Selecting Stand-by Power Supplies

The stand-by power supply that you select must be large enough to fill your computer's power needs. SPS devices are rated in units called VA. The unit that your select must have a larger VA rating than your system. Check your manuals for this rating for the equipment you are operating. If you can't find it, look on the back of the equipment. For a personal computer system, this would be the CPU and monitor. Find the amps listing for each, and add them together, then multiply by 120. The resulting number is the VA rating for your system. Do not connect a printer to an SPS. The start-up current required for it will cause the SPS to fail. Once you have determined the size of your system you can begin shopping for the SPS. They are available from computer stores and mail-order magazines.

When selecting an SPS, you should look for these things:

  • Sufficient battery time to perform an orderly shut-down,
  • A switching Time of 2 ms to 12 ms,
  • UL listing,
  • Sine-wave output,
  • Output surge suppression,
  • An audible alarm to indicate a low battery, and
  • User replaceable batteries.

Some units have data connections directly to your computer to shut it down automatically if you are not there. These units will include special software that needs to be installed on your system.

Installing an SPS is very simple. With your system turned off, disconnect it from the outlet and plug it into the SPS. Then plug the SPS into the outlet and turn it on. You are now ready to turn on your system and begin work.

It is important to note that, even with an SPS, your system will still have very small periods with no power. For most PC systems, this is not a problem. For other equipment, it may be. It is best to contact your computer supplier prior to the purchase of an SPS to determine if your system will operate correctly when connected to an SPS.