How To Know What Size UPS You Need?

Understanding the Terminology

When selecting a UPS system, it is important to have a clear understanding of the terminology related to power capacity. Typically, the power capacity of systems is expressed in kilowatts (kW) and/or kilo-volt-amperes (kVA). For example, a 1 kVA UPS has the capability to handle 1,000 volt-amperes.

Power Calculation and Factors

In AC power, the formula "watts = volts x amps" seems straightforward. However, UPS systems have inherent inefficiencies due to transformers and circuitry, known as reactance. To account for these inefficiencies, UPS manufacturers specify a "power factor" that is used to calculate the maximum wattage the UPS system can handle. Thus, the formula becomes: watts = volts x amps x power factor.

For instance, a 1kVA UPS from N1 Critical Technologies has a power capacity of 900 watts for connected equipment, indicating a power factor of 0.9.

Optimal Utilisation and System Lifespan

Operating a 1 kVA UPS at 900 watts, or 100% of its capacity, is not recommended as it can lead to system failure in the event of a short circuit. To ensure proper functionality and longevity of the UPS, it is advisable to operate at a lower wattage, such as 450 watts, which corresponds to 50% of its power. This approach extends battery runtime during outages and reduces the need for maintenance and repairs.

Determining Your Requirements

To determine the maximum load capacity for your UPS system, check the wattage rating on the label of each device connected to the UPS. Sum up their wattage usage and add a 20% margin of error. This ensures that the UPS system operates at 80% of the calculated maximum load, providing a safety buffer for peak conditions or startup spikes.

Summary: Right Sizing the UPS System

For a 900-watt load, it is recommended to choose a 2 kVA UPS system to accommodate enough capacity. Operating at 50% of the load capacity allows room for potential maximum loads and prevents early stress on the system. Opting for a 1 kVA system with a 900-watt load means operating at 100% capacity from the start, which can strain the system and lead to premature failure.

UPS Runtime

Consider your battery runtime needs based on the location of the connected equipment. If devices are situated in a different floor or wing or at an offsite location, longer battery runtime may be necessary. Conversely, if your building has a generator that activates quickly during outages, a shorter battery runtime may suffice.

UPS Rating as a Guide

For example, a 1kVA UPS from N1 Critical Technologies provides 11 minutes of runtime at 100% load (900 watts). With a 900-watt load on a 2kVA UPS, you operate at 50% load, resulting in 24 minutes of runtime. Running 900 watts on a 3kVA UPS gives you over 30 minutes of runtime at a 33% load.

Advantages of Lithium-Ion UPS Systems

Lithium-ion UPS systems offer longer battery runtime compared to traditional lead-acid systems. These systems utilise lithium-ion battery packs that store more power in a smaller space, enabling extended runtime within the same size UPS unit. The additional minutes provided by lithium-ion batteries can be crucial during outages, making them the future of energy storage in UPS applications.

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