INFINITY 8 INSTALLATION MANUAL
Approved Document No. GLT-201-7-1
PAGE 15
Issue: 1.6 Author: NRPJ Date: 27/7/2012
10. STANDBY BATTERY CALCULATION
In order to calculate the standby battery size required, the following formula can be used:-
Battery Size (Standby time in Amp Hours) = 1.25 x [(T
ALM
x I
ALM
) + (T
SBY
x (I
QP
+ I
QZ
))]
Where:
T
ALM
= Maximum time in hours required for the alarm [½ hour is most common time]
I
ALM
= Total Alarm Current in amps for all alarm devices connected to the alarm circuits
T
SBY
= Standby time in hours for the system after mains failure [normally 24, 48 or 72 hr]
I
QP
= Quiescent current in amps of control panel in fault condition [because of mains failure]
I
QZ
= Quiescent current in amps of all detection zones. E.g. Ion detector 0.00005 Amp (50 μA) , Optical Detector =
0.0001 Amp (100 μA)
Typical Example:
A system comprises of 20 ionisation detectors, 14 bells and the required standby is 24 hours. It will need to operate in alarm for ½
hour.
Calculate the battery size required.
T
ALM
= 0.5 Hr
I
ALM
= 14 x 0.025 =0.35A [This assumes the bell current is 25 mA. Most alarm Devices show their operating current]
T
SBY
= 24 Hr
I
QP
= 0.085A
I
QZ
= 20 x 0.00005 =0.001A [the quiescent current for an ionisation detector is 50 μA]
Therefore using the equation:
Battery Size (Standby time in Amp Hours) = 1.25 x [(T
ALM
x I
ALM
) + (T
SBY
x (I
QP
+ I
QZ
))]
Battery Size (Standby time in Amp Hours) = 1.25 x [(0.5 x 0.35) + (24 x (0.048 + 0.001))]
Battery Size (Standby time in Amp Hours) = 1.25 x [0.175 + (24 x 0.049)]
Battery Size (Standby time in Amp Hours) = 1.25 x [0.175 + 1.176]
Battery Size (Standby time in Amp Hours) = 1.25 x 1.351
Battery Size (Standby time in Amp Hours) = 1.69 Amp Hours
This system would require a minimum of 1.69Ah batteries.
