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Chapter 4:
UPS - Uninterruptible Power Supply


Regulating Your Computer's Power Supply

Every personal computer user needs to know that power surges, spikes, and overloads happen. Threats and risks that arise from the fact that computer hardware runs on electricity can be a matter to think about while implementing a security plan. The power and electricity department or personnel of an organization must ensure a smooth and constant supply of electricity.  If the supply of electricity to the hardware is interrupted unexpectedly or varied significantly, or brown-outs and black-outs occur, consequences could be serious.  Shutting off and on frequently because of a power loss can weaken the hard drive.

Below are some tips concerning your computer's supply of electricity: 

1.  Get an Uninterruptable Power Supply (UPS).

A UPS will tell you when the power drops or fails completely and will give you between five and 10 minutes to properly shut down your computer.  Desktop machines might be able to get away with a simple surge protector, but most machines should have better power conditioning, such as the UPS.  Make sure that the UPS or surge protector is designed to handle the amount of power that's being plugged into it.  UPS's are discussed at length in Section G below.

2.  Install an electrical line filter to filter voltage spikes.

3.  Use anti-static carpeting.

4.  Wear grounding wrist straps when opening up computers.

5.  Don't put computers on shelves or under heavy equipment.

Earthquakes and other sources of large vibrations happen.  Use rubber or foam mats under computers in areas with high vibration.

UPS - Uninterruptible Power Supply

In today's electrical system environments, power disruptions are very common. These disruptions can be due to various reasons like fault in the distribution system, operations of the nearby equipments, lightning strikes, normal utility operations, etc. In order to eliminate and reduce the loss of precious time and resources, it is necessary to provide a proper level of power supply and power protection. But there are some issues associated with power supply like the matters relating power smoothing, preventing sudden surges or drops in supply, and the supply itself. Blackouts and power dips can cause the computers to shut down suddenly, losing any unsaved data that is only stored in temporary memory or RAM. Sometimes sudden surges or drops in supply can also cause physical damage to computer components. An Uninterruptible Power Supply (UPS) can be an answer to this. These devices are designed to provide continuous power to a load, even with an interruption or loss of utility supply power. A UPS (uninterruptible power supply) is used to protect against sudden loss of power. It's somewhat of a misnomer, as it doesn't itself provide power - it is essentially a large battery that charges itself from the power main. The computers are plugged into the UPS, and if the mains power cuts out, the UPS provides enough power for the computers to shut themselves down and save all their information.

Common Power Problems

Below are some common power problems and their general power protection solutions.

Voltage Surges and Spikes

Surges: Sudden increases in electrical current through the line. Surges can be triggered by heavy equipment being turned off or by utility switching. Surges happen frequently but may not be noticed because they last such a short period of time. They can damage hardware and corrupt data. (Power protection solutions: UPS, surge suppressor or line conditioner)

Spikes: Increase in voltage through the line for a very short period of time. The results can damage hardware and data. (Power protection solutions: UPS, surge suppressor or line conditioner)

Brownout or Voltage Sags
A reduction in the incoming electrical current and the cause of most power problems. A computer has to work harder when it is not being supplied enough power creating more wear and shortening the life of critical components. (Power protection solutions: UPS or line conditioner)

Blackouts or Power Failure
Complete loss of power can cause the obvious problems of lost data and hardware damage. When power is restored one can also experience the power problems mentioned above: surges, spikes and voltage sags. (Power protection solutions: UPS)

Frequency Variations
Change in frequency stability. (Power protection solutions: UPS, surge suppressor or line conditioner).

Line Noise
Signals that are embedded or overlaid onto incoming power. This usually doesn't damage hardware but can corrupt data. It is caused from the use of other electrical equipment or household appliances like microwaves, hairdryers or vacuum cleaners. (Power protection solutions: UPS, surge suppressor or line conditioner).

To determine the requirements for a UPS generally involves a balance of cost vs. need. The components of a basic UPS system contain a battery charger/rectifier, batteries, and an inverter. The battery charger is a rectifier that converts AC power to DC in order to charge the batteries. The batteries store power that is supplied to the load when there is a loss or decrease of a certain tolerance of utility supply power. The inverter converts the DC power from the battery to AC power used to supply the load.

