Fire Alarm Battery Size Calculator

With a standby load of , an alarm load of

and a standby period of hours with 30 minutes in alarm condition,

you will need batteries.

Actual value returned by calculation :

Whoa there tiger... That calculation returned a calculation of ?

You must have entered the Quiescent & Alarm loads in wrong.

Please try again. Remember, the figures need to be entered in milliamps.

If you have entered the figures correctly then please speak with the manufacturers of the equipment because a seperate power supply will probably be needed.

Enter Quiescent Load (mA) :
Enter Alarm Load (mA) :
Standby Period (hrs):
Actual Batteries Installed:

Fire Alarm Batery Size Calculator

This BS5839:1 Battery Capacity Calculator will determine the correct battery capacity required by using the formula given in appendix D of BS5839:1. This calculator assumes an alarm period of 30 minutes as stated in BS5839:1.

Please note that is calculator is for fire alarm systems and can be used with fire panels, EN54 power supply units and all other ancillary fire alarm equipment with 2 x 12v standby batteries wired in series.

To use this battery size calculator simply enter the Quiescent Load value in milliamps, the Alarm Load value in milliamps and the standby period required. 1/2 Amp = 500ma. 1amp = 1000ma.

If you know which batteries have been supplied, you can enter the battery size into the bottom box.

Once you have entered this information, click the 'Calculate' button and the battery capacity required will be shown. If you have entered a battery size then this will tell you if this calculation has passed or not.

Example Battery Formula & Calculation Completed 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

Creating A Pdf

This page offers you the option to download this calculation in Pdf format which details the calculation completed by this calculation.

To create this Pdf simply follow the instructions once you have completed the calculation. You can enter your site details if required.

If you leave the site details form empty then the Pdf will be created with blank fields to allow you to hand write this information in.

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Things To Keep In Mind When Using This Calculator

This calculator is currently only for fire alarm equipment.

Do not install batteries larger than that allowed by the equipment manufacturers. Fire alarm batteries should fully recharge within 24. If you install batteries larger than the manufactueres recommendations then you will not acheive the battery recharge time. This in itself is a non-compliance to BS5839.

This fire alarm battery size calculator is meant to help your process; nothing more. This calculator is supplied 'As Is' and Fase Ltd can not be held responsibe for any incorrect calculations returned by this tool or for any user input. The use of this tool is at your own risk.

Like our calculator or have a question? Please leave us a comment below.

Fire and Security Engineers

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