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Frequently Asked Questions

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It’s a confusing world to navigate, and sadly often misleading. We make it simple for you.

We have answers to your most frequently asked questions below. Alternatively, just go to our Backup Power Finder, answer the easy questions, and we’ll take care of the rest. We’ll make sure you get the right UPS for you!

Both generators and a UPS’s are a reliable source of power when the main source of electricity experiences a blackout (e.g. Loadshedding) or brownout (sags, or even surges). Generators convert fuel to electricity when needed, and a UPS is essentially a system that allows you to store electricity to and retrieve electricity from batteries. They both have their advantages and disadvantages:

  • Generator: The biggest advantage is that they’re much more cost effective to power large appliances and large loads (when compared to UPS’s). They’re also relatively more mobile as they can be moved to where power is required. However, they need to be placed outdoors with adequate ventilation and security. They’re noisy, are expensive to run since they require fuel (petrol or diesel) and regular maintenance, and don’t automatically ‘kick in’ when the power goes out.
  • UPS: They don’t make a noise, and is suitable for indoor use. They’re relatively cost effective for small to medium loads (appliances) and their running costs are very low since they don’t require fuel. They have the added benefit of regulating the power seamlessly at all times, protecting your appliances from surges and sags and no ‘gap’ in downtime as in the case with a generator.

UPS stands for Uninterruptible Power Supply (UPS). It is a system that’s designed to keep the power running at all time even when the main power grid goes down (a blackout, or loadshedding), or during power surges or sags (a brownout). Depending on the size of the battery in the UPS, this can sustain power for a few minutes to allow you the time to safely shutdown appliances to prevent damage as a result of a sudden shutdown, or it can sustain power for hours to allow you to continue enjoying the use of appliances (such as watching TV).

A UPS performs two vital functions. It allows for energy storage while the there is a main power source, and then provides an instant response with electricity during a blackout or brownout providing uninterrupted electricity supply to all appliances connected to the UPS for a period of time (could be minutes, could be hours depending on the goal and size of the batteries). The critical components being:

  • Rectifier (Charger): Converts AC voltage to DC voltage, recharges the batteries and maintains float voltage, handles overloads and buffers surges, can accept wide input voltage fluctuations.
  • Battery: Provides emergency power source when mains supply fails.
  • Inverter: Converts DC voltage to AC voltage, regulates and filters AC voltage.
  • Static Bypass: Automatically connects load to mains supply if overload or fault occurs.

A UPS and an Inverter are often confused with each other. In simple terms, an inverter is a device that converts direct current (DC), such as a battery, to an alternating current (AC) supply that is suitable for appliances.

An inverter on its own can not generate or store electricity and hence cannot provide backup power without being coupled with other components such as batteries, etc. Therefore a UPS is a more complete solution for blackouts and brownouts and actually uses an inverter as one of its internal components. See sketch here “How does a UPS work?”.

UPS’s aren’t regulated in South Africa, and manufacturers and retailers make claims that are not always entirely truthful or can be misleading. Not all UPS’s are the same, even when they appear to be at first glance. This is precisely the reason we have developed this website and its accompanying quizzes and calculators. We aim to help you compare apples to apples and make an informed decision. When comparing UPS’s, there are the most important aspects to consider:

