Fire Alarm Battery Calculation Requirements

Battery Capacity Equation:

\[ \text{Battery Ah} = [(\text{Quiescent Current (A)} \times 24 \text{ (h)}) + (\text{Full Alarm Current (A)} \times 0.083 \text{ (h)})] \times 1.25 \]

Required Battery Capacity:

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1. What is Fire Alarm Battery Calculation?

The fire alarm battery calculation determines the minimum battery capacity required to power a fire alarm system for 24 hours in standby mode plus 5 minutes in full alarm, with a 25% safety margin as required by standards.

2. How Does the Calculator Work?

The calculator uses the following equation:

\[ \text{Battery Ah} = [(\text{Quiescent Current} \times 24) + (\text{Full Alarm Current} \times 0.083)] \times 1.25 \]

Where:

Quiescent Current — Standby current draw of the system (amps)
Full Alarm Current — Current draw during alarm condition (amps)
24 — Required standby duration (hours)
0.083 — Required alarm duration (5 minutes in hours)
1.25 — 25% safety margin

Explanation: The equation calculates total energy requirements for both standby and alarm modes, then adds a 25% safety factor as required by fire codes.

3. Importance of Proper Battery Sizing

Details: Proper battery sizing is critical to ensure fire alarm systems remain operational during power outages and can activate all notification appliances during an emergency as required by NFPA 72 and other standards.

4. Using the Calculator

Tips: Enter the system's quiescent current (standby current) and full alarm current (current draw when all devices are activated). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is there a 25% safety margin?
A: The 25% margin accounts for battery aging, temperature effects, and ensures reliable operation throughout the battery's service life.

Q2: What standards require this calculation?
A: NFPA 72 (National Fire Alarm and Signaling Code) and UL standards require this calculation methodology.

Q3: How often should batteries be tested?
A: Monthly visual inspections and annual discharge testing are typically recommended.

Q4: What if my system has multiple power supplies?
A: Each power supply's battery should be calculated separately based on its load.

Q5: Does this account for battery derating?
A: No, additional capacity may be needed for extreme temperatures or specific battery types.