[ The PC Guide | Systems
and Components Reference Guide | Power | External Power | Uninterruptible Power
Supplies | Uninterruptible Power Supply Functions and Features
In this section I will briefly cover some of the more common specifications that you
will find associated with UPSes. UPS spec sheets can be long and involved, and in most
cases you don't need to worry about all of the different items you will find there.
However, some are critical to check before you make a purchase decision.
Tip: Some of the
electrical performance specifications provided in UPS manuals are the same or similar to
those provided for power supplies. This more detailed section
on power supply specifications may have a description of some electrical specs I have
not duplicated on this page. Also, since UPSes include surge suppression circuitry, you
may want to check this page for a listing of surge
suppressor specifications and features.
- UPS Type: The general design of the UPS. Very
important to check this first.
- Load Rating: The nominal maximum capacity
of the unit in VA. Many units will also specify explicitly the W rating of the unit;
otherwise you need to determine the UPS's power factor from the manufacturer to properly
- Dimensions: Height, width and depth. Check to make sure the unit will
fit where you want it to go.
- Weight: Some larger units are very heavy and may require two people to
- Number and Type of Receptacles: How many and what kind of output
receptacles are provided to power loads.
- Color: This is very important! You don't want to totally wreck your
computer's ensemble, do you? ;^)
- Operating Temperature Range: UPSes generate heat and cannot be run in a
room with insufficient cooling.
- Storage Temperature Range: Pay attention especially to the bottom end
of the range. Batteries can freeze and be ruined if
subjected to excessive cold.
- Boost Charge Interval: How often the battery will need to be recharged
if the unit is put into storage.
- Input Voltage: Nominal and actual allowable range specifications. Make
sure you are getting the right model for your neck of the woods!
- Nominal Frequency: Generally either 50 or 60 Hz. Some models will
automatically handle either.
- Input Connection: The type of plug the power
cord uses; very important for larger units.
- Output Voltage: Nominal and actual range specifications will be
provided. Nominal should be the same as the nominal input voltage. :^)
- Output Waveform Type: Whether the unit produces a sine, square, or
modified square output waveform.
- Transfer Time: An important specification: the typical and/or maximum
values for the time required for the UPS to switch from line to battery power. For a true
online UPS this will be zero. For standby units it will normally be a few milliseconds. See here for more details. You should compare this value to
the hold (or holdup) time specification of your
power supply unit, which represents the amount of time the power supply can handle having
its input cut off before being interrupted. If the transfer time is close to or larger
than the hold time, this UPS may not serve you well.
- Filtering, Suppression and Regulation Specifications: Details on the
hardware within the UPS used to clean up the power line when the unit is running on AC
- Battery Type: The type of battery and
whether it is user-replaceable.
- Battery Capacity: Battery capacity in Ah.
- Typical Battery Life: Number of years the battery is expected to last,
on average, in average use.
- Typical Run Time at Full Load: If the unit powers a load with a VA
rating equal to its maximum load, the expected number of minutes of run time.
- Typical Run Time at Half Load: If the unit powers a load with a VA
rating of half its maximum load, the expected number of minutes of run time.
- Typical Recharge Time: How many hours it takes to fully charge a
discharged battery from line power.
- Battery Expansion: What sort of expansion features the UPS has, and if
so, how they work.
- Indicators and Alarms: A short listing of the indicator LEDs on the
unit, and conditions which trigger alarms.
- Control and Monitoring Hardware and Software: A brief description of
any included or optional control and monitoring systems,
including a specification of the interface types supported by the unit.
- Certifications: Which certification
bodies have approved the unit.
- Warranty: Warranty period in years.
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