Calculation sequence
Step-by-step method
- Calculate nominal DC energy.
- Apply user-entered usable depth and conversion efficiency.
- Divide ideal usable energy by constant AC load.
ElectricalIntermediateStandby Power and Batteries
UPS Battery Runtime Screening Calculator
Estimate ideal usable runtime from nominal DC energy, usable depth, conversion efficiency, and constant AC load.
Why it matters: A transparent energy balance supports early screening while keeping final runtime tied to exact discharge data.
Calculated result
Engineering evaluation
Ideal battery runtime (t)1.728 h
- Nominal stored energy (Eⁿ)
- 24 kWh
- Ideal usable AC energy (Eᵘ)
- 17.28 kWh
Engineering interpretation
The ideal energy balance gives 1.728 h (103.68 min) runtime.
Important limitations
- Ideal screening only. Exact manufacturer discharge data are mandatory for final use; temperature, aging, discharge rate, end voltage, reserve, redundancy, and topology are omitted.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
Eⁿ = Vᴰᶜ·C/1000
Eᵘ = Eⁿ·DOD/100·η/100
t = Eᵘ/Pᴸ
Current substitution
Eⁿ = 240×100/1000 = 24 kWh; Eᵘ = 17.28 kWh; t = 17.28/10 = 1.728 h.
Equation legend
Inputs and calculated quantities
- Vᴰᶜ
- Nominal DC voltage — V
- C
- Rated battery capacity — Ah
- DOD
- Usable depth of discharge — %
- η
- UPS/inverter efficiency — %
- Pᴸ
- AC load — kW
- t
- Ideal battery runtime — h
- Eⁿ
- Nominal stored energy — kWh
- Eᵘ
- Ideal usable AC energy — kWh
Applications
How this calculation is used
Building design
Screen a nominal runtime relationship.
Construction
Check battery voltage, capacity, and UPS efficiency inputs.
Commissioning
Compare an ideal screen with manufacturer runtime and discharge curves.
Quality controls
Assumptions and limitations
Assumptions
- Nominal voltage, load, efficiency, and usable capacity remain constant.
- Entered Ah capacity is applicable to the discharge rate for this ideal screen.
Limitations
- Ideal energy-balance screening only; exact manufacturer discharge data are mandatory for final use.
- Temperature, aging, end voltage, rate effects, duty cycle, reserve, redundancy, and topology are omitted.
Field use
Verification procedure
- Follow the approved electrical-safety program and use correctly rated instruments.
- Confirm wiring, ratios, units, operating mode, and measurement boundaries.
- Document simultaneous readings and compare with approved project and manufacturer data.
Common engineering mistakes
- Combining values from different time intervals, phases, or measurement boundaries.
- Treating a screening result as equipment selection, protective-device coordination, or code compliance.
Technical basis
References and source standards
- IEEE Standards AssociationPower quantity, harmonic, transformer, motor, battery, and metering standards; verify the current applicable edition during professional review.
- NIST Guide for the Use of the International System of UnitsElectrical quantity, unit, symbol, and conversion context.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement