| 10 Questions to ask before buying a UPS |
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| Written by Administrator | ||
| Tuesday, 06 December 2005 | ||
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This guide is designed to give you the facts you need to purchase a UPS system for your home/business. To understand why you need a UPS we need to tell you a little bit about electrical power. We all know what a blackout is -- a sudden loss of mains (AC) power. But equally dangerous are some things you may be less familiar with, such as spikes, surges, brownouts and blackouts. It is almost impossible to get natural "clean" power all the time. Following are some of the problems that can plague (and destroy) our valuable data and equipment: Surges and Spikes - basically, a sudden extra burst of power through the mains line. This can be caused by electrical grid disturbances or even by lightning strikes. This temporary voltage increase might last just a few thousandths of a second, but can push the current to your system from 240V up to a massive 1000 volts or more. Damage can vary from lockups and data corruption to total system failure and damaged hardware (CPU, motherboard, RAM, hard drive, power supply unit etc). Spikes, (also known as transients or instantaneous surges) are not as strong as surges. Being subjected to surges and spikes can take its toll on your PSU and other components over a period of time, leading to eventual failure. Sags and Brownouts - these are usually very short-term drops in power (often characterised by the lighting dimming or flickering momentarily). During a brownout the voltage level "dips", then returns to normal. They are very common and can cause hardware crashes and occasional hardware damage, but can also lead to a range of problems that you may not suspect to be related to your PSU. This can include: your computer locks up or reboots for no apparent reason; data files become lost or corrupted; your CMOS setting has been lost; the image on your screen becomes discoloured or distorted; you occasionally get error codes when trying to read files. Lightning Strikes - the damage potential from being struck by lighting is obvious. A lightning strike can deliver a million volts of power instantly and a direct strike can destroy even a UPS-protected system. Thankfully, direct strikes are rare, but you don't have to be hit by lightning, or even have it strike nearby, to suffer damage to your equipment. A strike several kilometres away can still push dangerous voltage surges along underground wires and to your mains power cord and your telephone line. A good UPS can protect both power and telephone line connections to your computer equipment. TIP: If in doubt, the best protection is to simply shut down and unplug your equipment till the storm passes. But remember to unplug your phone connection also! Blackouts - A blackout, or power outage, is when the power fails totally. Without a suitable UPS, a blackout results in immediate shutdown. The damage can vary, depending on what your system was doing at the time. If your system was idle, the damage could be little or none. If you were working on files then anything held in temporary memory (RAM) will be lost, and major problems could result, especially if the computer was updating critical system files at the time. Note, also, that in an outage, the power often doesn't cut out cleanly. Damaging spikes and irregularities can occur when the power cuts out and when it comes back on again. Line Noise - this is characterised by small ongoing variations in the voltage level. A certain amount of line noise is normal and can be dealt with by a system's PSU. However, in some areas this can cause periodic and severe power problems. Noise can be generated by nearby equipment on the same power circuit or by nearby devices, such as heavy machinery, motors, radio transmitters etc. Noise can cause software/hardware lockups and data corruption and physical damage. These terms all have to do with either too much power or too little. Either condition is bad for your systems, and can be prevented by a properly sized UPS. 2. How it works? A UPS, in its simplest form, is a battery backup that takes over supplying electricity to your systems in the event of a power loss. Usually, a UPS is a separate box that sits in the power chain between the source of power (eg, a standard power point) and the rest of your systems. The UPS protects every other piece of equipment that is plugged into it. It is designed to prevent spikes, surges, sags and blackouts from reaching your valuable equipment. Being first in line, the UPS receives electrical current directly from the power outlet. When mains power is present, the UPS provides filtering (frequency regulation) of small fluctuations to ensure that a continuous supply of "clean" power is fed through to your equipment. When AC power fails, the unit uses its internal battery to supply back-up power without interruption. A typical UPS will power your system for 15-30 minutes, depending on its size (capacity) and the amount of equipment connected to it. Many, if not most, blackouts last for under one hour and while a good UPS will give you enough power to gracefully shut of your equipment during the first few minutes of the blackout, a more powerful unit can give you a "run time" long enough to ride through the entire outage. This will cost you more, of course, and you will have to plan your battery capacity appropriately. Some larger units can take extra battery packs to increase their run time. 3. What are the types of UPS? There a three different types of UPS all suitable for different tasks, and supporting different types of load. Here are explanations of the different technologies, along with their advantages and disadvantages. Hopefully it will help you decide which type of UPS is suitable for you:
