Bs5839 1 2025 Battery Calculator

Battery Capacity Formula:

\[ \text{Battery Capacity (Ah)} = [(\text{Standby Current (A)} \times 24 \text{ (h)}) + (\text{Alarm Current (A)} \times 0.5 \text{ (h)})] \times 1.25 \]

Required Battery Capacity:

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1. What is the BS 5839-1:2025 Battery Calculation?

The BS 5839-1:2025 standard specifies the requirements for fire detection and fire alarm systems in buildings. The battery capacity calculation ensures the system can operate for 24 hours in standby mode plus 30 minutes in full alarm mode, with a 25% safety margin.

2. How Does the Calculator Work?

The calculator uses the BS 5839-1:2025 formula:

\[ \text{Battery Capacity (Ah)} = [(\text{Standby Current} \times 24) + (\text{Alarm Current} \times 0.5)] \times 1.25 \]

Where:

Standby Current — System current draw during normal operation (amps)
Alarm Current — System current draw during alarm condition (amps)
24 — Required standby duration in hours
0.5 — Required alarm duration in hours (30 minutes)
1.25 — 25% safety margin factor

3. Importance of Proper Battery Sizing

Details: Correct battery sizing is critical to ensure fire alarm systems remain operational during power outages and can activate all alarm devices when needed. Undersized batteries may fail when most needed, while oversized batteries may be unnecessarily expensive.

4. Using the Calculator

Tips: Enter the standby current and alarm current in amps. These values should be obtained from the fire alarm panel specifications or measured values. 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 manufacturing tolerances to ensure reliable operation throughout the battery's service life.

Q2: What if my system has different duration requirements?
A: For systems requiring different standby or alarm durations, adjust the 24 and 0.5 factors in the formula accordingly.

Q3: How often should batteries be replaced?
A: BS 5839-1 recommends battery replacement every 4 years or according to manufacturer's instructions, whichever is shorter.

Q4: Does this calculation include battery recharge time?
A: No, this calculates the minimum capacity needed. Additional capacity may be needed if the system must operate while recharging after frequent power cuts.

Q5: What about temperature effects on battery capacity?
A: Battery capacity decreases in cold temperatures. For installations in unheated areas below 20°C, consider increasing the capacity further.