Battery size needed calculator
Equipment Power Usage
The power drawn by computing equipment is expressed in Watts or Volt-Amps (VA). The power in Watts is the real power drawn by the equipment. Volt-Amps are called the "apparent power" and are the product of the voltage applied to the equipment times the current drawn by the equipment. Both Watt and VA ratings have a use and purpose. The Watt rating determines the actual power purchased from the utility company and the heat loading generated by the equipment. The VA rating is used for sizing wiring and circuit breakers. The VA and Watt ratings for some types of electrical loads, like incandescent light bulbs, are identical. However, for computer equipment the Watt and VA ratings can differ significantly, with the VA rating always being equal to or larger than the Watt rating. The ratio of the Watt to VA rating is called the "Power Factor" and is expressed either as a number (i.e. 0.7) or a percentage (i.e. 70%).
Example #2: Consider the case of a 1000VA UPS. The user wants to power a 900VA file server with the UPS. The file server has a Power Factor Corrected power supply, and so has a Watt rating of 900W and a VA rating of 900VA. Although the VA rating of the load is 900VA, which is within the VA rating of the UPS, the UPS will not power this load. That is because the 900W rating of the load exceeds the Watt rating of the UPS, which is 60% of 1000VA or around 600W.
Ensure correct loading of your UPS
Equipment nameplate ratings are often in VA, which makes it difficult to know the Watt ratings. If using equipment nameplate ratings for sizing, a user might configure a system, which appears to be correctly sized based on VA ratings but actually exceeds the UPS Watt rating. By sizing the VA rating of a load to be no greater than 60% of the VA rating of the UPS, it is impossible to exceed the Watt rating of the UPS. Therefore, unless you have high certainty of the Watt ratings of the loads, the safest approach is to keep the sum of the load nameplate ratings below 60% of the UPS VA rating. Note that this conservative sizing approach will typically give rise to an oversized UPS and a larger run time than expected. If optimization of the system and an accurate run time are required, call our power experts who have the ability to accurately size your UPS.
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