by November 1, 2004 0 comments

Unlike most IT equipment where you have a host of technologies and features to choose from, a UPS is a relatively simpler animal. Nevertheless it can be quite a tough task deciding which one to buy. After all, it’s the UPS that provides power to your computers and other peripherals when there’s a power cut. If it fails, all your systems come down. So the choice of UPS depends upon how critical the IT systems for your business are, and how much uptime you need for them. For example, if your business involves directly dealing with customers, as in a retail chain or hotel, then you can’t afford to have systems going down when customers are waiting at the counter. So provide separate UPSs for each computer with longer backups, and then even have a generator for additional backup. In a small office, on the other hand, where customers aren’t standing on your head, then such high up time may not be required. So choose a UPS with lesser backup, just sufficient to save all your work and shut down systems. You may want to provide generator backup if the power cuts last too long. If you have a server room, then you might require longer backups for the servers, as they need to be up 24×7. As you can imagine by now, the type of UPS and associated power-conditioning equipment changes with the requirement, and so does the cost. Let’s look at a few simple things to keep in mind when choosing a UPS for your business. 

As you do before buying anything else, do some homework before buying a UPS. Start by analyzing the power situation in your area. This includes simple things like determining how frequent and how long are the power cuts in your area, and the level of voltage you get. Do you frequently face low voltage situations, also called brownouts? Or perhaps the voltage is very high. If you’re in an industrial area with heavy machinery, then you might even get a lot of other disturbances in your utility power, like power surges, harmonics, etc. You can easily figure out some of these things, like power cuts, while for others, you may need an electrician or ask the UPS vendor for help. 

Next figure out how many systems you need to provide backup for, and how much power they consume. This will help you determine how large a UPS to buy. 

Always choose a power rating that’s at least 15 percent higher than the power consumed by your existing load. It’s always good to have this much buffer. One thing to beware of here is overrated UPSs. Many vendors, in order to cut costs, would overrate their UPSs, while the actual load handling capability of their UPS would be much lower. That’s why you need to first determine how much power is actually consumed by your computers and then check whether the UPS can handle that much load.

Next, determine whether to go for centralized or distributed backup. In the retail or hotel example we gave, not too many computers are used, so you’ll need to buy multiple smaller UPS units. One UPS could be for computers at every counter, one to backup the servers at the back end, etc. In other words, distributed backup is useful in places where computers are spread out. Conversely, if your organization has all the computers in one place as in a government office, a centralized backup is a better option in terms of its cost effectiveness and ease of maintenance. Here again, you should have at least 50 to 100 computers in the office to merit deploying centralized backup, else distributed backup suffices. You may also need extra power for critical elements such as servers, networking devices, and even non-IT equipment like local PBX etc that are all critical to your business. For these, go for additional smaller UPS units.


American Power Conversion 
Datex Electronics
DB Power Electronics
Emerson Network Power
Hita Technologies
KLA Electronics
Microtek International
Numeric Power Systems
Powerware International
SuKam Communications
TVS Electronics
WeP Peripherals

Wide cost differential between different technologies accounts for the importance of choosing the right UPS technology. So is the level of protection offered. 

You might be familiar with terms like offline, line-interactive and online UPS systems. An offline UPS is the simplest of all. When a power cut occurs, an offline system will switch to battery. Due to this switching behavior, there’s some delay before the PC starts getting its power from the batteries. This must be minimal in order to prevent your PC from rebooting. Offline UPSs provide square wave output from the batteries. Due to their simpler design, these are the easiest to manufacture and therefore the cheapest. Nowadays, there are many manufacturers that also provide automatic voltage regulation in their offline UPS designs. Line-interactive UPSs, on the other hand, continuously monitor the incoming line voltage and provide a stable output. If there’s a dip or rise in the mains voltage, this type of UPS will kick in the step-up or step-down transformer to increase or decrease the output voltage to the load. They also provide a better waveform to the computer load. Online UPSs are the most complex of all, providing the maximum power protection and also being the most expensive. They always supply power through the batteries. So when there’s a power cut, no switchover occurs, unlike in the other two technologies. It also gives a constant output voltage that will not dip or rise due to this. Their models mostly start at 1

Heat is the main age to the load. They also provide a better waveform to the computer load. Online UPSs are the most complex of all, providing the maximum power protection and also being the most expensive. They always supply power through the batteries. So when there’s a power cut, no switchover occurs, unlike in the other two technologies. It also gives a constant output voltage that will not dip or rise due to this. Their modelnemy of both computers and the UPSs. If your computers get overheated, they may hang or give poor performance. Overheating also reduces battery life in UPSs. So ensure proper ventilation for the area where your computer is kept, and also maintain the temperature level by providing proper air-conditioning. 

Know your power problems

There are more power problems than mere power cuts, over and under-voltaging. Let’s take a look at these. 

Power Surge: This is the sudden increase in the main voltage, which occurs when heavy motors and machinery are switched off. Since these draw a lot of power, when they’re turned off, the voltage rises suddenly. A power surge usually lasts for 1/20th of a second. 

Spike: Similar to a surge, except that spikes are the result of lightening strikes or when utility power comes back after a failure.