Types of UPS

Offline UPS or Standby Power Supply

An offline UPS provides battery power to equipment when the mains power supply falls below a pre-determined limit (usually around 200 V AC). This battery usually lasts ten minutes. Offline UPS units are often referred to as standby systems, as the inverter is in standby mode until the mains power supply fails. They are inexpensive and recommended for home offices. Offline technology should be avoided for applications where there is frequent power disturbance.

Under normal operating conditions, AC power from the utility passes straight through the UPS to the critical load. A charger converts AC power to DC to charge the battery. The inverter is used to convert the DC power from the battery to create AC power to support the load when the utility fails. Normally the inverter is operating in the standby mode, keeping the batteries charged. Should the utility power go out of specification, the inverter powers the load, drawing energy from the battery. This topology is also called "single-conversion" because at any point of time, power is only being converted once (AC to DC or DC to AC).

Line-Interactive UPS

A line interactive UPS contains a regulator that boosts the mains power supply when it falls. It can regulate power to an acceptable level, without the use of a battery, during a brownout or surge in supply voltage. Similar to an offline UPS, there is a short period (i.e. transfer time) when a line interactive UPS switchs to battery mode during a blackout. Most line interactive UPS units have additional features including sinewave output, enhanced software and connectivity options. They provide a high level of protection, at an affordable price, for corporate applications.


This category resembles the offline product, but inserts a transformer or inductor in series between the utility power source and the load. This in-line inductor enables the UPS inverter to interact with incoming power and provide a measure of power conditioning to the load. This buck-and-boost circuitry helps in high and low input voltage conditions.

Double-Conversion On-line UPS

True on-line UPS units provide the highest level of protection. An on-line UPS absorbs the incoming AC supply, converts it to DC then inverts it to AC to supply critical power loads. An inverter supplies regulated AC power to loads at all times; either from rectified mains or a battery with an on-line UPS. In the event of a blackout, there is no transfer time or break in power supply.


Most on-line UPS units contain an automatic bypass to ensure continuous power supply during a short-term overload or UPS failure. They are ideal for critical loads, sensitive equipment such as medical or scientific technology and industrial loads. All on-line UPS units are fully generator compatible. These UPS units are often referred to as double conversions because they can convert from AC-DC to DC-AC.

Comparison of Prominent UPS Topologies

UPS Selection Criteria

After determining the specific UPS features required for the application and developing a list of qualifying UPS systems, selection principally becomes an issue of engineering quality, layout and economics. Below are some of the main criterions for selecting an appropriate UPS.

Output Power

It is necessary to consider the size of the load that is to be connected to the UPS. The load may consist of a specific type of computer, workstation, mini-mainframe, hard disk drive, or test equipment. Once the equipment requiring a continuous power source is identified, the necessary rating of the UPS system can be determined by adding the volt-ampere (VA) rating on the nameplate of the equipment to be served by the UPS.

Batteries Life
It should be mentioned that battery life is a major consideration for UPSs. Battery manufacturers' state a five-to seven-year life for the lead-acid batteries used in the UPS. However, the actual battery life is determined by how often the battery is called upon to take over when there is an outage, surge, sag or swell. Each time the battery takes over, its useful life diminishes.

If one is buying a more expensive unit, get the one with the software that automatically saves data, closes applications, and turns off the computer equipment in advance, before the UPS standby power goes out, following the mains failure.

Vendor Warranty and Onsite Service Options
Remember that batteries have a limited life-span and in two to three years time one has to replace storage batteries. Battery replacement is quite expensive in comparison to the initial UPS cost. Make sure to explore all the possible warranty alternatives with the vendor, so that one receives the option that is most convenient.

Additional Features
There are UPSs in the market with modem surge protection, electromagnetic interference (EMI) and radio frequency interference (RFI) noise filters. Consider them if these specifications and protections are of major concern for the sensitive electronic equipment proposed to be supported. Always exercise this option to best suit the customer needs, checking the vendor's capability to provide service for these value-adds.

UPS Buying Tips


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