Fire-Alarm / Security Standby Battery
Required battery amp-hours from standby and alarm loads times the aging/derate factor.
Example
You enter
- Standby (supervisory) current (A) 0.5
- Standby period (h) 24
- Alarm current (A) 2
- Alarm period (min) 5
- Derate / aging factor 1.2
You get
- Required capacity (Ah) 14.6
- Next standard battery 18
Details, formula, and sources
With the next standard size (NFPA 72 §10.6).
Ah = [(I_standby * h_standby) + (I_alarm * h_alarm)] * derate, with the alarm minutes converted to hours; the next standard battery size is the smallest at or above the requirement.
Secondary (standby) battery sizing for a fire-alarm or security control unit - standby amp-hours plus alarm amp-hours times the aging/derate factor - per NFPA 72 National Fire Alarm and Signaling Code §10.6 (secondary power supply) and the panel manufacturer's battery-calculation worksheet, by name.
First-principles amp-hour accounting. The AHJ-adopted NFPA 72 edition, the listed panel, and the battery manufacturer's derating govern.
Estimate. AHJ and licensed fire protection engineer govern.
Field names used by the API: standby_current_a, standby_hours, alarm_current_a, alarm_minutes, derate, required_ah, next_standard_ah
- Derate factor aging/derate factor 1.2 default (>= 1.0 expected); user-suppliedNFPA 72 / panel worksheet