Uninterruptible Power Supply (UPS) – The Definitive Guide

Uninterrupted Power Supply (UPS) - The Definitive Guide

The Uninterruptible Power Supply (UPS) has quickly become part-and-parcel of life in South Africa. Since the first announcement of ‘load shedding’ in 2008, UPS systems have been adopted into many households. The devices protect valuable electronics from electrical surge/outage damage and have saved families from countless headaches. Find out everything you need to know. (This green property feature is one of the best ways to keep long term tenants happy too!)

How Long Can a UPS Provide Power?

The power provided by a UPS system can last as long as there is charge in the batteries… This will depend on the home’s power draw, appliance usage and of course the capacity of the batteries themselves. An important thing to remember is that lead acetate batteries have limited lifespans. The service life of these batteries is measured in cycles (from full charge to depletion) until they are only able to provide half of their rated power output. A high quality lead acetate battery can have a service life of 1500 cycles @ 50% DOD.

With load shedding in its 14th year (at time of writing) an uninterrupted power supply is essential.
With load shedding in its 14th year (as of 2022) an uninterrupted power supply is essential.

What Are the Different Types of UPS?

There are 3 different types of uninterrupted power supplies:

Offline UPS

This is the most basic type of UPS system available. These UPS systems immediately switch on when they detect an interruption in municipally supplied power (for example during load shedding). These systems can provide power to a number of appliances in the home during scheduled load shedding or during unscheduled blackouts. In the event that mainline power is lost or anomalous, the system switches over to battery power.

Online UPS

Sometimes called “double-conversion” systems - these modules intercept mainline power and convert it from Alternating Current (AC) to Direct Current (DC) before converting the DC back into usable AC. The benefit of this double conversion is that the output current is perfectly rectified - virtually all power disturbances such as sine wave distortions are eliminated. This ensures that even the most sensitive electronics are protected at all times regardless of grid-power quality.

Line Interactive UPS

Line interactive UPS systems are sometimes referred to as ‘hybrid’ because they combine elements of offline and online systems. These systems are also able to condition mains power output before it is fed into appliances, however instead of using a Parallel Flange Channel (PFC) Block, they typically use an electrical switch block. This helps to maintain a standard of output power quality but is not able to produce perfect wave forms in the same way that double-conversion systems do. It is however sufficient for almost all domestic applications bringing a lower cost with added power quality.

Power Disturbance Offline vs Line Interactive vs Online UPS:

Power DisturbanceOfflineLine InteractiveOnlinePower failureYesYesYesPower sagYesYesYesPower surgeYesYesYesUnder-voltage YesYesOver-voltage YesYesElectrical line noise  YesFrequency variation  YesSwitching transient  YesHarmonic distortion  Yes

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Having an uninterruptible power supply will protect your home office from power surges and more.

What NOT to Plug Into Your UPS

Some of the most common household appliances should not be plugged into a UPS system. This is because their average draw is very high and can put strain on the UPS potentially damaging it.


Heaters can draw anywhere from 2000 Watts for a simple fan heater.


Toasters draw a lot of power too - a simple 2 slice toaster can draw around 1000 Watts with 4 slice variants drawing up to 1750 Watts.

Vacuum cleaners

The average vacuum cleaner designed for home use draws around 1200 Watts.

How to Choose the Right UPS

Choosing the right UPS for your needs may seem daunting… But thanks to Inpower’s Backup Power Calculator it’s never been easier.

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