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FAQ – Frequently asked questions

What features should I look for?

Some features you might look for include:

  • Sinusoidal power output. In general, the closer the AC output of the UPS is to a sine wave, the better it is for your equipment. Many UPS units, especially the cheaper ones, deviate a great deal from a sinusoidal output. Some of them generate square waves.
  • Batteries capacity: The larger the Ah rating, the more capacity the battery has – Most UPS brochures don’t discuss the Ah capacity of the battery directly, so you may have to look at a specification sheet to get the details as this has an important influence on the run time of a UPS.
  • Do the UPS have a manual bypass switch? If the UPS is broken or is being serviced, can you pass power through it to your equipment? The last thing you want is for a broken UPS to be the cause of extra downtime.
  • Some newer UPS can communicate with their monitoring software via a network connection and SNMP. This is wonderful if your network is on a UPS. Also, beware, some dealers advert “Network UPS” monitoring where the network is the normal serial connection.


What specifications should I look for?


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.

General Specifications:


  • UPS Type: The general design and typology of the UPS – It’s very important know what kind of UPS you are checking.
  • Load Rating: The nominal maximum capacity of the unit in VA. Many units will also specify explicitly the Watt rating of the unit; otherwise you need to determine the UPS’s power factor from the manufacturer to properly determine sizing.


Physical Specifications:


  • Dimensions: Check height, width and depth to make sure the unit will fit where you want it to go.
  • Weight: Some larger units are very heavy and may require a strong floor/platform where install it.
  • Number and Type of Receptacles: How many and what kind of output receptacles are provided to power loads.


Environmental Specifications:


  • Operating Temperature Range: UPS generate heat and cannot be run in a room with insufficient cooling.
  • Storage Temperature Range: Pay attention! Batteries can freeze or overheat and be ruined if subjected to excessive cold or hot temperatures.


Input Specifications:


  • Input Voltage: Nominal and actual allowable range specifications. Make sure you are getting the right model for your power utility range supply.
  • 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.
  • 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.
  • 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 indicators 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.


How important is the UPS output waveform?


A UPS should always provide the best approximation of sinusoidal output that one can, because any deviations produce harmonics which may either be interpreted as signal, and may actually damage the equipment.

A sinusoidal output UPS worth the extra money, especially for on-line UPS systems that continually provide their waveform to the equipment.

What can I do to maintain my UPS’s performance at its best?


There are some things you can do to decrease the likelihood that a UPS will trip you up. Here are some suggestions:

  • Perform regular maintenance on your UPS. This includes changing the batteries periodically. Don’t ever run on bad batteries.
  • Don’t deep cycle the batteries any more than is necessary.
  • Make sure the UPS keeps in contact with its electrical ground at all times.
  • Don’t subject the UPS to temperature or humidity extremes, water, excessive dust, or static electricity.
  • Keep the area around the UPS free, clean and dry.
  • Don’t overload the UPS.
  • If the UPS shows signs of misbehaviour or malfunction, remove it from service at the earliest possible opportunity. Don’t put it back into service until it has been examined and recertified by qualified support personnel.