UPS (Uninterruptible Power Supply): How to choose the right uninterruptible power supply.

UPS (Uninterruptible Power Supply): How to choose the right uninterruptible power supply.

An uninterruptible power supply ( UPS ) is a device that keeps your devices running when there is a power outage and, at the same time, protects against voltage spikes and variations . For those who work from home, have a NAS, consoles, router/ONT, IP cameras, or a small office, a UPS is one of the "cheapest" purchases compared to the cost of losing data, burning out a power supply, or being without internet at the worst possible time.

Below you have a practical (and uncomplicated) guide to choosing a UPS in Brazil: what type to buy, how to size VA vs. Watts, how to estimate runtime, when you need a pure sine wave, and how to care for the battery .

What a UPS actually does (and what it doesn't do)

An uninterruptible power supply (UPS) is used for:

  • Maintain power for a few minutes (to save work, safely shut down, or "endure" short outages)

  • Filter/protect against surges and fluctuations (depending on the model/topology)

  • In many models, correct voltage drops/surges without draining the battery (AVR).

"Classic" uninterruptible power supplies (UPS) are not designed to keep the entire house powered for hours—the goal is usually to save time . A common reference point is that a typical battery provides 5 to 15 minutes of runtime , and those who need more use external battery modules .

Types of uninterruptible power supplies (UPS) (topologies): offline, line-interactive, and online.

The IEC 62040 standard distinguishes three main UPS modes/topologies: passive standby (offline) , line-interactive , and double conversion (online) .

1) Offline / Standby (the basics)

  • Cheaper

  • In the event of a power outage, it switches to battery power and provides additional power.

  • Good for: simple uses, insensitive loads

2) Line-Interactive (the “best cost/benefit” option for home use)

  • Very common in home and small office UPS systems.

  • It usually includes AVR (automatic voltage regulation), which corrects variations without using a battery.

  • Good for: PC, router/ONT, NAS, console, TV, small networks

3) Online / Double-Conversion (professional level)

  • The load is continuously powered by the inverter (power is always "conditioned").

  • Improved protection against electrical disturbances and greater stability for critical loads (servers, sensitive equipment, telecom).

  • More expensive and, in many cases, with a fan (noisy).

Simple rule for buying:

  • Home and home office → typically Line-Interactive

  • Critical servers/"poor" electrical environments → consider Online

Pure sine wave: when is it mandatory?

You will see UPS with:

  • pure sine wave

  • simulated sine wave (stepped/simulated sine wave)

For modern equipment with active PFC (many gaming PC power supplies, workstations, and some servers), the recommendation is to opt for a pure sine wave , because it improves compatibility and stability when the UPS is operating on battery power.

When I recommend "pure sine wave" without much thought:

  • Gaming PC/workstation with modern power supply (active PFC)

  • NAS + switch + router with significant continuous load.

  • Sensitive and expensive equipment that you want to protect seriously.

VA x Watts: How to size your UPS correctly

Here's the number one mistake people make when buying UPSs: only looking at " VA " and ignoring " Watts ".

  • Watts (W) = actual power consumed

  • VA = apparent power

  • Relationship: W = VA × PF (power factor)

Eaton explains that real power (W) is related to VA through the power factor (PF) , which ranges from 0 to 1; in many modern IT devices, the typical PF is ~0.9 or higher .

Step by step (quick and safe)

  1. Add up the wattage of the equipment plugged into the UPS.

  2. Adds 25–30% margin (peaks, growth, efficiency)

  3. Make sure the UPS supports both Watts and VA !

Practical examples (so it doesn't stay just theory)

Example A — Router + ONT + Wi-Fi Mesh (internet during power outages)

  • Router 10 W + ONT 10 W + Mesh node 10 W = 30 W

  • With a 30% margin → ~40 W
    ➡️ A small UPS may be sufficient — and often provides ample backup power because the load is low.

Example B — Gaming PC + monitor (you want to save and shut down calmly)

  • PC in use: ~450W (varies greatly)

  • Monitor: ~40 W
    Total: 490 W
    With a 30% margin → ~640 W
    ➡️ Looking for a UPS that supports ≥ 640 W (not just VA).
    If PF ~0.9, 640 W ≈ 711 VA (W/PF), but in practice choose with a margin (for example, 1000–1500 VA) to have decent autonomy and avoid stress.

