In this post you will learn how to select the UPS that best suits your needs based on the equipment you need to protect, its consumption and the required autonomy time.


UPSs are rated based on Apparent Power ‘S’ that can be measured in Volt Amps (VA). This magnitude is related to the real power ‘P’, measured in watts (W), by means of the Power factor (FA, pdf or cosine of φ).In case you know the consumption of some of your devices in volts (VA), you just have to add them all up. If, on the other hand, you know the consumption of other devices in watts (W), you must divide the total value by the Power factor:

VA = W / FA

The Power Factor is set by the UPS and varies depending on the typology, range and model of the UPS. The higher this value is, the more efficient the UPS is, the more real power (W) it offers to protect equipment and the less energy it will consume when supplying it. For example, a basic UPS with a capacity of 1000VA can offer 600W real, while a more efficient one can offer 900W real with the same 1000VA. The basic UPSs have a Power Factor of 0.6 and the professionals around 0.8 – 0.9.


A correctly dimensioned UPS provides 5 to 10 minutes of autonomy, although it always depends on the load it has connected.Choose a larger UPS model that will generally mount more or more capacity batteries. Purchase battery modules compatible with the UPS. This option is usually only available in professional in-line UPS and on-line UPS from 3KVA. Acquire an Emergency Power System that allows you to externally connect the batteries you need to achieve the desired autonomy.


NAS servers have a low power consumption compared to a PC but, on the other hand, they are more delicate when it comes to shutdown and need a longer autonomy time, especially if they are configured in RAID. A 600VA – 650VA UPS that mounts a 12V and 7Ah battery may be sufficient for NAS equipment with one to 4 bays and an 800VA – 850VA model that mounts a 12V and 9Ah battery for more powerful models.


Electric motors, pumps and boilers that mount any of these components require a UPS with a pure sine output to function properly. In case the peak consumption of these loads does not exceed 2000VA, there are sinusoidal on-line UPSs ideal for these applications for a reasonable price. Above this power or for long autonomy times, it is necessary to go to online models that, apart from being able to handle more load, mount more batteries.

Another important concept for sizing a UPS to protect electric motors and pumps is the peak power they demand at startup. Normally, these equipments need a power higher than the nominal power (the one they consume when they stabilize) when they start working. This peak power is usually around 3-5 times the nominal power and it is important that the UPS be able to manage it, even if it occurs only a few times. You can check the power in the equipment manual or on the electrical specifications label.


Because a UPS integrates components and electronics that handle moderate or high powers, it must be able to cool down and to do so, it mounts one or more fans depending on the model. These fans will generally rotate at different speeds depending on various conditions:

  • UPS load level.
  • If you have activated the AVR stabilizer in the case of online UPS.
  • If it is in battery mode.
  • If you are charging the batteries.

Generally, online UPSs need more cooling because they are continuously generating the signal, while online UPSs need to ventilate with more power during power outages. Therefore, in-line UPSs are better suited to be placed next to work stations. In the event that it is required to protect equipment inside a recording studio or high consumption equipment next to workstations, it is recommended to install a professional in-line UPS. These models are manufactured with better quality components and processes that make them more efficient and quieter.