8 Battery calculations
This section contains instructions and tables for calculating battery size.
8.1 Current draw for system components
Each component of the FACU has a specified alarm and standby current rating. To calculate the current draw for the system, add the
specified standby current for each module and device to obtain an alarm and a standby current rating for your system.
Note:
1. Include the auxiliary power from the system’s AUX 24 V taps in the calculation, unless that power is switched off during battery
standby. For example, you do not need to include door holders that are operated from 24 V if they are disconnected through a
relay during a battery standby condition.
2. You need to include the notification appliance load in the alarm current total.
The current specifications for each module are described in Table 13.
Table 13: Current specifications for each module
Module Standby current Alarm current
Main system board
(4 Class-B IDCs, 20 detectors each)
100 mA + 9 mA
For each zone in standby
150 mA + 60 mA
For each zone in alarm
Remote LED annunciator 24 mA 26 mA
City connect module 30 mA 60 mA
Use the following steps to calculate minimum Ah battery capacity
1. Total Standby Current (A) =
2. Total Alarm Current (B) =
3. Identify Standby Time (C), in hours (typically 24 hr) =
4. Identify Alarm Time (D), in minutes (typically 5 min) =
5. Using the values in Steps 1 to 4, perform an Initial Battery Calculation using the following formula:
(A x C) + (0.0167 x B x D) = _______ Ah (Ah = ampere hours)
Note: The total current rating for the unit's power consumption, considering the panel board, NAC circuit, and Aux. 24 V load
must be less than 2.2 A.
6. You need to apply a discharge factor (DF) if either the standby current or the alarm current is greater than the C/20 current for
the initial battery size selected. For example, 1 A load on a 10 Ah battery requires a discharge factor of 1.08 (10 Ah / 1 A gives
discharge time of 10 hours; DF = 1.08). Use Table 14 to determine the discharge factor (use the 20 hr value for 24 hr standby):
Table 14: Discharge factor
Discharge time Discharge
factor
Discharge
time
Discharge
factor
Discharge
time
Discharge
factor
Discharge
time
Discharge
factor
0.083 hr 5 min 3.85 2 hr 1.43 8 hr 1.10 14 hr 1.03
0.166 hr 10 min 2.78 3 hr 1.30 9 hr 1.09 16 hr 1.02
0.249 hr 15 min 2.27 4 hr 1.22 10 hr 1.08 18 hr 1.01
0.332 hr 20 min 2.08 5 hr 1.18 11 hr 1.06 20 hr 1.00
0.5 hr 30 min 1.96 6 hr 1.14 12 hr 1.05 48 hr 1.00
1 hr 60 min 1.67 7 hr 1.11 13 hr 1.04 60 hr 1.00
7. Standby Discharge Factor (SDF) = _________ Alarm Discharge Factor (ADF) = _________
8. Minimum Required Battery Capacity Calculation (to account for battery aging, a 1.25 multiplier is included).
Minimum battery capacity in Ah = 1.25 x [(A x C x SDF) + (0.0167 x B x D x ADF)] = _______
9. If the battery size initially selected is smaller than the result of the previous step, repeat the calculations using a larger battery
size.
page 36 579-1402 Rev B
2004 Foundation Series Fire Alarm Control Unit Installation Guide
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