Fire alarm battery calculator
Size the standby battery for a fire alarm panel.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Non-alarm load
- 0.2 A
- Maximum alarm load
- 2 A
- Connected to a remote receiving centre
- Yes
- Alarm period, minutes
- 30
- Ageing factor
- 1.25
- Temperature factor
- 1
- Cells in series
- 12
Required capacity at 20 °C
7.25Ah
- Minimum capacity before factors
- 5.8Ah
- Standby period
- 24h
- Standby capacity
- 4.8Ah
- Alarm capacity at the entered period
- 1Ah
- Ageing factor
- 1.25x
- Temperature factor
- 1x
- Capacity from the load and the factors
- 7.25Ah
- Governing figure
- Capacity from the load and the factors
- Charger current to restore in 24 h
- 0.5A
- Float voltage
- 26.4V
- Float voltage tolerance
- ± 0.36V
- Monthly test minimum voltage
- 19.2V
This result is a design aid. Verify it against the current standard.
Calculation steps
- Standby period24hNZS 4512:2010 Cl 213.1
- Standby capacity4.8AhNZS 4512:2010 Cl 213.1
- Alarm period entered, minutes30NZS 4512:2010 Cl 213.1
- Clause alarm period, minutes30NZS 4512:2010 Cl 213.1
- Governing alarm period, minutes30NZS 4512:2010 Cl 213.1
- Alarm capacity at the entered period1AhNZS 4512:2010 Cl 213.1
- Alarm capacity at the governing period1AhNZS 4512:2010 Cl 213.1
- Ageing factor1.25x
- Temperature factor1x
- Capacity from the load and the factors7.25AhNZS 4512:2010 Cl 213.1
- Minimum capacity before factors5.8AhNZS 4512:2010 Cl 213.1
- Required capacity at 20 °C7.25AhNZS 4512:2010 Cl 213.1
- Governing figureCapacity from the load and the factorsNZS 4512:2010 Cl 213.1
- Charger current to restore in 24 h0.5ANZS 4512:2010 Cl 212
- Float voltage26.4VNZS 4512:2010 Cl 212
- Float voltage tolerance0.36VNZS 4512:2010 Cl 212
- Current limit voltage per cell1.85VNZS 4512:2010 Cl 212
- Monthly test duration10sNZS 4512:2010 Cl 602.7
- Monthly test discharge rate, hours5NZS 4512:2010 Cl 602.7
- Minimum service life, years5NZS 4512:2010 Cl 213.5
- Monthly test minimum voltage19.2VNZS 4512:2010 Cl 602.7
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the fire alarm battery tool do?
The tool adds the ampere hours the panel draws during the standby period to the ampere hours it draws during the alarm period. It applies an ageing factor and a temperature factor, and reports the capacity at 20 degrees Celsius.
How long must a fire alarm battery last?
AmpSize uses 24 hours of standby where a monitoring link is present, and 72 hours where none is. It then adds 30 minutes of alarm load. All three figures come from NZS 4512:2010 Clause 213.1. The form option switches between the two standby periods.
Can the result fall below the clause figure?
No. Clause 213.1 and Clause 213.2 give minimum periods. AmpSize works out a minimum capacity before the factors, on the longer of the clause alarm period and the period you enter, and never reports less than that figure. A short alarm period raises a warning instead.
What charger and float voltage does it report?
AmpSize divides the capacity by 24 hours and adds the non-alarm current. That gives the charger current of Clause 212.1. It also multiplies 2.20 V and 0.03 V by your cell count, for the float band of Clause 212.5.
What is the monthly test criterion?
Clause 602.7 tests the battery for 10 seconds at the 5 hour discharge rate or higher. During that test the battery gets no help from another source. Its voltage must not fall below 80 percent of its nominal voltage.