Battery Calculator Fire Alarm System

Battery Capacity Equation:

\[ \text{Battery Capacity (Ah)} = (\text{Standby A} \times 24 + \text{Alarm A} \times 0.083) \times 1.25 \]

Battery Capacity (Ah):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Battery Capacity Calculation?

The battery capacity calculation determines the required ampere-hour (Ah) rating for fire alarm system batteries based on standby current draw and alarm current draw. This ensures the system will operate properly during both normal and emergency conditions.

2. How Does the Calculator Work?

The calculator uses the battery capacity equation:

\[ \text{Battery Capacity (Ah)} = (\text{Standby A} \times 24 + \text{Alarm A} \times 0.083) \times 1.25 \]

Where:

\( \text{Standby A} \) — Standby current in amps
\( \text{Alarm A} \) — Alarm current in amps
24 — Hours of standby operation required
0.083 — 5 minutes converted to hours (0.0833)
1.25 — Safety factor (25% additional capacity)

Explanation: The equation calculates total energy needed for 24 hours of standby plus 5 minutes of alarm, then adds a 25% safety margin.

3. Importance of Proper Battery Sizing

Details: Correct battery sizing is critical for fire alarm system reliability. Undersized batteries may fail during power outages, while oversized batteries increase cost unnecessarily.

4. Using the Calculator

Tips: Enter standby current in amps (normal operation current) and alarm current in amps (current during alarm condition). Both values must be zero or positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is there a 1.25 multiplier?
A: The 1.25 multiplier (25% safety factor) accounts for battery aging, temperature effects, and manufacturing variations.

Q2: What's the 0.083 factor for?
A: 0.083 represents 5 minutes converted to hours (5/60), as NFPA requires batteries to support alarm operation for at least 5 minutes.

Q3: How do I measure standby and alarm current?
A: Use a clamp meter to measure current in standby mode and during alarm activation (with all notification appliances operating).

Q4: Does this account for temperature effects?
A: No, for installations in extreme temperatures, additional derating factors may be needed beyond the 25% safety margin.

Q5: What battery type is this calculation for?
A: This calculation is typically for sealed lead-acid (SLA) batteries commonly used in fire alarm systems.