1. What is the Battery Capacity Calculation?

The battery capacity calculation determines the required battery size for fire alarm systems according to NFPA 72 standards. It accounts for both standby and alarm current draws over a 24-hour period with a 25% safety factor.

2. How Does the Calculator Work?

The calculator uses the following equation:

Where:

• Standby Current — Normal operating current in amps
• 24 — Hours in standby mode
• Alarm Current — Current draw during alarm in amps
• 0.083 — Hours in alarm mode (5 minutes)
• 1.25 — 25% safety factor

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

3. Importance of Battery Calculation

Details: Proper battery sizing ensures fire alarm systems remain operational during power outages for code-required durations (typically 24 hours standby plus 5 minutes alarm).

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: Why is there a 25% safety factor?
A: The 1.25 multiplier accounts for battery aging, temperature effects, and provides a margin of safety as required by NFPA 72.

Q2: What's the 0.083 hour factor?
A: This represents 5 minutes (0.083 hours) which is the NFPA requirement for alarm duration during power failure.

Q3: How do I measure standby and alarm currents?
A: Standby current is measured with system in normal operation. Alarm current is measured with all alarm devices activated.

Q4: Does this calculation work for all fire alarm systems?
A: This is for standard systems. Special systems (voice evacuation, etc.) may require additional calculations.

Q5: What battery type should I use?
A: Sealed lead-acid batteries are most common, but consult manufacturer specifications for your specific fire alarm control panel.