Learn about the technologies behind the Internet with The TCP/IP Guide!
NOTE: Using robot software to mass-download the site degrades the server and is prohibited. See here for more.
Find The PC Guide helpful? Please consider a donation to The PC Guide Tip Jar. Visa/MC/Paypal accepted.
View over 750 of my fine art photos any time for free at DesktopScenes.com!

[ 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 determine sizing.

Physical Specifications:

  • 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 move.
  • 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? ;^)

Environmental Specifications:

  • 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 Specifications:

  • 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 Specifications:

  • 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 power.

Battery Specifications:

  • 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.

Next: Comparison of Power Protection Methods

Home  -  Search  -  Topics  -  Up

The PC Guide (http://www.PCGuide.com)
Site Version: 2.2.0 - Version Date: April 17, 2001
Copyright 1997-2004 Charles M. Kozierok. All Rights Reserved.

Not responsible for any loss resulting from the use of this site.
Please read the Site Guide before using this material.
Custom Search