Sizes a stationary lead-acid battery (vented or VRLA) for a DC system \u2014 substation control power, UPS, switchgear tripping supply \u2014 using IEEE 485's changing-load duty-cycle section method, which correctly identifies which period of a multi-stage discharge actually governs the required battery size (not simply the highest current or the longest duration alone).
Standards followed
IEEE 485 (recommended practice for sizing lead-acid batteries for stationary applications)IEEE 1188 (aging factor guidance)IEEE 946 (charger sizing, referenced for the advanced charger calculation)
What it can do
- Duty-cycle section-by-section required capacity, using the IEEE 485 section method (each load step weighted by its own Kt, not just the worst single period in isolation).
- Your own manufacturer's Kt (capacity-rating factor) table — IEEE 485 defines the calculation method, not the table itself, since Kt is product/chemistry-specific.
- Temperature, aging and design-margin correction factors producing the final required rated capacity.
- Advanced: random/intermittent loads added on top of the governing section, cell count & voltage window check, and charger sizing.
Example problem
This calculator's default scenario reproduces an illustrative 4-period duty cycle end to end, using the IEEE 485 section method.
- For each period, compute the net current (background load ± switching events).
- Apply the section method: Fₛ = Σ (Iₚ - I(p-1)) × Kt(Tₛ - T(p-1)), weighting each load step by the Kt for the time from the start of that step to the end of the section.
- Identify the governing (worst-case) section — the one demanding the largest required capacity, not necessarily the highest-current or longest one.
- Apply temperature, aging and design-margin correction factors to the governing section's capacity.
Governing section 4 requires 110.00 Ah; after ×1.00 temperature × 1.25 aging × 1.10 margin, final corrected capacity = 151.25 Ah.
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