Uninterruptible power supply

SFC Energy is a leading supplier of direct methanol– and hydrogen fuel cells. We also manufacture hybrid energy solutions for residential and industrial applications. Our fuel cell technology can be used for uninterruptible power supply.

What is meant by an uninterruptible power supply

An uninterruptible power supply (UPS) supplies power to electrical equipment in the event of a power supply failure. How does an uninterruptible power supply work? What are the different classes of Uninterruptible Power Supplies? Which uninterruptible power supplies does SFC offer?

All this and more is revealed in the following article.

Uninterruptible Power Supply Explanation

An uninterruptible power supply is a device that supplies power to an electronic device when the primary power source fails. Failures can occur, for example, in the form of short-term outages and fluctuations. UPS systems also provide protection against overvoltage and undervoltage.[1] For this purpose, the UPS is connected between the power supply lines of the respective devices or systems.

Uninterruptible power supply – when and why is it used?

In contrast to emergency power generators, uninterruptible power supplies are normally only used for short periods of time. Uninterruptible power supplies are used wherever power disturbances can lead to life-threatening, critical conditions. Typical applications of uninterruptible power supplies are therefore computers in data centers and hospitals, as well as in public authorities and other security-relevant areas. Nowadays, however, UPS power supplies are increasingly found in small and medium-sized businesses, as well as in private households. The reason for the increasing spread is the growing need to continuously supply communication and IT equipment with power.[2] Uninterruptible power supplies are often used to prevent data loss in the event of a power failure. Uninterruptible power supplies maintain the operation of the respective computer systems long enough to store important data and shut down the systems.[3]

Structure of an uninterruptible power supply

How is an uninterruptible power supply constructed?

The most commonly found are battery-based UPSs. Thus, most uninterruptible power supplies have an accumulator that is charged by mains power. The battery power of a UPS is usually at least 300 VA (volt amperes), but can increase up to several hundred VA. In this case, the power depends mainly on the load capacity of the power converters. The capacity of the batteries determines the maximum bridging time, which can range from a few seconds to several hours, depending on the need and purpose. If the demand for power and bridging time is very high, power generating sets are used to recharge the accumulators.[3]

Charging is performed via a so-called rectifier on the input side of the system. This converts the alternating current from the power grid into direct current. If the regular power supply fails, the battery takes over the energy supply. The inverter on the output side then converts the direct current from the battery back into alternating current.[3]

The type of battery depends on the size and capacity of the UPS system. For example, compact uninterruptible power supplies used in private households or smaller offices usually have small lead-acid, nickel-metal hydride or lithium-ion batteries. Large UPS systems, such as those used in hospitals, use far more lead-acid batteries, often as many as several hundred.[3]

Different classes of uninterruptible power supplies

What are the different levels of uninterruptible power supplies?

Uninterruptible power supplies are based on different technologies and can be divided into different classes accordingly. Which class is the right one for the application depends on the respective protection requirement. The following protection classes for uninterruptible power supplies are offered:

  • Class 1: Online UPSs
  • Class 2: Line-interactive or mains-interactive UPSs
  • Class 3: Offline UPSs

Online or double-conversion systems (class 1) are particularly suitable for backing up business-critical applications. Although uninterruptible power supplies of this type are somewhat more expensive than the other two technologies, they do not require any switchover times in the event of a power failure. Online UPSs therefore supply the connected devices with AC voltage without interruption and thus compensate for power failures, under- and overvoltages, frequency fluctuations or noise influences. The double conversion method is used here. The mains voltage is continuously converted into DC voltage and then flows through an inverter via the battery. In this way, AC voltage is constantly generated and then supplies the consumer devices. The current therefore flows permanently through the uninterruptible power supply. The only disadvantage: Due to the continuous operation, the devices have a comparatively short service life and a rather low efficiency of 90 percent at most.

The low-cost offline or standby systems (class 3) are mainly suitable for individual computers. The reason: They only protect against complete power failures and short voltage fluctuations. If the voltage drops to a certain value, the systems switch to battery operation. This step can involve delays of up to ten milliseconds – which the connected devices have to cope with without any loss of function. Since the devices are not in continuous operation, but only charge the battery during normal operation, they score with a long service life and a high efficiency of up to 95 percent.

Grid-interactive uninterruptible power supplies (Class 2) are based on a hybrid technology. They are more powerful or offer more protection than offline systems, but less than online UPSs. They are therefore less suitable for sensitive consumers and for regions with frequent voltage fluctuations. The systems supply the connected devices with mains voltage and can compensate for voltage peaks and drops. Compared to offline systems, grid-interactive UPSs have response times that are two to four milliseconds shorter. Their efficiency is 95 to 98 percent, making their energy consumption comparatively low.[4]

Recommended minimum power of an uninterruptible power supply

What minimum power should an uninterruptible power supply have?

In addition to the bridging time, the minimum power is an important consideration when selecting the appropriate uninterruptible power supply. What power a UPS should have depends on its intended use. After all, the system must be able to bridge power disturbances until the emergency generator takes over.
The required minimum power can be calculated from the volt and ampere values of the device to be protected. Usually, the values can be read from the nameplate of the device. Multiplying the volts and amps together gives the "apparent power" of the equipment in units of volt-amperes (VA). To determine the minimum power of the UPS, add the calculated volt-ampere values of all the devices to be protected. So when buying an uninterruptible power supply, make sure that its power does not fall below this value.[5]

Power supply UPS with SFC Energy

UPS system manufacturer SFC produces hydrogen and direct methanol fuel cells that serve as power generators for numerous mobile and stationary applications. The energy solutions are equipped with different outputs depending on the intended use and reliably generate UPS power – for temporary applications as well as for continuous operation.

You want to buy a UPS system? SFC Energy offers a variety of fuel cells for different usage requirements. While the EFOY models are best suited for temporary use, low power requirements, or solar-powered installations, the EFOY Pro models are used for completely self-sufficient applications, higher power requirements, and continuous operation. EFOY Pro, for example, is also used to compensate for low solar power. Both series can be used in hybrid operation.

The EFOY Hydrogen Fuel Cell complements the SFC product portfolio with a high-performance energy solution. The EFOY Hydrogen Fuel Cell is also used for back-up power supply – and is able to ensure power supply in case of a grid failure. Typical areas of application are critical infrastructures or emergency power supply in the field of mobile communications or smart traffic.[6]


Whether damaged hardware or destroyed data files – uninterruptible power supplies protect against the consequences of power disturbances and failures. Only a UPS selected according to the user’s needs offers the necessary protection. Whether it should be an online, offline or hybrid variant depends on the respective area of application and the devices to be protected. While offline systems have switchover times of up to ten milliseconds and are particularly suitable for small consumers, online UPSs impress with their immediate switchover from mains to battery operation and their suitability for particularly sensitive devices. Hybrid systems achieve switchover times of two to four milliseconds and can be used for individual PCs and communication devices. The purchase of an uninterruptible power supply should therefore be well considered and aligned with the respective application requirements.