Advantages: Low cost Disadvantages: Line-Interactive UPS
Advantages: Lower cost than online Disadvantages: Fluctuations, such as spikes, can still be passed straight to the load
Online / Double Conversion UPS
The UPS converts the 230V input AC mains supply to DC power which is then used to charge the battery. The DC current flow is then fed through an inverter stage which reconstructs the 230V AC mains output. Because the AC output is completely regenerated, it will be completely free from any mains-borne interference such as spikes and voltage variations. The output voltage and frequency is controlled precisely, thus ensuring a clean and stable sinewave power output. Online UPS are able to withstand large fluctuations on the input voltage before transferring to battery power (typically 276V-184V) thus eliminating unnecessary battery discharges. Upon mains failure, transfer to battery power is seamless ? no break. Online UPS also have various failsafe and self-diagnostic features that will instantly transfer the load onto mains power if there is a failure within the UPS hardware, or if the UPS is overloaded. Advantages: Continuous & total power conditioning Disadvantages: Because of the technology used, online usually costs more than other types of UPS technology 4. Which type is suitable for me? The choice of UPS type for your equipment depends on several factors: the type of equipment you have; the number and size of equipment pieces to be protected (each possibly drawing a different amount of current); the features you require (eg, communication port and smart software); and the length of "uptime" you want in the event of an outage. Sizes and specifications of various units vary tremendously, so you need to carefully consult the specifications for each make/model you are considering, taking into account the amount of power your combined equipment will draw and the time that this equipment needs to be supported. Allow a generous safety margin. On-line units offer the most protection, since they run constantly. The additional cost of these systems is often deemed worthwhile for key equipment where a shutdown is unacceptable. They are usually recommended for mission critical applications such as phone systems or a computer server. Standby and line-interactive UPS are more appropriate when an unexpected power outage, and the resulting loss of data or other information, would be more of an inconvenience than a major problem. These systems should be able to keep equipment going during most power fluctuations, but there may be the occasional situation where they do not quite work as expected. They can be a more cost-effective solution for equipment such as standalone computers or a fax machine. Line-interactive UPS are best suited for situations where power fluctuations are common occurrences. Power fluctuations occur when "power-hungry" equipment such as an air conditioner is frequently turned on and off, causing brownouts and surges. With line-interactive UPS, these fluctuations can be handled by the transformer instead of the internal battery. Even a well-designed, off-line UPS can transfer ac power from off to on in 1 to 4 ms, which it is truly uninterruptible because the connected equipment encounters 2 ms interruptions 120 times per second because of the incoming sine wave from the utility. If cost is a major factor, the off-line UPS is less expensive, followed by the line interactive and on-line UPS. Choose the right UPS technology for your situation; for simple power outage protection, off-line is the most economical type of system, and online is recommended for larger system applications. For business / personal computers we recommend Line Interactive UPS. 5. What are Waveforms and What's right for me? There are basically three waveform types used with UPS systems for use with microcomputers. They are 1. Square wave 2. Sine wave 3. Quasi-sine wave pulse width modulated (PWM) stepped rectangular wave.
All three types of waveforms must be tightly frequency-regulated and limit the maximum output average or RMS voltage to safe levels. This is necessary to prevent overheating of the computer power supply, especially for on-line UPSs. Although this is not as critical for standby units it is a very desirable feature. The square wave is the least expensive waveform to generate, the quasi-sine wave pulse width modulated stepped rectangular waves is the next higher cost, followed by the higher priced sine wave units. Sine wave units use the same principles as square and stepped waveform units but they add an additional filtering device or transformer on the output to convert the waveform to an approximate sine wave. Square waves, and quasi-sine wave pulse width modulated stepped rectangular waveforms are better sources for rectification into smoother more ripple-free dc voltage than do sine waves. The reason is that these waveforms have a higher average output voltage value and the output voltage is at peak value longer than for sine waves. The charging of a dc power supply occurs at the peak of the waveform. Thus, "flat-topped" waveforms are at the peak longer so they keep the dc supply input fully charged longer and thus produce a smoother dc output, which reduces ripple and improves the system power factor. However, if a large computer system employs ac motors, the sine wave approach is best. 6. How much power I need from the UPS? An important consideration for selecting the appropriate UPS is the determination of what "size should be selected. Most UPSs are rated by the maximum VA (volts ? amperes) they can deliver. VA rating is not the same as the connected equipment's power drain (in Watts). The computer's power factor, which is Watts/VA may be as low as 0.6, meaning that if you record a drain of 100 W, you need a UPS with a VA rating of 167. Some literature suggests that 0.7 may be a good conversion factor, but this depends on the machine. Note: Some