Optima
INSTALLATION MANUAL.
Approved Document No: GLT.MAN-109
PAGE 14
Issue : 1.2 Authorised: GH Date: 31/03/2004
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. Eg 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
= 0.048A
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, so we would recommend using 2Ah
batteries.
