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KB450147 – Uninterrupted Power Supply Sizing

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Table of Contents


This article describes the process of sizing a UPS for your 45Drives Unit. A UPS is an optional addition to the unit.


  1. List all equipment to be protected by the UPS.(Remember to include monitors, external hard drives, routers, etc.) If it’s only the 45drives unit then the power requirements can be listed here.
  2. List the current (amps) and Voltage (volts) for each device. These ratings can typically be found on the label on the back of the equipment. Multiply Current (amps) by Voltage (volts) to determine VoltAmps (VA). Some devices may list their power requirements in watts. To convert watts to VA, divide the watts by power factor. For servers, the power factor is often 0.9.
  3. Multiply the VA by the number of pieces of equipment to get the VA subtotals.
  4. Add the VA subtotals together.
  5. Multiply the total by 1.2 to get the grand total. This step accounts for future expansion.
  6. Use the grand total to select a UPS. When choosing a UPS, be sure that the total VA requirement of supported equipment does not exceed the VA rating of the UPS.

Use the UPS Selector located here to choose one based on your units standing load.

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