UPS Selection Guide

1. Obtain load details from the rating plate of the equipment to be supported.  This rating plate is usually located at the rear or base of the equipment.  Where the rating is given in terms of voltage and current (amps), multiply the two to obtain VA. i.e.: 240 volts at 1.4 amps = 240 x 1.4 = 336 VA. Sometimes the load is given in watts, if so, as a rule of thumb, divide given wattage figure by 0.7 to obtain VA. i.e.: 250 watts = 250/0.7 = 357 VA. Approximate loads for equipment are listed below.

2. Having determined the load in VA of each piece of equipment to be supported, add VA figures to obtain total load in VA, i.e.: 486 computer at 100 VA + 14" monitor at 50 VA + tape backup at 100 VA = 250 VA.  Determine if there are likely to be any future expansion requirements and add these to the current calculated load to obtain total VA requirement.

3. Determine backup time in minutes required and then choose a UPS to meet these requirements.  The Nikko UPS Selection Chart, located on this Website, can be used for this purpose.  From the Nikko UPS Selection Chart, the above loads of 486 computer, 14" monitor and tape backup, will be supported by a Nikko King Pro 425VA (KIN-425AP) UPS for 11 minutes or a King Pro 525 VA (KIN-525AP) UPS for 14 minutes and so on.  If, for example, a backup time of one (1) hour was required for these loads, a Nikko King Pro (KIN-1200AP) 1200VA UPS would be the nearest to meet this requirement and would provide 76 minutes of backup time.

4. Laser printers generally do not require to be supported off of a UPS.  Where they do, however, care should be taken in calculating the load of such devices. The rating plate of a laser printer might state, for example, 240 volts at 2 amps or 480 VA.  This only relates to the running load, however, for when the heater in the laser printer comes on the load will increase to around 5 amps or 1200 VA.  So a UPS for the laser printer alone would need to be rated at 1200 VA.  It is recommended that where it is not essential to have battery backup for a laser printer that the printer be protected by an active power filter or the like to provide protection from the effects of lightning and electrical noise.

5. If ratings are not available use estimates below.

Extended Run Time Calculator

As can be seen from the above, connecting a load to a larger than required UPS, will provide a longer backup time than if the UPS were fully loaded.  As an approximation, the following can be used to calculate the likely backup time from a larger than required UPS.

Divide the rating in VA of the UPS by the rating in VA of the load.  If the result is less than 1.3 these calculations cannot be used.  Where the result of the above division is greater than 1.3 but less than 3, multiply this result by 1.3 x the full load backup time of the UPS to obtain the backup time at the lower load.  Where the result is greater than 3 user a 1.5 multiplier.

Examples:

600VA UPS with full load backup time of 10 minutes.

Load of 250 VA.  600/250 = 2.4. So multiplier is 1.3.
Therefore, backup time for 250 VA load on 600VA UPS = 2.4 x 1.3 x 10 = 31.2 minutes approximately.

Load 120 VA.  600/120 = 5. So multiplier is 1.5
Therefore backup time for 120 VA load on 600VA UPS = 5 x 1.5 x 10 = 75 minutes approximately.

Easy Sizing Matrix for desk top computers