| Compare and select the best UPS for your application using Online UPS Features and Prices Guide |
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Online UPS systems grant the best power protection, but you need to know also the offered characteristic features and prices in
order to make the right choice.
Most people will tell you that you need to know UPS Type and Size in order to buy the right UPS, and Mavens will also mention
UPS backup time.
The said criteria are necessary to decide which system to buy, but they are far from being sufficient. Just as you wouldn't buy an
apartment based on size, location and price, without checking also rooms, directions, parking, age, lift, noise, neighbors etc, you
shouldn't consider buying a UPS without exploring also additional factors, which differentiate between the various offered UPS
systems.
UPS type is the first thing to consider, you can select between a Standby, Line Interactive or Online system. Stand by UPS
enables your computer to continue working for a limited time from batteries in case of power failure, but it doesn't protect the
computer from mains deviations and transients. Line interactive UPS provides protection also from limited line disturbances,
whereas On Line UPS grants the best power protection and is generally the preferred type for professional and critical
applications, and the only solution for high power systems.
Size in Volt Ampere (VA) or kVA (thousand VA) units is derived by multiplying UPS voltage by the nominal current, which the
UPS can supply. UPS current or VA capacity should be above the current or VA total sum of all protected consumers.
VA doesn't suffice to define the needed UPS size. You should also make sure that UPS real Power measured in Watt units is above
the Real power which your consumers require. In addition only the Real power affects backup time, and therefore this rating, as
well as additional UPS features should be compared, before coming to a decision.
Here are the main additional questions which should be considered before buying:
1. What is the Wattage rating of the UPS?
Apparent Power measured in VA units and Real Power measured in Watt units, define UPS size; both should be above the
respective total requirement of the consumers which the UPS protects.
Real UPS power equals VA multiplied by Power Factor ( PF) rating of the UPS, which has commonly 0.7, 0.8 or 0.9 rating.
Thus 5kVA (5000 VA) UPS with 0.7 PF rating can supply only 3500 Watt load, whereas same VA with 0.9 PF UPS can supply
4500Watt load.
Backup time depends only on Wattage. Thus, backup time comparison should be made with the same PF rating. The said 5kVA
units, each having a stated 5 minutes full load rating provide different backup times when connected to the same load. A 3500
Watt load that has 5 minute backup rating when connected to 0.7 PF UPS, renders above 70% more backup time when connected
to a UPS that has the same VA rating but 0.9 PF rating. .
2. What is the Efficiency of the UPS?
Online UPS efficiency is typically 87% to 96%. The wasted electric energy, associated with poorly efficient UPS types, might
double initial UPS cost within a few years, and should be considered before buying.
3. Does it have an Eco Mode operating regime?
Some Manufacturers offer online systems with Economy mode ability, which is a standby regime operation, where the load is fed
from mains with automatic transfer to Online operation if Line voltage deviates beyond set limits. The Eco mode may provide the
best of all solutions in a stable grid environment. It offers high, 96% to 98% efficiency in normal operation, as well as online mode
features at power outage, or when working from generator.
4. Can UPS systems be paralleled for increased power or redundancy?
Some online UPS systems have paralleling ability, thus increasing total output power capacity. Paralleling ability enables to order a
system sized for current Power requirement, increasing the installation when requirements grow.
Paralleling ability is also implemented in redundant UPS configuration where at least one surplus unit is added, beyond the required
capacity. A 20KVA load for instance, if protected by three UPS units of 10kVA each, in redundant configuration, will continue to
supply full load, even if a single unit fails. The small light weight UPS that failed, can be rapidly replaced or sent to repair without
affecting load protection.
5. Are UPS Batteries, user replaceable?
UPS system's ability, to protect load when power fails, depends on the health of its batteries. Batteries are the weakest link in an
online system; short battery lifetime and high quantity of series connected batteries make such UPS vulnerable to battery failure.
User's ability to replace failed batteries, may affect dramatically the time needed to restore UPS operation, as well decreasing
maintenance costs.
Some systems feature hot swappable batteries, which are installed in a battery cartridge, which is easily replaceable, without
turning the UPS off
6. Is the UPS equipped with a Maintenance By-Pass?
UPS systems are complex, computer controlled, power converters working from mains or batteries, which may and do also fail.
Utility mains voltage is available in 99.9 % of total time in western countries. But, due the inherent nature of Standby or Line
Interactive systems, a failed UPS is frequently revealed at the worst possible moment, when the utility fails and the load is
switched to UPS operation.
On Line UPS systems work continuously through their double conversion path. The UPS when failed transfers the load smoothly
to mains, initiating an alarm signal, which notifies the users that correcting measures are required to restore the system to normal
operation.
Statistics indicate that the main cause of power failures, which affect consumers working from On Line UPS systems stem not
from UPS failure but because of human interference.
Maintenance personnel called for minor issue or while performing preventive maintenance, cause due to diverted attention, lack of
knowledge, mistake or accident a total power failure which drops, sometimes damages all consumers that should be protected by
the UPS.
The Maintenance By Pass (MBP), is an internal manually operated transfer switch, that enables smooth transfer of consumer
loads to the mains, before starting UPS maintenance procedure. The switch enables to isolate the critical loads from the UPS, as
well as the technicians' power to cause damages.
7. Price and Performance.
The said considerations indicate factors, which should be considered when buying a UPS. Consideration of UPS Wattage rating is
always required for ascertaining that UPS capacity meets current and future consumer's requirements.
Cost sensitive approach should take in account the efficiency of the UPS and its ability to work in Eco mode.
Items 4 to 6 are related to the reliability of the UPS and availability of power to the critical load.
Intelligent UPS buying selection can only be based on comparison of UPS Prices and features.
In order to assist users to make the right selection taking in account the indicated points as well as additional factors, may be of
major importance in certain application, UPSonNet presents: " Online UPS : Price and Feature comparison guide" . The guide
enables users to compare prices and features of 1kVA to 10kVA single phase systems from main UPS supplier, providing also
manufacturer's contact links for purchase or consultation.
Proceed to: Online UPS : Price and Feature Comparison Guide