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| APC Line Interactive UPS & APC Standby UPS products Guide |
Recent movement towards a green world affects also computer server regulations, such as
Energy Star, which demand to include Active Power Factor Correction (APFC) circuits in
computer servers in order to decrease losses and grid pollution.
Introduction of these new computer types has immense significance on UPS selection,
utilization and specification, particularly as related to the following two points which should be
considered when specifying a UPS:
1. Required UPS Power to protect new computers.
When specifying a UPS, its Apparent (called also Total) Power measured in VA
( Volt –Ampere) units and Actual (called also True) Power ratings should be above the
respectable figures of the computers powered by it.
A typical Watt rating of a UPS is 70% of its VA rating, whereas the Wattage rating of
computers with APFC is almost the same as its VA power. Hence, a 1000VA UPS for
instance, is able to deliver only 700Watt, whereas a new 1000VA computer requires 1000Watt
UPS. The size of a UPS should therefore be selected to comply with computers wattage
rating. In the specific example the UPS should be increased to at least 1430VA in order to
supply the 1000Watt required by the computer.
2. Required UPS Waveform to protect new computers.
UPS output waveform should be compatible with new computer requirements, which are
designed to work from a sinusoidal input waveform. Non sinusoidal voltage sources are prone
to drop load when powering computers with APFC circuits.
Standby and Line Interactive UPS systems power the critical load from utility line, as long as it
is within specified voltage window. Both systems are equipped with a standby inverter
connected to UPS battery, which kicks in to support the critical load via the inverter from
battery, whenever utility power fails or deviates beyond the voltage window boundary.
Online UPS systems have generally an Inverter with sinusoidal waveform like the utility line.
But, the waveform of most Inverters in Standby and Line Interactive systems, is a square or
pulsed type, called modified sinewave, semi sinewave or stepped sine wave. These
waveforms, work properly with conservative computer power supplies, but may not be
tolerated by new computer power supply designs.
A computer with APFC works properly when powered from the utility. But the exact behavior
when the utility power fails and the load is switched to Inverter operation, with non sinusoidal
inverter depends on the particular power supply design. Load can drop either due to computer
power supply shut down when connected to such Inverter, or due to UPS shut down because
of overload occurring when the UPS switches from line to inverter. For more about it , see
our newsletter
Most users are still unaware of the problem, discussed mainly on users' forums. Whereas the
amount of computers with APFC circuits is continuously growing, due to computer
manufacturer's effort to comply with regulations. For more about this issue see our June
2010 Newsletter topic: UPS Waveform and New Computer Servers. More about it see
UPSonNet June 2010 Newsletter titled: UPS Waveform & New Computer Servers
Using the Guide
The guide displays main specifications and features of APC Line Interactive and Standby 120V
UPS systems. For more information about these types see UPS Basics.
Consult UPS Glossary, for basic description of terms.
APC ystems were selected based on dominance in the low power single phase market. Similar
considerations apply to other makes and voltages. See UPS Manufacturers list for systems
from other companies.
When selecting a UPS for particular application consider Total (Sum) Power in VA and Watts
of all loads which the UPS should protect, taking in account future needs. Total UPS Watt
Power and VA Power should be above the total corresponding load figures, with a safety
margin of at least 20%.
Next, proceed to detailed description and available selection options of: APC Line Interactive
and Standby UPS Product Guide