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LST700 SERIES INSTALLATION & MAINTENANCE MANUAL • Approved Document No. DFU7002012 Rev 4
LST700 SERIES FIRE ALARM PANEL
Stand-by battery calculation guide
The standby time of the fire alarm panel after the mains has failed depends on the quiescent
loading of the panel, the alarm load of the panel, and the capacity of the batteries.
To determine the capacity of batteries required for any given stand-by period, the following formula
should be used:-
Standby Time in Ahr = 1.25 x ((TxA) + H x (P+Z))
The multiplier 1.25 is present to account for lost capacity over the life of the batteries.
H = Number of hours standby required
P = The quiescent current of the Panel = 0.025A
This figure is with the Mains failed, beeper operative and the Power Supply and General Fault indicators
lit. If there are other quiescent drains on the Panel then these must be added in.
Z = The total quiescent current of all zone devices
As a guideline, the quiescent current of most modern detectors is typically 0.00005A (50
µ
A), and
that of manual call points is zero. To obtain accurate figures consult the device manufacturers’ own
specifications.
A = The total alarm current of the sounders
(plus any other devices connected to other alarm outputs).
T = The amount of time in hours required for the alarm
(most commonly being half an hour).
Example 1:
The panel has 70 detectors each consuming 50
µ
A each, 20 Sounders at 20mA each, the required
standby time is 24 Hours, and the required alarm time is 0.5 Hours.
Z = 70 x 0.00005 = 0.0035A
P = 0.025A
A = 20 x 0.02 = 0.4A
H = 24
T = 0.5
Standby Time in Ahr = 1.25 x ((0.5 x 0.4) + 24 x (0.025 + 0.0035)) = 1.1AHr
Therefore, batteries with at least 1.1Ahr capacity are required.
Example 2:
The panel has 100 detectors each consuming 50
µ
A each, 40 Sounders at 20mA each, the
required standby time is 72 Hours, and the required alarm time is 0.5 Hours.
Z= 100 x 0.00005 = 0.005A
P = 0.025A
A = 40 x 0.02 = 0.8A
H = 24
T = 0.5
Standby Time in Ahr = 1.25 x ((0.5 x 0.8) + 72 x (0.025 + 0.005)) = 3.2AHr
Therefore, batteries with at least 3.2Ahr capacity are required.
APPENDIX
