Brooks Firetracker FT128 CIE - Current Consumption Calculations; Main Power Source (Power Supply); Standby Power Source (Battery)

Technical / Programming Manual
FT128 Rev 2.2
173
25.2 Current Consumption Calculations
The following calculations should be carried according to the application requirements of
the related current standards, such as AS7240.2, AS1670.1, and AS1670.4.
In order to avoid overloading the power supply, the battery capacity calculation must be
performed as per AS1670.1 clause 3.16.4. The total FT128 current consumption (excluding
battery charging current) has to be calculated.
Note: The batteries will not charge when fire alarm is activated in FT128.
Use the values in chapter "Current Consumption”, page 168, to calculate the total system
current i.e. alarm current I
A
and quiescent current IQ.
As per AS1670.1 Section 3.16.4, the battery capacity requirement shall be determined as
follows:
C
20
= 1.25 [(I
Q
x T
Q
) + FC (I
A
x T
A
)]
Where C
20
= Battery Capacity in AH at 20h discharge rate at 15C - 30C
1.25 = Compensation factor for expected battery deterioration
I
Q
= Total system quiescent current in Ampere
T
Q
= Quiescent standby power source time, normally 24 hours for externally
monitored systems and 72 hours for unmonitored systems
FC = Capacity de-rating factor, typically 2
I
A
= Total system alarm current in Ampere
T
A
= Alarm load standby power source time, normally 0.5 hour
Refer to Brooks spreadsheet to automatically calculate the battery capacity.
Comments regarding I
Q
and I
A
:
 I
Q
has to be ≤ 0.7 A.
 I
A
has to be ≤ 1.8 A.
Note: A "High current" fault (see above) will not be generated in this case since the
battery charging is turned off as long as a fire alarm is activated.
25.3 Main Power Source (Power Supply)
The main power source is a Switching Power Supply which is an AC to DC converter from
230 V
AC
to 24 V
DC
, 1.8 A, i.e. the total current consumption including maximum battery
charging current must not at any time exceed 1.8 A. Input voltage allowed is 176-264
V
AC
. The output voltage is 24 V
DC
with a tolerance of ±1%.
177
25.4 Standby Power Source (Battery)
The standby power source is two 12VDC batteries. Only batteries with a specified "Final
voltage" of 10.5 V must be used.
As per AS1670.1 the required battery back-up time is 24 hours in normal state and 0.5 hour
in alarm state.
177
The output voltage is factory set to 24 VDC. On the power supply is a potentiometer for output voltage adjustment (±10%)
available. Do not use this potentiometer unless the output voltage is not 24 V.