Category: Archive Informatics

How does it work

An uninterruptible power supply is a particular device that guarantees power supply even in the event of an electricity blackout. Sometimes the uninterruptible power supply is also known by the acronym UPS, which stands for Uninterruptible Power Supply (or Source ). The difference between an uninterruptible power supply and a common emergency power system (or a generator) is represented by the fact that the UPS is able to supply current instantaneously (or almost). This effective "protection" from electrical interruptions is guaranteed by the presence of one or more batteries associated with an electronic circuit. Most uninterruptible power supplies are capable of providing energy for periods of time that typically range from 5 to 15 minutes; this especially applies to smaller models (around 200 VA). Obviously this is not a lot of time available, but being able to rely on electricity even for a few minutes allows for example to restore the power, use a generator or – in the worst case scenario – be able to save any data and safely turn off the connected device. This aspect is particularly important, for example, for computers. Uninterruptible power supplies can be connected to any type of instrumentation or electronic device. Not only computers, therefore, but for example also data processing centers, telecommunications equipment, and all other cases in which the sudden lack of power can cause loss of information, damage to the system, interruptions of service or, in the worst cases , injury or death of people (e.g. hospital equipment). This is why there are uninterruptible power supplies of very different sizes: they range from small-sized units (for example for the protection of a computer) to large devices designed for computer processing centers, entire buildings or even residential areas. Uninterruptible power supplies are useful not only when the power goes out, but also in cases where electricity is supplied inconsistently, with peaks and voltage swings.


There are uninterruptible power supplies on the market from different manufacturers, models and powers, but essentially all of them are based on three fundamental elements represented by:

  • an AC/DC converter that allows you to transform alternating voltage into direct voltage;
  • one or more rechargeable batteries which inside them store the electrical energy coming from the converter into chemical energy;
  • a DC/AC converter which transforms direct voltage back into alternating voltage which can be used by common electronic devices.

In addition to the one listed above, the UPS also includes an AVR, which is an element that serves to dampen voltage peaks by regulating the incoming current to the connected device. The battery, as understandable, represents the central element of the UPS and is usually lead acid. Its power must be sufficient to power the connected devices, and in the case of multiple batteries, these are connected in parallel to allow better operation of the UPS.

Main typologies

Depending on their technical characteristics, there are different uninterruptible power supplies. Off-line uninterruptible power supplies are the cheapest and make up the majority of devices used at home. The input current passes from the UPS to the connected devices and in the meantime, thanks to the power supply, the connected batteries are kept charged. Following a power failure, the response time is a few milliseconds (typically, no more than 5 or 6). This technology is also called "standby" and is ideal for low-power loads such as single peripherals. In line-interactive UPS only part of the current entering the device is filtered, but in the event of a blackout the intervention times are very short, shorter than with offline UPSs. These devices allow the output voltage to be stabilized and, at the same time, to recharge the battery. Line-interactive UPSs are recommended, for example, for users who often experience power fluctuations but only rarely experience blackouts. Online UPSs are directly connected to previously charged batteries, therefore in the event of a sudden power failure they come into operation immediately. This happens because all the incoming current is filtered by the UPS and part of it is diverted to charging the batteries, while part is destined to power the connected devices. These UPS guarantee the best performance ever, but they are also quite expensive.

Which one to buy

Uninterruptible power supplies are not yet very widespread devices. In addition to industrial uses, in most cases the average user is represented by a computer user who wishes to prevent any problems due to a possible power failure. Regarding the choice of an uninterruptible power supply, the first thing to evaluate is undoubtedly the power. Obviously it is necessary to choose a model whose power is indicated for the needs of the connected electronic equipment. Power is indicated with the unit of measurement VA ( Volt-Ampere ) which from a quantitative point of view is equivalent to the Watt. But how to calculate how much energy a device needs? For example, the eXtreme Power Supply Calculator program is very useful and can be downloaded for free in its basic version. For greater safety, once the power absorbed by the device or devices has been identified, it is recommended to double the value (or even triple it, just to be safe) and choose accordingly. Usually an uninterruptible power supply of 300-400 VA is sufficient for a computer, although from a precautionary point of view it is advisable to have one of at least 500 or 600 VA. The uninterruptible power supplies that can be found at low prices, for example in the stores of large IT chains and in supermarkets, are not the most reliable. Better to spend a little more and choose specialized brands that can guarantee effective protection such as, for example, APC, Daker or Atlantis Land. The best uninterruptible power supplies are those that can be connected to the computer via a USB socket, and which are therefore controlled thanks to special software. In this way, for example, it is possible to set the automatic saving of data and the safe shutdown of the computer a few minutes after the UPS comes into operation. By doing so, you avoid the "traumatic" shutdown of the computer at any moment and the loss of data.

Connections and maintenance

The UPS can be connected directly to the computer or other devices without necessarily having to install the management software. If you want to program the device, simply install the CD with the software contained in the package. The connection of the UPS to the computer can typically be made via a USB port, a serial connection or with an Ethernet cable. Due to continuous use, after some time it is necessary to replace the battery of the UPS. It is usually advisable not to wait more than three years to carry out this replacement: using batteries that no longer hold a charge can in fact lead to very dangerous sudden shutdowns. To replace the battery, it is best to consult the manual and, if necessary, contact an expert in electronic products.

Published: 2011-12-19From: Redazione

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