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Calculator · Intruder alarm · PD 6662

Intruder alarm battery calculator

Choose the standard and the security grade, then enter the standby current and the alarm current. You get an estimate of the battery capacity needed to run through a mains failure and then sound the alarm, with the working and the next common battery size. It is an estimate, not a compliance check.

Your figures

Insurers and the inspectorates work to PD 6662.

Enter currents in
mA

The whole system on battery, with no alarm.

mA

The whole system in alarm, with the sounder and communicator at full draw.

min

Default 30 minutes.

Advanced
×
D

Result

Enter the standby and alarm currents to see the result.

Working

Ah = ageing × (I1 × T1 + D × I2 × t)

  • I1 is the standby current: everything the battery feeds while the mains is off. Add the panel, keypads, detectors, the external sounder's quiet current and the communicator.
  • I2 is the alarm current: the same total, plus what the sounder and communicator draw when the alarm sounds.
  • T1 is the standby period. t is the alarm period, added on top of the standby period, and is 30 minutes unless you change it.
  • D is the de-rating factor, 1.75 unless you change it under Advanced. It is applied to the alarm current only, because a battery gives less capacity when it is drained quickly.
  • Ageing allows for the battery losing capacity over its life. This page starts at 1.25. Some panel makers use less, for example 85% usable capacity, which is about 1.18.
  • Standby hours: Grades 1 and 2 need 12 hours. Grade 3 needs 24 hours under PD 6662, or 12 hours if mains failure is reported to the monitoring centre. Under BS EN 50131-1 it is 60 hours, or 30 hours if reported.
  • Recharge: the manuals give a maximum of 72 hours for Grades 1 and 2 and 24 hours for Grade 3.

The standby hours are as printed in panel makers' manuals for PD 6662 and BS EN 50131-1, not read from the standards, which are paywalled. Grade 4 is not offered as a preset because sources disagree, so type in the hours from your copy of the standard. The method is the same formula as the fire alarm battery calculator (BS 5839-1, Annex E), used here for intruder alarms too. Check it against your panel maker's figures.

For a fire alarm panel, use the fire alarm battery calculator. It uses the same method, with the fire alarm standby hours. For the grade descriptions, see intruder alarm security grades explained.

For guidance only. Always check against the current edition of the standard and the manufacturer's data.

Built by the engineer behind Kerova, certificate software for fire and security firms.