UPS Buying Guide

An Uninterruptible Power Supply (UPS) is one of the most important — and most overlooked — components in any IT infrastructure. It is the last line of defence between your equipment and a power grid that, in South Africa, is anything but reliable. Load shedding, voltage surges, lightning strikes, and grid instability cause more data loss and hardware damage than almost any other single factor.

This guide covers everything you need to know to select, size, and operate the right UPS for your environment — from a single desktop to a full data centre.

1. What is a UPS?

A UPS is far more than a "battery in a box." It is an integrated power management system that combines:

• ›A battery (or battery bank) that provides power when the mains fails
• ›A rectifier/charger that keeps the battery topped up during normal operation
• ›An inverter that converts battery DC power back to AC for your equipment
• ›Surge and spike protection circuitry
• ›Voltage regulation to smooth out power quality problems before they reach your equipment

Under normal conditions the UPS passes mains power through to your equipment while keeping its battery charged. When power fails or degrades, it switches seamlessly — in milliseconds — to battery power, giving you time to perform a graceful shutdown or ride out a brief outage entirely.

2. Power Threats — What a UPS Protects Against

3. UPS Topology — The Three Types

Not all UPS systems work the same way. The topology determines how much protection your equipment receives and how quickly the UPS responds to a power event.

4. Sizing Your UPS — VA, Watts, and Load Calculation

Correct sizing is the most critical decision when buying a UPS. An undersized UPS will either shut down under load or provide dangerously short runtime.

VA vs. Watts

• ›UPS capacity is rated in VA (Volt-Amps) and Watts. These are different — a 1000VA UPS does not deliver 1000W of usable power.
• ›The relationship between them is the power factor. A UPS with a power factor of 0.9 rated at 1000VA delivers 900W of real power. Most modern UPS systems have a power factor of 0.8–0.95.
• ›Always size your UPS based on Watts, not VA. Add up the wattage of every device you will connect, then add 20–25% headroom.

How to Calculate Your Load

• ›Check the power consumption (in watts) of each device on its label, datasheet, or spec sheet.
• ›Add the wattage of all devices you will connect to the UPS simultaneously.
• ›Multiply by 1.25 (add 25% headroom) to arrive at your minimum UPS watt rating.
• ›Do not connect devices whose total wattage exceeds 80% of the UPS's rated watt output. Running at higher loads shortens battery life and reduces runtime significantly.

5. Runtime — How Long Will It Last?

Runtime is the duration the UPS can power your equipment on battery after mains fails. It is determined by battery capacity versus load — more load means shorter runtime.

• ›For graceful shutdown: You need 5–10 minutes — enough time to save work and shut down servers cleanly. Most standard UPS units at 50% load provide this.
• ›For load shedding: You need 30 minutes to 2+ hours to ride out a full stage of load shedding. This requires either a larger battery capacity or extended battery modules.
• ›Extended battery modules (EBM): Most enterprise UPS units support external battery packs that connect to the UPS to extend runtime without changing the UPS itself. Always plan for EBM compatibility when buying for load shedding environments.
• ›Reduce load to extend runtime: Only connect devices that must stay on during an outage. Move non-critical devices (monitors, printers, chargers) to a separate circuit not protected by the UPS.
• ›Battery age matters: UPS batteries degrade over time. A battery at 3 years old may provide only 60–70% of its original runtime. Most VRLA (sealed lead-acid) batteries should be replaced every 3–5 years.

6. Tower vs. Rack-Mounted UPS

7. Battery Technology

8. Key Features to Look For

• ›AVR (Automatic Voltage Regulation): Corrects brownouts and overvoltage without switching to battery. Essential in South Africa where voltage fluctuations are common during load shedding switchover.
• ›LCD display: Shows input voltage, output voltage, load percentage, battery charge, and estimated runtime. Invaluable for monitoring and diagnosing power quality problems. Look for models where the backlight can be dimmed for office environments.
• ›USB / network management card: Allows the UPS to communicate with a server and trigger an automatic graceful shutdown when battery reaches a threshold. Essential for unattended servers. Network cards allow remote monitoring across multiple UPS units.
• ›Hot-swappable batteries: Allows battery replacement without powering down connected equipment. Critical for servers that must remain online during maintenance.
• ›Surge-only outlets: Some UPS models include outlets that provide surge protection only (no battery backup). Use these for monitors, printers, and chargers — devices that can lose power without data loss — to preserve battery runtime for critical devices.
• ›Bypass switch: Allows the UPS to be serviced or replaced while equipment remains powered from mains — available on higher-end units. Essential for environments requiring zero downtime.
• ›EBM compatibility: Ensure the UPS supports external battery module connection if you need extended runtime for load shedding. Not all UPS units support EBM — check before buying.

9. Voltage and Frequency — South African Standards

• ›South Africa standard: 230V AC, 50Hz. Ensure your UPS is rated for 230V input and output — not the 120V units common in North American equipment.
• ›Input voltage range: A wider input voltage range means the AVR can correct more severe brownouts before switching to battery. Look for a range of at least 160V–280V input for South African conditions.
• ›Pure sine wave output: Active PFC (Power Factor Corrected) power supplies in modern servers require a UPS that outputs pure sine wave on battery. Stepped approximation or simulated sine wave UPS units can damage or cause instability in these PSUs.
• ›Outlet type: South African UPS units should have Type M (16A) or Type N sockets. Verify socket type matches your equipment's plugs before purchasing.

10. UPS Maintenance and Battery Replacement

• ›Test your UPS regularly: Perform a manual battery test at least once every six months. Most UPS management software includes a self-test function. Never assume the battery is good because it has not alarmed.
• ›Replace batteries proactively: Do not wait for a battery failure alarm to replace batteries. If your UPS is 3–4 years old and batteries have not been replaced, schedule replacement. A failed battery during an outage provides zero protection.
• ›Temperature affects battery life: Every 8–10°C above 25°C operating temperature halves the battery's service life. Keep your UPS in a cool, ventilated environment. Do not install UPS units in sealed, unventilated cabinets.
• ›Use manufacturer-approved replacement batteries: Third-party batteries may not match the exact specifications required by your UPS. Using incorrect batteries can affect runtime, damage the charging circuit, and void your warranty.
• ›Dispose of batteries responsibly: Lead-acid batteries are hazardous waste. Return them to a certified recycler or your UPS supplier for proper disposal — do not throw them in general waste.

Summary Checklist