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Given the same vendor claims, how can I tell a "good" quality UPS from a "poor" quality UPS?

The product differentiation is almost at near zero levels as majority of the vendors are importing UPSs from one country or the other. As a matter of fact with the implementation of BIS in India – the products that come to our country on single phase range is almost entirely from China and that too from 2-3 vendors.

The differentiation is realised by the customers based on the time taken to respond, time taken to delivery warranty and post warranty services, the total cost of ownership.

The very reason many major customers are looking at SPOC (single point of contact) model of services post warranty implies that the service levels delivered by popular brands are perhaps not meeting the customer expectation. This is more when the installation is spread across the country – which calls for a swift and agile organisation to respond to the needs of the customers quickly.

Field proven design and models is the key parameter that needs to be remembered instead of falling prey for superlative specifications.

The vendors ability to cover pan india and deliver predictable support and the experience the vendor has in this industry and the pre-sales approach of the vendor will clearly indicate the commitment and professionalism with which the vendors are serving in this industry.

Testing, testing, and testing. I can’t emphasize this enough. There are many good and bad units out there that call themselves UPS’s. There are many good units that are wrong for your situation. Caveat Emptor.

How long can equipment on a UPS keep running after the power goes?

UPS as a product is meant for Uninterrupted Power Supply. It is very often mistaken that a UPS can substitute a Generator. While there could be situations where installing a generator is not a possibility and power outages are for very long hours, where UPS with longer backup time becomes essential. But by and large – UPS shall always be used for power conditioning and enough backup time to ensure there are no abrupt interruptions in the process. The appropriate backup time can be arrived at after doing intensive pre-sales study uncovering various factors which may not have surfaced during initial process of buying a UPS.

One must also note here that just the UPS giving longer backup time but there is no sufficient lighting and fans running in the premises would still mean – the productivity cannot be achieved. The ideal solution would be a combination of Generator to handle prolonged power outages and UPS to deliver conditioned power and take care of delivering uninterrupted power. However based on specific situations – backup time requirements can be assessed during pre-sales process.

What sort of stuff does a UPS do?

A UPS traditionally can perform the following functions:

  • Absorb relatively small power surges.
  • Smooth out noisy power sources.
  • Continue to provide power to equipment during line sags.
  • Provide power for some time after a blackout has occurred.

In addition, some UPS or UPS / Software combinations provide the following functions:

  • Automatic shutdown of equipment during long power outages.
  • Monitoring and logging of the status of the power supply.
  • Display the Voltage/Current draw of the equipment.
  • Restart equipment after a long power outage.
  • Display the voltage currently on the line.
  • Provide alarms on certain error conditions.
    Provide short circuit protection.

How can it help me?

A UPS has internal/external batteries to guarantee that continuous power is provided to the equipment even if the power supply stops providing power. Of course the UPS can provide power for a while, typically a few minutes, but that is often enough to ride out power company glitches or short outages. Advantages:

  • Computer jobs don’t stop because the power fails.
  • Users not inconvenienced by computer shutting down.
  • Equipment does not incur the stress of another (hard) power cycle.
  • Data isn’t lost because a machine shut down without doing a “sync” or equivalent to flush cached or real time data.

Can you give me some more information on this?

The UPS industry is made up of many manufacturers, and there is a lack of standard terms within the industry. I think this sometimes borders on deliberate misdirection. (It’s a jungle out there!) [Note, in recent years the whole industry seems to have gotten better, at least mostly agreeing on what the terms listed here means. This is not true everywhere, but things are getting better. ]

There are basically three different types of devices, all of which are occasionally passed off as UPSs.

Standby power supply (SPS). In this type of supply, power is usually derived directly from the power line, until power fails. After power failure, a battery powered inverter turns on to continue supplying power. Batteries are charged, as necessary, when line power is available. This type of supply is sometimes called an “offline” UPS.

The quality and effectiveness of this class of devices varies considerably; however, they are generally quite a bit cheaper than “true” UPSs. The time required for the inverter to come on line, typically called the switchover time, varies by unit. While some computers may be able to tolerate long switchover times, your mileage may vary. [Some articles in the trade press have claimed that their testing shows that modern PCs can withstand transfer times of 100ms or more. Most UPS units claim a transfer time to battery of about 4ms. Note that even if a computer can stay up for 100ms, it doesn’t mean that 100ms switchover is okay. Damage can still be done to a computer or data on it even if it stays up. ]

Other features to look for in this class of supplies is line filtering and/or other line conditioners. Since appliances connected to the supply are basically connected directly from the power line, SPSs provide relatively poor protection from line noise, frequency variations, line spikes, and brownouts.Other features to look for in this class of supplies is line filtering and/or other line conditioners. Since appliances connected to the supply are basically connected directly from the power line, SPSs provide relatively poor protection from line noise, frequency variations, line spikes, and brownouts.