  • The Power Requirement: A UPS is often “sized” in terms of Wattage or Voltage, for example 2000 Watts / 2kW; or its equivalent Volt-Ampere 2000 VA or 2kVA. This is the capacity the Inverter is able to sustain at any point in time. This gives no indication of how long you can keep appliances running at all, it only indicates how many (or how much power you can sustain). Tip: Not all UPS’s are equally efficient. Since every UPS needs some electricity to power itself, it is important to only take into account the Real Power (in Watt). Since the metric isn’t expensive, we suggest adding at least 20% to your estimated load requirement when sizing the UPS.
  • The Type of Power Wave Supplied: However not all UPS’ supply power in the same wave format. Some offer an output of Stepped or Modified Sinewave, which is not suitable for some appliances. Other UPS’s supply Pure Sinewave, which is more expensive, but is the safest option to prevent damage to your appliances. Tip: When in doubt, rather be safe and opt for a Pure Sinewave UPS, or alternatively use our Quiz (click here) to find yourself the most suitable UPS at the best price.
  • The Battery Runtime during Outages: The battery runtime is one of the most crucial aspects when selecting a UPS, but also one of the most expensive and confusing components. And when something is confusing and expensive, there is a risk for people to be taken advantage of. The rule of thumb is that the higher Ah (ampere hour) rating of the battery(ies), the longer the runtime should be (all else equal). Tip: A battery lasts for progressively shorter periods of time as the load increases (called Peukert’s Law). This means that not all Ah ratings are done in the same conditions and hence you can’t just compare purely based on Ah ratings. Read our section that explains how battery backup runtime is calculate (click here) and use our calculator (click here) to ensure you’re comparing apples to apples.
  • The Switchover Time: This is the amount of time a UPS will take to switch from main power to battery power during a mains failure, or from battery to mains when normal power is restored. For very expensive, sensitive and mission critical equipment you ideally want this spec to be under 8ms (milliseconds).
  • The Maintenance: Connecting batteries in series will increase the voltage of the UPS. The increased voltage will double the backup power runtime of the batteries due to higher voltage, and reduce the heat generated inside the UPS which will increase the lifespan of components. Tip: Therefore it is better, for example, to pay a little more to have two batteries with 50Ah rating, than having one battery of 100Ah. The runtime will be the same, but your UPS will last longer.

There are generally three types of UPS’s. It is their components, and how they’re wired, that defines them:

  • Offline: This UPS offers the most basic features, providing surge protection and battery backup. It generally has a slower switchover time, and when the incoming voltage falls below or rises above a predetermined level the UPS turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. They’re the most cost-effective type of UPS on the market.
  • Line-interactive: This UPS has a quicker switchover time and has the benefit of having a Voltage Regulator. It can tolerate continuous undervoltage brownouts and overvoltage surges without consuming the limited reserve battery power. It instead compensates by automatically selecting different power taps on the autotransformer (adding or subtracting powered coils of wire, thereby increasing or decreasing the magnetic field and the output voltage of the transformer).
  • Online Double Conversion: The Online UPS doesn’t wait to kick in during a power cut, sag, or spike. In fact, it converts and stores all incoming power to the battery, and then in turn converts and feeds all appliances from the battery alone. Therefore this online UPS offers total electrical isolation for equipment that is very sensitive to power fluctuations. The initial cost of the online UPS may be higher, but its total cost of ownership is generally lower due to longer battery life.

It is a complex mathematical formula which includes many factors (not just Ampere and the Ah rating of the battery as many people may assume). We suggest using our calculator (click here) which needs to take the following into account:

  • Total Watts of Equipment: This is the total units of power required by all the appliances.
  • The Battery’s Ah (Ampere-hour): The takes into account the capacity of the battery which is measured in Ah (ampere hour). This is a function of ampere (current) the battery can offer, and time (numbers of hours). It’s an indicator, but not a rule for backup runtime (in hours)
  • How Many Batteries (Voltage): The more batteries connected in series, the higher the voltage. The higher the voltage, the less current is required to power a given appliance (Remember Watts = Volt x Ampere). So for example if you have double batteries (double the voltage), then each battery can be half the capacity (half the Ah).
  • Peukert’s Constant, and Rate of Discharge: This is a performance indicator of the battery. The Peukert constant indicates how well a battery performs under continuous heavy discharge current. Manufacturers specify the capacity of a battery at a specified discharge rate. For example, a battery might be rated at 100 Ah when discharged at a rate that will fully discharge the battery in 20 hours (at 5 amperes for this example). If discharged at a faster rate (e.g. 10Ah) the battery may only last 8 hours and hence the delivered capacity is less (in this case, 80Ah). Tip: So don’t always believe Ah ratings!

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