choose a UPS with a watt rating at least 20 to 30 percent above your total. A UPS running near its limit gives very little backup time.
4. Decide how long you need. Manufacturers publish runtime charts showing backup time at different loads. Use them to compare models.

For a rough estimate: backup time in hours ≈ battery watt-hours (volts × amp-hours) × 0.8 ÷ load in watts. A single 12V 9Ah battery holds about 108 Wh, so a 50 W load gives about 1.7 hours by this formula. Real runtime is usually lower, especially at high loads and as batteries age, so treat it as a best case.

Types of UPS

Offline (standby)

The simplest and cheapest type. Equipment runs on mains power until it fails, then the UPS switches to battery after a short transfer time. Fine for a basic home PC where the voltage is stable.

Line-interactive

Adds automatic voltage regulation (AVR), which boosts low voltage and trims high voltage without draining the battery. It is the most common choice for home and office PCs, routers and small CCTV systems, and it suits areas where voltage drops in the evening.

Online (double conversion)

Equipment runs from the inverter all the time, so there is no transfer delay and the output stays clean whatever the mains supply is doing. Online units cost more, run warmer and usually have fans, but they suit servers, NAS units, network racks and sites that rely on a generator.

Type	Voltage correction	Switch to battery	Best for
Offline	None or basic	Short delay	Basic home PCs
Line-interactive	AVR	Short delay	PCs, routers, small CCTV
Online	Continuous	No delay	Servers, NAS, sensitive equipment

Pure sine wave or simulated sine wave?

On battery, cheaper models produce a stepped, “simulated” sine wave. Many modern PCs have power supplies with active PFC that work best with a pure sine wave, and some may shut down or buzz on a stepped output. For modern desktops, workstations and NAS units, a pure sine wave UPS is the safer choice.

UPS for routers and CCTV

• Routers and ONTs: a DC mini UPS that connects to the router’s power input can keep the internet on for hours, because the load is small. Check that the voltage and connector match.
• DVRs and NVRs: protect the recorder, the camera power supply or PoE switch, and the router, so recording and phone viewing continue.
• Night-time load: cameras draw more power when their infrared lights are on, so size for the night.

Look after the battery

• Sealed lead-acid batteries usually last a few years. Heat shortens their life, so keep the UPS in a cool, ventilated place, not a closed cupboard.
• Replace the battery when backup time drops noticeably or the UPS reports a fault.
• Do not plug laser printers, heaters, kettles or irons into the battery outlets. They draw far more power than a small UPS is built for.
• A UPS helps with surges, but it does not replace proper earthing and surge protection, especially in lightning-prone areas.

Frequently asked questions

What size UPS do I need for a home or office PC?

For a typical desktop, monitor and router, a 650VA to 1000VA line-interactive UPS is usually enough to save work and shut down. Gaming PCs and workstations need larger units, ideally with pure sine wave output. Always compare the watt rating with your total load.

How long will a UPS run during a power cut?

It depends on the load and the battery. A small UPS supporting a desktop PC usually gives minutes, while a DC mini UPS powering only a router can last hours. The manufacturer’s runtime chart gives the best estimate.

Can I use a UPS with a generator?

Yes, but generator output can vary in voltage and frequency. Online UPS units generally cope best, while some line-interactive models keep switching to battery on unstable generator power, so test the combination before you rely on it.

Browse our UPS and power backup range for PCs, routers and CCTV systems, or ask us to help size a unit for your equipment: call our Kandy team on +94 72 299 9915 or email info@eudora.lk.

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