+351 289 860 320 (*) geral@tecnicontrol.pt


UPS Concepts

UPS – Uninterruptible Power Supply

Electronic systems such as computer networks, management systems and security systems are essential tools to ensure business continuity and make your organization run smoothly and effectively.

In fact, we depend on stable and reliable electric power supply to live our lives; however, unfortunately, power supplies worldwide are unreliable. According to an IBM study, computers are subject to an average of 128 power disturbances a month. This means that computer systems and their files and applications, such as email, financial information, working documents, photos, music and all kind of records are at risk more than four times a day!

While there are many less-expensive methods you can employ to provide some degree of protection from power problems, none of them can insulate your system from power troubles as well as a good uninterruptible power supply (UPS).

The idea behind a UPS is pretty obvious from the name; in addition to filtering, enhancing or modifying the utility power, special circuitry and batteries are used to prevent equipments from losing power during a disruption (blackout) or voltage sag (brownout). These units are called different names depending on their typology design, but all fit into the general category of “backup power”.

Without adequate power protection from a UPS, most organizations are faced with stops, resulting in loss of information, productivity and profit. The easiest way to safeguard their systems and mission-critical objectives is to invest in UPS power protection.

An Uninterruptible Power Supply (UPS), also known as a battery back-up, provides emergency power and, depending on the typology, line regulation as well, to connected equipment by supplying power from a separate source when utility power is not available.

A generator can not substitute a UPS because, in the event of a disturbance in the power supply, there will always be a gap between the power supply failure and the generator firing from the “standby” state. This disruption in power supply could result in significant financial losses and justifies the need for a UPS.

A UPS differs from an auxiliary or emergency power system or standby generator, which does not provide instant protection from a momentary power interruption, as a UPS can be used to provide uninterrupted power to equipment, typically for 5–15 minutes until an auxiliary power supply can be turned on, utility power restored, or equipment safely shut down.

While not limited to safeguarding any particular type of equipment, a UPS is typically used to protect computers, data centers, telecommunication equipment, surgical operating rooms or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss.

A UPS not only provide protection against all types of power supply failure, but also are able to filter a wide range of issues encountered in the electric power supply, thus providing more sensitive loads with a clean power supply.

In short, the uninterruptible power systems perform two functions:

  • Filter disruption of the supply network
  • Provide power to the loads in case of mains failure

Once considered an expensive luxury, UPS are now available quite inexpensively. While once it would be recommended a UPS to only those whose systems really needed them, now we can say that anyone who uses critical equipment for any work purpose should be thinking seriously about getting one.

If one considers his time valuable, a UPS can pay for itself the first time the power flickers or goes out.

UPS units range in size from units to back up single computers without monitor (around 200 VA) to units powering entire data centers, buildings, or even small cities (several megawatts).

Impact of problems with electric power feeding:

Disturbances in the power supply can affect the performance of electronic devices, so it’s important that the electricity supply is stable and clean.

UPS units are used to correct various common power problems, such as:

  • Power failure
  • Voltage sag
  • Voltage spike
  • Under-voltage (brownout)
  • Over-voltage
  • Line noise
  • Frequency variation
  • Switching transient
  • Harmonic distortion

Electrical noise, except in the worst cases, it’s generally an event “not visible” but results in the greatest threat to the ability to operate electronic equipment and contributes to the wear of electronic components.

Problems in supply can cause:

  • Equipment lockout, programs failure and systems failures
  • Data corruption
  • Errors in data processing
  • Errors in data transmission
  • Printing errors, hardware damage

The feeding problems may be transmitted by one or more sources:

  • By your own internal electric network
  • By the electric power provider feeding
  • By the building electric distribution network itself
  • By other equipment in the building
  • By the weather, for ex. Thunderstorms

UPS’s Technologies

The general categories of modern UPS systems are on-line, line-interactive or off-line.

How does a UPS works?

A UPS is an item of electrical equipment that is positioned between the input power supply and selected items of electronic equipment, referred to as “load”.

It has a battery to provide power in case of power cut. The length of time that a load can be supported ~ (autonomy) depends on the size of the UPS’s battery.

