As part of our new website, we have introduced a battery size calculator which will automatically calculate the minimum size of battery required to comply to BS5839, depending on the standby (quiescent), alarm and period figures entered.
The battery standby capacity should be sufficient to maintain the system in an operational condition for at least 24 hours after which there should still be sufficient capacity to provide an "Evacuate" signal in all alarm zones for a minimum of 30 minutes
Please note that this tool is for a 24v DC fire alarm panel or PSU only. This tool will return a wrong calculation for any other voltage range.
To use this tool simply enter your Standby(Quiescent) load and Alarm load readings as milli-amps into the fields, select the required time period then hit 'Calculate'. A new window will appear showing the results of the calculation and the minimum size of battery required.
Example Calculation Performed By This Tool
Assume standby load of 250mA, alarm load of 750mA and a standby period of
24 hours with 30 minutes in alarm condition:
Cmin = 1.25((24 x 0.25) + 1.75(0.75 x 0.5))
= 1.25((6 + 0.66))
= 8.32 aH
From this result, a minimum of 9ah batteries would be required to maintain this system for the required period.