How should I choose a UPS?

by Nyal Mellor April 08, 2013

The major considerations are:

• How much power does the UPS need to supply?
  In the event of a power outage the only devices you really need to keep on battery power are pieces of sensitive equipment such as projectors, computers and the like. To size the UPS add up the power consumption, in watts, of these devices. This information can be found in the manual, from your equipment manufacturer or by using a power meter. You should then compare this figure to the UPS rated capacity, which is also given in watts. We  recommend specifying a UPS that is rated for 150% of the load you need since most manufacturer’s quoted battery run time and THD performance is based on 50-75% load.
• How long does the UPS need to supply power for?
  A UPS is intended to allow for proper shutdown of connected equipment, not continuous operation. If you want to operate your system in an extended blackout then the solution you need is a generator not a UPS. 10-15 minutes of run time is generally  sufficient.
  
  

Additional considerations:

• Does the UPS output a true or stepped sine wave?
  Most UPS systems do not output a true smooth sine wave but something that looks more like a set of steps. A stepped sine wave is, by its very nature, high in THD. Switch mode power supplies found in computers and projectors are fine running on stepped sine waves but our recommendation is that all audio gear using linear power supplies (which is nearly all of it) is fed a true sine wave output with distortion below 2%. An important thing to note is that the UPS technology has nothing to do with what the output looks like. It is generally true that most standby devices output a square wave, most line interactive output a stepped sine and most online dual conversion ones output a true sine wave but this is not a rule just a reflection on the typical products available from most manufacturers.
  
  
  
  
• What is the audible noise level?
  Most UPS systems are designed for computer use where the audible noise created by internal cooling fans is not an issue. If you must have your UPS in your studio or home theater then pick one that has very low ambient noise levels.
• What is the level of powerline noise on the input and output sides of the UPS?
  The inverter found in UPS systems can produce a high level of powerline noise if not carefully designed. In a standby UPS this is not really a problem since all we want to do in an outage is safely shut down the system. Line-interactive and online UPS systems are always on, which means that noise performance is an important issue. Unfortunately manufacturers do not publish specifications on the level of powerline noise found on the outputs of their devices. Badly designed UPS systems can also couple noise to the input side, thus contaminating the powerline for all other equipment on the same electrical circuit.
  
  

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