What are applications of uninterruptible power supplies

UPS - Uninterruptible Power Supply

Many devices and machines have to be available for almost 100% of their runtime. This includes servers and routers, e.g. B. keep the internet running. In addition to hardware and software problems, the power supply is also one of the Achilles' heel of every communication and information technology device. Therefore, important devices are equipped with a UPS, uninterruptible power supply. But not only a power failure, but also short-term undervoltage and overvoltages should be absorbed by the UPS.
Due to the different needs of the individual devices, three classes have established themselves in the UPS area, which the International Engineering Consortium (IEC) has defined under the product standard IEC 62040-3 and the European Union under EN 50091-3.

  • Standby or offline UPS
  • Line interactive, network interactive, delta conversion or single conversion UPS
  • Online double conversion or double conversion UPS

Standby or offline UPS

The simplest and cheapest UPSs (according to IEC 62040-3.2.20 of UPS class 3) are standby or offline UPSs. They only protect against power failures and short-term voltage fluctuations and peaks. Undervoltage and overvoltage are not compensated. Due to the switching time between mains operation and battery operation of 4 to 10 milliseconds (ms), interference voltages, voltage dips and voltage peaks are not detected below this time.
Offline UPSs automatically switch to battery operation in the event of overvoltage or undervoltage. Many UPSs then deliver a square-wave voltage at the output. Devices with inductive load, e.g. B. laser printers are unsuitable for these UPSs. Robust consumers such as small telecommunications systems and individual computers with peripherals that are equipped with primarily clocked power supply units with overvoltage protection and voltage filters are recommended and practical. The efficiency of the offline UPS is 95%.

Network interactive UPS

Network-interactive UPSs (according to IEC 62040-3.2.18 class 2) work in a similar way to standby UPSs. They protect against power failure and short-term voltage peaks and can regulate voltage fluctuations through filters. The switchover time from mains operation to battery operation takes 2 to 4 milliseconds (ms). Conversely, there is no delay in switching. Network-interactive UPSs usually deliver a stepped output signal. The efficiency is between 95 and 98%. This decreases when the output converter becomes active.
Line-interactive UPSs are suitable in areas where there are a lot of voltage fluctuations. Individual computers, larger telecommunications systems and networks can be protected. The protection of highly sensitive systems should be avoided.

Online UPS

The UPS technologies described so far all have one serious disadvantage: the load is only fed from the battery in the event of a power failure. However, the switchover time causes problems for highly sensitive systems.
The double-conversion or online UPSs (according to IEC 62040-3.2.16 class 1) are considered to be real power generators that constantly generate their own mains voltage. This means that connected consumers are permanently supplied with mains voltage without restrictions. The battery is charged at the same time. The input voltage can fluctuate between 160 and 290 V. The output voltage corresponds almost to a sine curve. But it has better properties than electricity from the socket. Without any interference voltages, electromagnetic influences, frequency interference and voltage distortions. If the UPS has galvanic isolation or an isolating transformer, even interference via the neutral or earth conductor is filtered out.
Continuous converter UPSs are equipped with a static bypass to which the loads are switched. Since the voltage is constantly being converted during operation, electrical losses and heat arise. The efficiency is therefore only 90%. The service life of the batteries is only 3 to 4 years due to the constant load.
Double conversion UPSs are used in highly sensitive areas in computer and communication technology. For this comprehensive protection, money must be invested accordingly.

Properties at a glance

UPS classclass 12nd gradeClass 3
powerfrom 500 VAup to 5 kVAup to 1 kVA
applicationServer and data communicationindividual computers, PBXs and networksSmall consumers, individual computers
protection againstComprehensive protection through constant generation of a sinusoidal voltagePower failure, filtering of voltage fluctuations and peaksPower failure, brief voltage fluctuations
Switching time2 to 4 ms4 to 10 ms

Purchase advice

Which UPS class?

Business-critical applications require double-conversion UPSs (class 1). Computers and servers get by with class 2 UPSs. Offline UPSs (class 3) are sufficient for cheap devices without expensive components.
Devices with uneven power consumption are generally unsuitable for UPSs.

Shutdown time

In the event of power outages or constant voltage fluctuations, all devices must be shut down properly to avoid hardware damage and data loss. The output of the UPS must be designed for a correspondingly long time.

Minimum performance

The decisive factor is the power consumption of the devices supplied by the UPS. This value is multiplied by 230 V and 30% added as a security. If the power consumption is unknown, then the real power is divided by 0.6. This gives approximately the apparent power in VA.
So that the UPS does not have to be upgraded with new acquisitions, we recommend planning a power reserve of 15 to 25%.


UPSs are available in a wide variety of designs. In addition to the normal floor-standing units, there are also rack modules for 19 ". It is important to choose the location beforehand and then determine the construction. Particularly large UPSs are difficult and difficult to install and maintain UPSs that are difficult to access are always a nuisance.

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