When power fails, the UPS’s batteries ensure a clean and unbroken supply, available to keep the load fully operational.

It provides time to shut down key information systems in a safe and orderly manner preventing data loss/corruption.

It also protects computers and data from a variety of problems related to energy.

A UPS is a tool to ensure business continuity.

Continuous service

Continuity of service is the goal and to achieve this, a UPS usually comes with a set of features and capabilities that can create a communications interface between the UPS and the load and, in addition, allowing the user to monitor the performance of the UPS and batteries.

Easy to use software means one can customize the UPS to meet the specific needs, including procedures to set automatic load shutdown.


Conversion and Inversion Circuitry

All UPS include core circuitry that manipulates electricity, converting it from the AC power supplied by your utility company to DC power stored in the batteries, and back again for use by your equipment. The exact type, nature, size and quality of this circuitry depend on the type of UPS, and more specifically the make and model you have chosen. As with all things, the better the unit, the higher the quality of the components. And as with all things, quality is often correlated to price.

Most modern UPS are microprocessor controlled. There is actually a small computer embedded within the UPS itself that controls the key functions of the UPS.

This includes detecting AC power failures, handling switching between power sources, monitoring the status of the battery, controlling the status indicators and so on.

If something happens that you think that can be a failure, including lack of autonomy by aging or defective batteries, contact your dealer or a brand’s Authorized Service Center for the UPS to be examined and/or its components replaced by qualified personnel to avoid damage.


Other than the core circuitry of the UPS, the other main component is the batteries, which of course holds the energy that is used by the UPS to run your equipment. It is the size and number of the batteries more than anything else that dictates the size of the UPS unit as a whole. The size of the batteries is also proportional to the amount of energy that is stored in the UPS, and therefore, the length of time that the UPS will run for a given load.

All batteries are rated in terms of their nominal voltage (in Volts), and their capacity (in Amp-hours or “Ah”).

1 Amp-hour represents energy sufficient to provide 1A of current for one hour at the rated voltage. So, for example, in theory, a 17 Ah/12V battery can run a 17A/12V load for one hour or a 1A/12V load for 17 hours.

In practice, the capacity of the battery depends on how fast you are drawing current from it, so saying a battery has a particular Ah capacity implies measuring it at a particular discharge rate.

The larger the Ah rating, the more capacity the battery has – Most UPS brochures don’t discuss the Ah capacity of the batteries directly, or its number, so you may have to look at a specification sheet to get the details as this has an important influence on the run time of a UPS.

Some UPS have expandable battery packs, helpful if you add loads to your system. You can add additional UPS autonomy adding a battery pack available from the manufacturer or authorized dealer.

Since they are based on a chemical reaction, all batteries fail eventually. Many better UPS will detect this condition by examining the voltage of the batteries as they are charging. Others may detect it during a self-test.

Over time, the battery will degrade, and its capacity will diminish, leaving it less able to provide protection for your equipment.

Battery life depends basically on the amount of charge/discharge cycles, which should be as less as possible, and of the working environment temperature.

Generally, a UPS will not discharge its batteries 100%, because taking a battery down to the fully-discharged state dramatically reduces its life.

Replacement batteries are available from the UPS’s manufacturer or authorized dealer.

Status Indicators

Most UPS come with a variety of indicators to tell you the current status of the UPS. These normally come in two basic categories:

  • Visual indicators, that can be LED or LCD displays, are used to indicate the general status of the UPS as well as problem conditions.
  • Audible indicators, sometimes called alarms, are used to draw attention to problem situations specifically.

The exact number and type of indicators varies from model to model, with more expensive units generally having more of each type. As always, check your user manual for details.

In addition to these simple status indicators, better models come with special software for controlling and monitoring the UPS, which can be very powerful on larger ones.


Control and Monitoring Software and Hardware

One of the most useful “special features” of newer UPS models is control and monitoring software, which gives you, extended status information and control over the operation of the UPS unit.

Nowadays, even lower-end UPS have some control and monitoring capabilities (though the hardware and software required may be an add-on option). As UPS power increases, there are more parameters to control and, therefore, its software is more complete.

