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UPS Runtime Calculator

Estimate backup runtime in minutes during power outages for computers, servers, and routers connected to a desktop UPS.

VA
300 VA5,000 VA
W
20 W600 W
14
Calculation Results
Estimated UPS Backup Time
16 minutes
UPS Load Level: 41.7% of capacity
Backup in Minutes
16 min
UPS Load Percentage
41.7%
Continuous Load
250 Watts
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How to use the UPS Runtime Calculator

  1. 1Enter UPS rating in Volt-Amps (VA) (e.g. 600VA, 1000VA, 1500VA).
  2. 2Enter total connected load in Watts (PC, monitors, networking).
  3. 3Optionally specify internal battery capacity (e.g. 7Ah 12V).

How UPS Runtime is Calculated

Calculates load percentage against UPS inverter limits and computes discharge time from internal sealed lead-acid (SLA) cells.

Mathematical Formula
Runtime (Min) = (Internal Battery Wh × 0.50 × 0.80 / Load Watts) × 60
Formula Variables & Logic

Small line-interactive desktop UPS units are designed primarily for graceful shutdown windows (5-20 minutes).

Worked Example: Running a 250W Desktop PC on a 1000VA UPS
Sample Calculation
Scenario: A 1000VA UPS containing two 7Ah 12V batteries (168 Wh) powering a 250W PC setup.
Step-by-step breakdown
  1. 1Usable Battery Energy = 2 × 7 × 12 × 0.50 × 0.80 = 67.2 Wh
  2. 2Runtime in Hours = 67.2 / 250 = 0.269 hours
  3. 3Runtime in Minutes = 0.269 × 60 ≈ 16 minutes
Estimated Result
UPS runtime is approximately 16 minutes.

What affects UPS Runtime results

  • Battery age: SLA batteries lose up to 50% capacity after 3-4 years of continuous float charging.
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Frequently Asked Questions

Why does my UPS run for less time under high loads?

Due to internal chemical resistance and Peukert law, drawing high current from small SLA batteries dramatically lowers effective deliverable watt-hours.

Can I add external battery packs to extend UPS backup runtime?

Select enterprise and tower UPS units feature external battery pack connectors (EBMs) that allow runtime extension from minutes to several hours.

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