INSTALLATION & MAINTENANCE MANUAL • Approved Document No. DFU7004010 Rev 3 • Page 23 of 24
LPCB APPROVED CFP 2/4/8 ZONE FIRE ALARM PANEL
STANDBY 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.
Note: LPCB approved systems must use 3.2Ah batteries (YUCEL Y3.2-12).
To determine the capacity of batteries required for any given standby period, the following formula
should be used:
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, internal sounder active and the Power Supply and General Fault
lights lit. If there are other quiescent drains on the panel then these must be included.
Z = The total quiescent current of all zone devices
As a guideline, the quiescent current of most modern detectors is typically 0.00005A (50µA), 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 50µA 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 Ah = 1.25 x [(0.5 x 0.4) + 24 x (0.025 + 0.0035)] = 1.1Ah.
Therefore, batteries with at least 1.1Ah capacity are required.
Example 2:
The panel has 100 detectors each consuming 50µA 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 = 72
T = 0.5
Standby Time in Ah = 1.25 x [(0.5 x 0.8) + 72 x (0.025 + 0.005)] = 3.2Ah
Therefore, batteries with at least 3.2Ah capacity are required.
Standby Time in Ah = 1.25 x [(TxA) + H x (P+Z)]
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