Specific Online UPS features, such as Eco mode operation, offered by certain manufacturers, grant best power protection and optimized battery lifetime, as well as low running costs achievable normally with lower priced Off Line, UPS systems.

Off Line Uninterruptible Power Supplies ( UPS) systems, including Line Interactive types are frequently preferred over Online types for small office or datacenter applications, justified on the basis of lower procuring and running costs, in spite of relatively poorer protection. This approach disregards existing differences between Online UPS systems, such as the ability, of certain online systems to operate in Economic (Eco) mode, which may offer better power protection at lower cost.

Simple Off Line UPS systems, connect the load directly to the input AC line. Line Interactive systems have also the ability to correct UPS output if AC input voltage deviates beyond preset limits by means of an auto- transformer based Automatic Voltage Regulator. In case of significant utility voltage deeps or outages these systems transfer the UPS to battery operation.

Due to its direct connection to input AC power, Off Line types, including Line Interactive systems offer higher efficiency when compared to an Online UPS. But, unstable grid environment, such as exercised in summer due to air conditioning, or in stormy winter seasons with frequent power excursions or outages, might cause these systems to suffer from frequent transfers to battery operation. Thus, exposing the critical load to possible failures due to unsmooth or unsuccessful transfer, or to battery failure, because of numerous battery discharges, which decrease drastically battery life time.

An Online UPS system, frequently called Double conversion system, first converts the AC input voltage to stabilized DC, which is then converted back to AC, to feed continuously the critical load, with pure stabilized sinusoidal output, coming either from the input line via AC/DC converter, or from batteries in case of power failure.

The described Online Double Conversion topology, although providing best protection reduces Single Phase UPS efficiency to about 90% compared to 97%, achieved with Line Interactive systems. The added running costs, associated with lower efficiency may add about 10% per year to initial UPS cost, if cooling costs are disregarded.

Recently Online UPS systems with Eco mode operating regime are offered by certain manufacturers also for low power single Phase Online systems. The Eco mode operation, if selected, enables an Online UPS to work directly from utility mains transferring automatically to Online operation in case of outage or excursion beyond set limits of the incoming AC line.

There is however a big difference between the Line Interactive UPS and Online system working in Eco mode regime. An Off line UPS system MUST work continuously from mains using the battery backup mode for short backup times, while an Online system CAN work continuously in both modes.

A Line Interactive UPS, will work on mains even in unstable grid environment with frequent transfers to battery as explained. An Online UPS in a similar environment will behave similarly if set to Eco mode. But here, most of the described hazards can be avoided by selecting the Double Conversion mode, in unstable grid season. Some UPS systems will automatically change the working regime to Online operation, even if Eco mode is selected, upon sensing unstable utility environment.

The gain associated with Eco mode is quite tempting. By offering both best protection and high efficiency, it is a kind of best of all worlds’ solution. UPS systems with Eco mode feature, grant in average about 5% power saving, just considering UPS efficiency. Taking in account also cooling requirements, close to 10 % of wasted power can be saved, decreasing UPS initial investment by almost 20% per year, compared to normal Online UPS operation.

Worthy of note, the Eco feature doesn’t normally have a price tag. Its implementation is mainly software based, and manufacturer’s preferred competitive attitude is not to increase UPS price. Online UPS Systems with Eco mode should therefore be preferred unless other considerations prevail.

Author Bio: Meir Portnoy is VP of UPSonNet , a leading source of information about Power Conversion and UPS systems. For more information about Eco mode systems, as well as other important features offered by UPS manufacturers visit UPSonNet website, for: On Line UPS:Price and Features Guide.

Category: Computers and Technology
Keywords: Online UPS, UPS Eco, UPS price, UPS cost, UPS efficiency, Line Interactive UPS.