Example C — NAS + switch + router (data protection)

  • 60W NAS + 15W switch + 10W router = 85W
    With margin → ~110 W
    ➡️ A "medium" UPS (Uninterruptible Power Supply) can handle the load well and provide enough time for the NAS to automatically shut down.

Autonomy: how long can a UPS really last?

Autonomy depends on three things:

  • battery size/condition

  • UPS efficiency

  • connected load (W/VA)

Eaton offers a useful rule of thumb: by reducing the load, battery life increases significantly; and many users look for something like 7–10 minutes to cover short interruptions and allow for safe shutdown.
Generally, a typical UPS battery provides 5–15 minutes of runtime, which can be extended with external batteries in models that support it.

A very practical tip: buy UPS units that meet your actual needs.

  • To avoid wasting work , 5–10 minutes is usually enough.

  • To keep internet and cameras running → you often want 20–60 minutes (low battery helps).

  • To "stand by generator" → you may need more, or a system with external batteries.

Outlets, connections, and details that make a difference.

Before you buy, check:

  • Socket type : Schuko (F) vs IEC (C13/C14)

  • How many outlets are battery powered and how many are just "emergency protection"?

  • If you have a USB port for communication with a PC/NAS (automatic shutdown)

  • Does it support network card/management (SNMP) in professional configurations (some use slots like SmartSlot)?

Warning: Very low load may cause some UPS systems to shut down.

In certain "domestic" models, there is a no-load shutdown function: if the current consumption is very low (e.g., less than ~15 W), the UPS can shut down on battery power.
If your goal is to keep only the router/ONT powered, choose a UPS that handles low loads well or allows you to adjust this function.

What equipment should you NOT plug into a standard UPS?

Avoid connecting (especially to small UPSs):

  • heaters, kettles, microwaves

  • dryers, irons, resistive appliances

  • laser printers (high peaks)

An uninterruptible power supply (UPS) is for electronics and mains power , not for loads that draw a lot of power.

Batteries: lifespan, temperature, and maintenance

Most home UPS (uninterruptible power supply) systems use VRLA (sealed lead-acid) batteries. A well-cited rule of thumb is that the expected lifespan is usually 3 to 5 years under recommended conditions.

Temperature is the "silent killer"

Schneider/APC itself indicates that the ideal temperature for lead-acid batteries is ~20–25°C and that each increase of ~8°C can cut the lifespan in half (e.g., 4 years at 25°C can become 2 years at 33°C).
Eaton also reinforces the same principle (above 25°C, lifespan decreases significantly).

Best practices:

  • Do not place the closed UPS on hot furniture.

  • It maintains ventilation and avoids direct sunlight.

  • Perform regular battery checks and don't ignore low battery warnings.

Shopping checklist (Portugal): you choose in 60 seconds

  1. Objective : Save PC? Keep internet? NAS? Cameras?

  2. Topology : Line-Interactive (general) or Online (critical)

  3. Power : provides W and VA (with 25–30% margin)

  4. Pure sine wave : if modern PC/active PFC or sensitive equipment

  5. Autonomy : target 7–10 min before shutdown, or longer if needed.

  6. Connectivity : USB/SNMP if you want automatic shutdown/management.

  7. Battery : consider replacement (3–5 years) and temperature.

FAQ

Which UPS is better for home use: offline or line-interactive?
For most homes, line-interactive tends to be the best balance, especially because of the AVR (corrects voltage without draining the battery).

Do I need a pure sine wave?
If you have a modern PC (active PFC) or want maximum compatibility in battery mode, then yes — “pure sine wave” is the safest option.

How do I know how many VAs I need?
Take a portion of your power consumption in watts and consider the power factor (W = VA × PF). This way you avoid buying a UPS with high VA but low Watts.

How long does an uninterruptible power supply (UPS) last?
It depends on the load, but it's common to say 5–15 minutes as a reference for typical batteries; for longer charging times, some models accept external batteries.

How many years does the battery last?
Under recommended conditions, typically 3–5 years ; heat greatly reduces the lifespan (above 25°C, each ~8°C drop can cut it in half).

I want to keep only the router/ONT connected. What precautions should I take?
Some UPS systems may shut down if the load is too low (e.g., below ~15 W) due to a "no-load shutdown" function. Check this for the model you choose.