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Battery Capacity Equation:
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The battery capacity calculation determines the required ampere-hour (Ah) rating for fire alarm system batteries to ensure proper operation during both standby and alarm conditions, with a 25% safety margin.
The calculator uses the following equation:
Where:
Explanation: The equation calculates total energy requirements for 24 hours of standby plus 5 minutes of alarm, then adds a 25% safety margin.
Details: Proper battery sizing is critical for fire alarm system reliability. Undersized batteries may fail to maintain operation during power outages, while oversized batteries increase cost and space requirements.
Tips: Enter the current draw values in amps for both standby and alarm modes. Values must be non-negative numbers. The calculator will compute the minimum required battery capacity in ampere-hours (Ah).
Q1: Why is there a 25% safety margin?
A: The safety margin accounts for battery aging, temperature effects, and manufacturing variations to ensure reliable operation throughout the battery's service life.
Q2: What if my system requires more than 5 minutes of alarm operation?
A: Adjust the 0.083 factor (5 minutes) to your required alarm duration in hours (e.g., 10 minutes = 0.167 hours).
Q3: Are there battery type considerations?
A: This calculation applies to sealed lead-acid batteries commonly used in fire alarm systems. Other battery types may have different capacity requirements.
Q4: How often should batteries be replaced?
A: Typically every 3-5 years, or as recommended by the manufacturer and local fire codes.
Q5: Does this account for battery temperature derating?
A: No, for installations in extreme temperatures, additional capacity may be needed beyond the 25% margin.