The hardware part of the equation normally takes the form of a special cable that runs from a special interface port on the back of the UPS to an interface port on the PC; traditionally a serial port was used for this function, but some newer units can also interface using an USB (universal serial bus) port, or even directly over an ethernet network port.

The software used for controlling the UPS varies by manufacturer and model, but generally includes functions in the following general categories:

  • Status: The software will show various details about the UPS’s current status, such as its load, the batteries’ state of charge, the UPS’s environmental condition (temperature, humidity, etc.) and the electrical characteristics of its input and output power.
  • Logging: The software will keep track of various events that occur, such as self-tests, power interruptions and the like. This is useful for seeing locally or remotely how often and for how long the power was interrupted.
  • Diagnostics: The control program will let you perform various tests on the UPS, or let you set up a testing schedule.
  • PC Alarms: The software can be configured to send notifications to the PC to which it is connected, or to another PC on a network, when the UPS encounters a problem condition or switches to battery operation.
  • Automatic Shutdown: Probably one of the most important and useful features of this sort of software (read more…).


Most UPS have a self-test function built into them, what commands the UPS to do a self-test when it first turns on. The purpose of the self-test is to ensure that the UPS is functioning properly.

Periodically, through a predefined schedule (ex.: once a week or once a month), can be defined self-tests to the batteries’ condition.

During the battery self-test you may notice some of the UPS’s indicators flash, and the unit may emit audible tones, but there should be no noticeable effect on your protected loads.

If you are running UPS control software you may be able to control how often your unit does a battery self-test and you can also usually tell the UPS to do a self-test on demand; you may need to do this if the batteries fails a self-test on start-up due to being discharge from use.

Of course, the battery self-test is an important feature, but it does not take the place of a real-world test: This means simply firing up the UPS and whatever loads it’s supposed to run, and then pulling the UPS plug and see how well it works.

You don’t want to do this too frequently however, as it will run down the batteries and over time, too many charge/discharge cycles will reduce battery life; however, you should do it periodically, especially if you change the composition of your protected loads.

Parallel Applications: Redundancy + Power Parallel

Parallel redundancy in N+1 mode:

In large business environments where reliability is of great importance, a single huge UPS can also be a single point of failure that can disrupt many other systems.

To provide greater reliability, multiple UPS (or power modules in a UPS) and batteries can be integrated together to provide redundant power protection equivalent to one large UPS.

“N+1” means that if the load can be supplied by N modules, the installation will contain N+1 modules – In this way, failure of one module will not impact system operation.

Multiple redundancy mode:

Many equipments offer the option of redundant power supplies, so that in the event of one power supply failing, one or more other power supplies are able to power the load. This is a critical point – each power supply must be able to power the entire equipment by itself.

Redundancy is further enhanced by plugging each power supply into a circuit (to a different circuit breaker/phase).

While it is common practice by uninformed people to plug each of these individual power supplies into one single UPS, redundant protection can be extended further yet by connecting each power supply to its own UPS – This provides double protection from both a power supply failure and a UPS failure, so that continued operation is assured. This configuration is also referred to as 2N redundancy.

If the budget does not allow for two identical UPS units then it is common practice to plug one power supply into mains power and the other into the UPS.

Parallel Redundant mode:

In critical business environments where reliability is of great importance, a single UPS is a “one global point of failure” issue.

To provide greater reliability, two UPS modules and batteries can be integrated together to provide redundant power protection equivalent to one UPS of the same power.

“Parallel redundant” means that the load is being supplied by two UPS modules – in this way, failure of one module will not impact system operation as the other is able to supply power to the load without disruption or disturbance.

Parallel Power mode:

In business environments where load simultaneity is always varying is of great importance to have an UPS system that can grow as your power needs grow.

To provide greater flexibility, two or more UPS modules and batteries should be able to be integrated together to provide added power protection equivalent to one UPS of the same power.

“Parallel Power” means that the load is being supplied by two or more UPS modules – In this way, simply adding more modules to the UPS system, power can be increased to supply the load without the need of new and separate electric circuit networks, disruption or disturbance.