Note:
This Battery Backup Calculator is designed to help you estimate the required battery capacity for a fire alarm system based on the standby current, alarm current, standby time, and alarm time. It also includes a safety factor to account for additional capacity needs, ensuring the system operates reliably under all conditions.
Key Inputs:
- Total Standby Current (Amps): The current drawn by all devices in standby mode (e.g., Fire Alarm Control Panel, annunciators).
- Total Alarm Current (Amps): The current drawn by all devices in alarm mode (e.g., horns, strobes, bells).
- Standby Time (Hours): The duration the system must operate in standby mode without primary power (typically 24 hours as per NFPA 72).
- Alarm Time (Hours): The duration the system must operate in alarm mode without primary power (typically 5 minutes or 0.083 hours as per NFPA 72).
- Safety Factor: A multiplier to account for uncertainties, aging of batteries, and additional safety margins (default: 1.2).
Fire Alarm System Secondary Battery -Set Calculation Sheet
How It Works:
The calculator determines the battery capacity required to support the system during both standby and alarm conditions. It calculates the energy needed for standby operation and alarm operation separately, then combines them to provide the total battery capacity. A safety factor is applied to ensure the system remains reliable over time.
Why Use This Calculator?
- Compliance with NFPA 72: Ensures your fire alarm system meets the standby and alarm time requirements.
- Reliability: Accounts for battery aging and unexpected loads by including a safety factor.
- Ease of Use: Simply input the standby and alarm currents, along with the required times, and the calculator will provide the necessary battery capacity.
Important Considerations:
- Battery Aging: Over time, batteries lose their capacity. The safety factor helps account for this degradation.
- Temperature Effects: Battery performance can vary with temperature. Ensure the selected battery can operate effectively in your environment.
- System Load Changes: If you add or remove devices from the system, recalculate the battery capacity to ensure it remains adequate.
By using this calculator, you can ensure your fire alarm system has sufficient battery backup to operate reliably during both standby and alarm conditions, meeting the requirements of NFPA 72 and providing peace of mind.