How to calculate the correct UPS power and correctly determine the power requirement
UPS sizing: How to choose the right power for your devices
Correctly sizing a UPS (uninterruptible power supply) is crucial to ensure a reliable power supply for your equipment. Both the connected devices and their power requirements play an important role here. In this article, you will learn how to determine power requirements, what conversions are required and how to adjust the UPS power to the needs of your applications. The backup time and sensitivity to voltage and current disturbances should also be taken into account when choosing the right UPS.
How high is the power requirement (electricity requirement) to be secured?
List all devices that are to be protected with a UPS. Don't forget to include screens, terminals, external data storage devices and other critical peripherals. Each of the systems to be protected has a nameplate with the connected load in volt-amperes (VA) (apparent power / (S)) or watts (W) (active power). Read off all VA values or watt values from the consumer devices to be protected (PC power supply, monitor, printer, etc.) and add them together.
Conversion:
| VA in Watt | VA * 0.65 = Watt | approximate value! |
| Watt in VA | Watt * 1.55 = VA | approximate value! |
| VA | Volt * Ampere = Voltampere V * A = VA |
Note: If, for example, you get 460 VA after adding all components, it is recommended to use a UPS of 750 VA or 1000 VA. A 500 VA UPS would probably be just about enough to bridge the devices in the event of a power failure in the initial phase, but since the batteries lose capacity as they age, a certain amount of oversizing is an advantage. Voltage peaks such as those that occur when devices are switched on should also be taken into account. And last but not least, the capacity should be sufficiently dimensioned for possible later system extensions.
Explanation: Apparent power / nominal power and active power
Apparent power (S) (nominal power) is the continuous power of the inverter integrated in a UPS and is given in volt-amperes (VA).
The actual active power (P) is determined together with the power factor cos φ according to the equation P = S * cos φ
What is the required bridging time?
Standard 5 – 10 minutes.
If longer backup times are required, the UPS must be dimensioned accordingly larger.
Example: For a PC with a TFT screen without additional peripherals, a 500VA UPS is sufficient. However, if a longer backup time is required, a 1500VA or 2000VA UPS can be used.
How sensitive is the respective application to voltage/current disturbances?
PCs are not too sensitive because the power supplies can compensate for small fluctuations. This means that a normal PC does not normally need an online UPS. A line interactive UPS offers the best protection in terms of price/performance ratio.