Size the standby battery for a fire alarm or emergency system: add the standby and alarm loads over their required durations, then allow for ageing.
Confirm the required standby and alarm durations, currents and ageing allowance against the relevant standard (e.g. AS 1670.1 for fire detection, AS 2293 for emergency lighting) and the equipment manufacturer’s data.
traqR keeps each system’s battery details and next service date on the site record, so replacements happen before they’re overdue.
Start free trialMultiply the quiescent current by the required standby time (often 24 hours) to get the amp-hours the system needs while simply monitoring.
Add the amp-hours for the alarm period — the higher current with sounders and strobes running, for the required alarm time.
Batteries lose capacity as they age and in the cold, so a derating factor (commonly 1.25) is applied to size the battery with margin.
Add the energy used during standby (quiescent current × standby hours) to the energy used in alarm (alarm current × alarm hours), then multiply by an ageing factor. For a system drawing 0.35 A in standby for 24 hours plus 1.8 A in alarm for 30 minutes, that’s about 9.3 Ah before ageing, or roughly 11.6 Ah with a 25% allowance.
They’re set by the applicable standard and the design. Fire detection and alarm systems commonly require 24 hours of standby followed by a period in full alarm (often 30 minutes), while emergency lighting under AS 2293 has its own duration requirements. Always confirm the figures for your system.
Battery capacity falls over its life and in low temperatures, so a battery sized for exactly the calculated load would fall short before its replacement date. A derating factor — commonly 25% — sizes the battery so it still meets the duration near end of life.
No. It’s a planning aid. Battery sizing, standby and alarm durations must comply with the relevant standard and manufacturer data, and the system must be installed and certified by a competent technician, with maintenance to AS 1851.
This calculator is a general engineering aid. Required durations, currents and ageing allowances depend on the applicable standard (such as AS 1670.1 or AS 2293) and equipment data. System design and certification must be carried out by a competent fire or electrical technician, with maintenance to AS 1851.
traqR keeps each system’s battery details and next service date on the site record. Try it free for 14 days.