UPS Battery Sizing Calculator
Calculate the battery capacity needed for an uninterruptible power supply to support a load for a specified runtime.
80% for lead-acid, 90% for Li-ion
Required Battery Capacity
28.9 Ah
Required Battery Capacity vs Desired Runtime
Formula
## UPS Battery Sizing Proper battery sizing ensures the UPS provides the required runtime at the expected load. ### Formula **Capacity (Ah) = (Load / Efficiency) x Runtime (hours) / Battery Voltage / DOD** Where DOD is the maximum depth of discharge (80% for lead-acid to extend life, 90% for lithium). ### Sizing Considerations - Battery capacity degrades over time (plan for end-of-life capacity) - Temperature affects capacity (reduce by 1% per degree C below 25 C) - Higher discharge rates reduce effective capacity (Peukert effect for lead-acid)
Esempio Risolto
2000 W load, 30 min runtime, 48 V battery, 90% inverter efficiency, 80% DOD.
- 01Runtime in hours: 30 / 60 = 0.5 hours
- 02Actual draw: 2000 / 0.90 = 2222 W
- 03Capacity: 2222 x 0.5 / 48 / 0.80 = 28.9 Ah
- 04Energy: 2222 x 0.5 / 0.80 / 1000 = 1.39 kWh
- 05Discharge current: 2222 / 48 = 46.3 A
Domande Frequenti
Should I oversize the battery?
Yes. Add 20-25% margin for aging, temperature, and Peukert losses. Replace batteries when capacity drops to 80% of rated.
Lead-acid or lithium for UPS?
Lead-acid is cheaper upfront but heavier and shorter-lived. Lithium costs more but offers 2-3x cycle life, lighter weight, and deeper discharge.
How does temperature affect UPS runtime?
Cold reduces battery capacity (typically 1%/C below 25C). Heat shortens battery life (halves for every 10C above 25C).
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