Sag/Brownout: A dip in the mains voltage. If the dip lasts for less than a second, it’s called a sag, else a brownout. While surges occur when heavy machinery is turned off, brownouts occur when it’s turned on. 

Frequency Variation: The mains frequency is fixed at a value, which is different for different countries. In India, this is 50 Hz. Any variation from this frequency can damage electrical and electronic equipment. Therefore, always check the frequency sensitivity of the UPS you’re going to buy. It should be able to withstand some amount of frequency variations.

Harmonic Distortion: The mains voltage is in the form of a perfect sine wave alternating at a frequency of 50 Hz in India. Harmonics are multiples of this frequency that get superimposed on this sine wave and distort it from its original form. Various types of electrical and electronic equipment can cause this. 

THD (Total Harmonic Distortion): It is the ratio of the sum of the powers of all harmonic frequencies above the fundamental frequency to the power of the fundamental frequency. It’s usually expressed in dB, and the measurements for calculating THD are made at the output of a device under specified conditions. It can reduce the power factor, and distort the input sine wave voltage at its peak. A computer draws its power close to sine wave peaks, so a distorted sine wave will not be able to deliver the peak current that an ideal sine wave would. Therefore, the computer may get a lower voltage than it actually should. For a computer type load, a THD of around 10 percent is acceptable. THD can be measured, and it needs to be measured so that one can adhere to the international standards for EMI control.

Noise: Any disturbance that affects the mains voltage waveform is called noise. A motor running on a mains line for instance could cause spikes in the line voltage due to the sparks that occur in its brushes. These spikes get superimposed on the sine wave, and distort it.

Determine UPS rating

Once you’ve analyzed the power situation in your area, you could do power planning, and decide upon the UPS capacity you really need. One of the most important aspects here is the Power Factor. It is the ratio of the effective power (watts) to the apparent power (volt-amps or VA). Mathematically put:

Power Factor = Effective Power (Watts) / Apparent Power (VA)

In other words, effective power equals Power Factor multiplied by apparent power as: 

Effective Power for Light Bulbs = Power Factor x Apparent Power (VA)

Resistive loads, such as light bulbs, have a power factor of unity, so its apparent power VA is equal to the effective power in Watts. Computer load, however, is non-linear in nature, so its power factor is less than unity. If a lower Power Factor rating is plugged into the above equation, the Effective power consumed by the load is lower than its apparent power. Since most UPS ratings are in VA, you must know the actual power consumed by your load and its power factor to determine what UPS rating to actually go for. Usually, a Power Factor value of 0.7 is good enough for computer load. This means that if your projected load is 100 VA, the actual power consumption for it is around 70 Watts (Power Factor x VA). This will also determine the actual battery ratings you need, so you don’t end up paying extra for higher rated batteries.

Choose deployment location and deploy

If it were a distributed system where small UPS units are scattered throughout, they are usually kept under the table. Don’t ever keep them next to the monitor to avoid the flickering of the screen. Also keep them away from any medical equipment like those for imaging and X-ray. In case of a slightly larger UPS, say 50 kVA or above, you’ll need extra space for the batteries. You’ll also need to plan for extra air conditioning since batteries generate a lot of heat. Besides the physical positioning, geographical location is also important in UPS selection. Very dry climate can cause static discharge, which can be bad for any electronic circuitry. Similarly, a very humid climate can cause short circuits. On the physical location front, make sure that 


Which should I choose-offline, line-interactive, or online? 
The choice of a UPS technology depends on how critical is the load you want to backup and the level of uptime you require. This is because different technologies cater to different specifications. 

The most common is the offline or standby technology which is suitable for handling single PC/workstation type load. When going for this, always check whether the UPS supports AVR (Automatic Voltage Regulation). 

Line-interactive UPSs are slightly more advanced than their offline counterparts. They monitor the incoming voltage, whether it’s too low or too high. Depending on this, they either buck or boost the voltage supplied to the PC load. They are good for providing backup for small network environments. 

Online UPSs offer the best form of protection as they completely isolate the load that they handle, from input power disturbances. 

Can UPS software help?
Many UPSs come with management software. Every UPS connects to a PC/Server through a RS232 cable. You have to load the software on this machine, which then monitors the condition?? of the UPS. The basic function of this software is to safely perform unattended shutdown of the machine in case of a prolonged power cut. More advanced software provides other useful information about the UPS such as the input/output voltage, battery charge, etc. Larger UPSs even support the SNMP (Simple Network Management Protocol), which allows you to manage them remotely over a network. 

Which UPS rating should I buy? 
For this, you’ll have to take a stock of how much power is consumed by the load you want to back-up. This load could be any IT equipment like a PC, monitor, printer, hub/switch, etc. You need to check the electrical specs of the load, and then do some calculations. See the box on ‘deploying a UPS’ for a more detailed explanation on how to do this.

When should I replace the UPS batteries?
Typically, most small UPSs use SMF (Sealed Maintenance Free) batteries, which last two to three years. Plus, most batteries come with a replacement warranty that mentions this duration. Check with your UPS vendor for warranty on the UPS as well as the batteries. If the backup time offered by the UPS drops below the specification given by the vendor, there could be a problem with the batteries.

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