The Online UPS has some specific features, such as Eco mode operation that grantsyour devices the best power protection and optimize your battery for lifetime. Additionally it acquires low running costthat is achievable normally with lower priced Off Line, UPS systems.
The off Line UPS systems(Uninterruptible Power Supplies systems), includes the Line Interactive types which are frequently preferred over Online UPS types for small office or datacenter applications as it has justified on the basis of lower procuring and running costs but it relatively gives poorer protection.
This approach ignores the existing differences between Online UPS systems, like the ability to operate in Economic (Eco) mode. This Eco mode may offer better power protection at lower cost. The simple off Line UPS systems, connect the load to the input AC line directly.
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.
Off Line types, including Line Interactive systems offer higher efficiency when compared to an Online UPS due to its direct connection to input AC power. 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 operationwhich ultimately decreases drastically the battery life time.
An Online UPS that is also called Double conversion system, converts the AC input voltage to stabilized DC first of all and then it is converted back to AC, to feed continuously the critical load, with a pure stabilized sinusoidal output that would be coming either from the input line via AC/DC converter, or from the batteries it is a 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.
However, recently the online UPS systems with Eco (economic) mode operating regime are offered by numerous manufacturers 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 generally works on mains even in unstable grid environment with some of the frequent transfers to battery as explained. However, an online UPS in a similar environment will be behaving similarly if it is set to Eco mode. But here, most of the described hazards can be avoided if you have selected the Double Conversion mode, in the unstable grid season.
You’ll witness some cases where UPS systems will automatically change the working regime of the online UPS to online operation, even if you’ve selected the Eco mode, if it senses the unstable utility environment.
The gain that has been associated with Eco mode is quite tempting. But by offering both best protection and high efficiency make it 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. The implementation of which is mainly software based, and the manufacturers prefer it to be competitive but not to increase online UPS price. Therefore, online UPS Systems with Eco mode should be preferred unless& until other considerations prevail.