UPSs can continue to deliver power if the VA rating is exceeded, they just can't go beyond their VA rating. Some can't provide power above their VA rating at all. It is generally recommended that a UPS have a capacity that is at least 25% greater than the total power capacity requirements of the connected equipment. For example, a desktop computer that runs between 300 VA to 400 VA should be equipped with a 500 VA UPS. You can check how much power your equipment uses by reading the plate on the back of the equipment. Keep your calculator handy, since these plates won't necessarily list the power requirements in the VAs that UPSes use. If the power figure is given in amps, just multiply by the line voltage (In India, that's usually 230V). Then add up the various pieces of equipment together. That means, if your computer is equipped with one HDD & One CD Drive with one or two PCI cards, you need 350W power supply which can be produced by a 500 VA UPS. (500/0.7). If you have 2 HDDS, 2 CD Drives with Lan, Sound & Graphics cards you need at least 450W power, which can be delivered using a 650VA UPS (650 *0.7). 7. H Careful selection of nominal battery voltage may be one of the most important considerations. With the present state of the art and economics in the battery industry, valve regulated lead acid batteries are the clear choice for commercial UPS in this power range. The same technology and economic considerations suggest nominal battery bus voltages of 12V increasing to 48V are the most appropriate choices for UPS ratings of 200VA increasing to 3kVA. This low battery voltage is a key element in the selection of the power switching elements. And the UPS batteries must not be like inverter batteries and be sure to check the UPS has maintenance Free lead-Acid Batteries. 8. How much Backup Time, the UPS can produce? UPS are available in the Indian Market which can power up a computer system from 2 Minutes to 12 Hours. Most UPS units are designed to provide about ten minutes of backup power. This should be enough time to appropriately shut down the connected equipment and avoid data loss. Since blackouts typically last no more than two minutes, this should also be enough time to work right through most power failures. (It should be noted, however, that this action is not recommended.) Manufacturers report how long a battery will last under full-load or half-load conditions. Running under full load signifies that a UPS is working at its maximum capacity. A typical UPS should report a full-load time duration of about ten minutes. Under half-load conditions, when the UPS provides only half the power it is capable of generating, the time duration is often more than three times as long. The backup time of the UPS depends on the 1. Internal Battery type (12v or 24v) 2. Current Driven to the battery 3. Output Load (No of equipments connected to the UPS) 9. How it interface with my Computer
There are two types of interfaces available now, RS232 and USB. USB connectivity is the advanced one which is easy to maintain comparing with serial port. Check whether the UPS monitoring software provides the Battery Status and automatic system shutdown / hypernate.
10. Other useful features you should consider before selecting the UPS brand Operating Frequency Range Operating Voltage Range Operating Temperature Range Surge Protection AVR (Automatic Voltage Regulation) Data Line Protection (For Telephone/ Modem / Lan Surge)
 External battery Support (Useful to extend the backup time) Number of A/C outlets Protected bypass Outlet (Useful for devices that not require battery backup)
Cold Start (Switch on the UPS, when there is no input power) Overload Protection Automatic Restart Battery Recharge Time Warranty for electronic & batteries Copyright: IT Portal.org
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| Last Updated ( Tuesday, 06 December 2005 ) | ||
Uninterruptible power supplies (UPS) are designed to protect electronic equipment like computers and phone systems against problems stemming from a temporary failure in the power supply. By providing a constant source of electricity, a UPS can help prevent damage or data loss that can occur with the unexpected shutdown of computers, phone systems, and other sensitive equipment.
Off-line or standby UPSs normally connects the equipment directly to the ac line with the battery and inverter held in a standby mode. If there is an ac powerline disturbance, it employs the internal battery and inverter to generate ac for the connected equipment. When the line returns to normal, the connected load automatically switches back to the ac powerline. Typically there will be a break of between 4-10 ms during the transfer to and from the battery mode. 
A line-interactive UPS operates in a very similar fashion to an offline UPS, except with the advantage of better filtering and output voltage boost/reduce features. Line-interactive UPSs provide basic power protection at mid-range prices. They protect against power disturbances, power sags and power surges, brownouts and electrical line noise. This design offers low-grade voltage regulation by "bumping" the utility voltage up or down before passing it through to the connected system. During the UPS voltage changes, the line interactive types use the battery for regulation. Although line-interactive UPS provide more voltage regulation than off-line UPSs, battery life is often sacrificed. 
On-line or continuous UPSs convert the incoming ac power to an internally generated ac that continuously supplies power for the connected equipment. If there are ac power disturbances, it employs its internal battery and inverter to generate ac for the connected equipment. When utility power comes back, it transfers back to its internally generated ac derived from the ac power line. 
ow to know the UPS has good Batteries?
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