[Most SPS’s claim to have surge/spike suppression circuitry as well as transformers to “boost” voltage without switching to the battery if a modest voltage drop occurs. This, it is claimed, allows operation of the equipment indefinitely under brownout conditions as long as voltage does not drop below the lower cut-off voltage.]

Hybrid [or Ferro resonant] UPS systems.
The theory behind these devices is fairly simple. When normal operating line power is present, the supply conditions power using a Ferro resonant transformer. This transformer maintains a constant output voltage even with a varying input voltage and provides good protection against line noise. The transformer also maintains output on its secondary briefly when a total outage occurs. Manufacturers claim that their inverter then goes on line so quickly that it is operating without any interruption in power. Other UPS vendors maintain that the transition is less than seamless, but then again it’s not in their best interest to promote CVT based UPS products. CVT based UPS has a sizable part of the UPS market.

[Note: According to some sources, Ferro resonant transformers in an UPS system can interact with Ferro resonant transformers in your equipment and produce unexpected results. On the other hand, Ferro resonant UPS systems don’t kick off a lot of heat, which is important in some environments. The Moral: Again, test before you buy. ]

What I call “true” UPS systems, those supplies that continuously operate from an inverter. Obviously, there is no switchover time, and these supplies generally provide the best isolation from power line problems. The disadvantages to these devices are increased cost, increased power consumption, and increased heat generation. Despite the fact that the inverter in a “true” UPS is always on, the reliability of such units does not seem to be affected. In fact, we have seen more failures in cheaper SPS units. [Note, though, that given the same quality inverter, you’d expect the one that runs least to last longest. ]

What is a UPS?

An Uninterruptible Power Supply is a device that sits between a power supply (e.g. a wall outlet) and a device (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device.

What are the various types of problems encountered with power?

The various problems encountered are as follows:

Spikes are high-magnitude, split-second events that can disrupt computer operations and even damage equipment. Spikes can be caused by many things. The most important cause is lightning, which can strike on or near a power line or even miles away and cause huge jumps in voltage.

Other causes of spikes include switching large electrical loads on or off, utility switching, and static discharges. The most disastrous effect of spikes can be hardware damage. High-voltage impulses can blow holes in delicate micro-chip traces. Sometimes this damage is immediately apparent, but other times it is latent, not appearing until days or weeks after the event. Less catastrophic effects include corrupted data, printer or terminal errors, and data processing errors.

Surges are over-voltages that last longer than one cycle (1/60 second). Surges can be caused when some device on the line that has been drawing a large amount of power suddenly stops or is shut off. Surges can also be caused when utilities switch large loads off the line. Surges are more dangerous because of their duration, rather than their magnitude. Long or frequent surges can damage computer hardware.

Sags are the opposite of surges. They are multi-cycle under-voltage conditions. Ground faults, undersized power systems, and sudden start-ups of large electrical loads are all typical causes of voltage sags. Surprisingly, lightning is also a major cause of sags. Sags can be a serious threat to computers. If the voltage supply to the computer is inadequate, it can cause the computer to lock up. Sags can also slow the speed of disk drives, causing read errors or disk crashes.

Noise is a collective term for various kinds of high-frequency impulses that ride on the normal sine-wave. It can range from a few millivolts to several volts in amplitude. One especially troublesome problem is radio frequency (RF) noise. RF noise consists of high-frequency signals that travel on electrical wires. RF noise can be generated by lightning, radio transmissions, and computer power supplies. It can create erratic behavior in any electronic circuit. Noise can cause computer processing errors, incorrect data transfer and printer or terminal errors.

Brownouts are long-term under-voltages lasting minutes or even hours. They are often instituted by utilities when peak demand exceed generating capacity. Brownouts can cause computer malfunctions and hardware damage the same way that sags do, by depriving logic circuits and disk drives of the voltage they need to operate properly.

Blackouts are extended zero-volt conditions, lasting for minutes, hours or even days. They are becoming more frequent as the power distribution grid is increasingly overtaxed. Blackouts can be caused by ground faults, accidents, lightning strikes, or other acts of nature. A system crash is the most obvious effect of outages. Disk drives and other system components also can be damaged when power is suddenly lost.

Harmonics are distortions of the normal sine-wave. Harmonics are transmitted back into the AC line by non-linear loads (that is, loads that don’t draw power in regular sine-waves). Examples of non-linear loads are computers, copiers, FAX machines, and variable-speed motors. These harmonics can disrupt the operation of other devices connected to the AC line. Harmonics can cause communication errors and hardware damage. They can also cause transformers and neutral conductors in three-phase.

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