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Calculating the Battery Size
7 If using Gentex brand NACs, the max number of devices for each NAC output is 35. The "UL Max" current rating, published in their data sheets, must
be used in order to maintain performance under low battery conditions with the maximum wire resistances shown in Table D.2 on page 139.
8 Total Alarm current load cannot exceed 3.0 amps.
9 When AC power is initially applied to the panel and the battery is not fully charged, an initial charge current of up to 5.3 amps may be observed at the
battery. This high current is only applied for a very short duration (milliseconds) and does not affect system load or battery size calculations.
10 Total Standby current load cannot exceed 2.25 amps.
9.4 Calculating the Battery Size
Use Table 9.4 to calculate the total Standby and Alarm load in ampere hours (AH). This total load determines the battery size (in AH),
required to support the system upon loss of primary (AC) power. Complete Table 9.4 as follows:
1.
Enter the totals from Table 9.3 on page 126, Calculation Columns 2 and 3 where shown
2.
Enter the NFPA Standby and Alarm times (refer to 'NFPA Requirements' below)
3.
Calculate the ampere hours for Standby and Alarm, then sum the Standby and Alarm ampere hours
4.
Multiply the sum by the derating factor of 1.2 to calculate the proper battery size (in AH)
5.
Write the ampere hour requirements on the Protected Premises label located inside the cabinet door
Total Standby Load, Battery Powered
(from Table 9.3 Calculation Column 3)
[
Total Fire Alarm Load, Battery Powered
(from Table 9.3 Calculation Column 2)
[
Sum of Standby and Alarm Ampere Hours
Multiply by the Derating Factor
Battery Size, Total Ampere Hours Required
9.4.1 NFPA Battery Requirements
NFPA 72 Local, Proprietary, Central, Auxiliary and Remote Fire Alarm Systems require 24 hours of standby power followed by 5 min-
utes in alarm.
9.4.2 Selecting and Locating Batteries
Select sealed lead acid batteries that meet or exceed the total ampere hours calculated in Table 9.4 . The control panel can charge batter-
ies in the 7 AH to 18 AH range. The control panel cabinet is capable of housing batteries up to 18 AH. Batteries larger than 18 AH
require a UL listed external battery charger and cabinet such as the BB-26, NFS-LBB or other UL listed external battery cabinet.
NFW-50X Manual — P/N LS10129-001NF-E:C 7/25/2018
Required Standby Time
(24 hours)
]
X[
Required Alarm Time
(for 5 min., enter 0.084,
]
for 10 min., enter 0.168)
X[
Table 9.4 Total Secondary Power Requirements at 24 VDC
]
=
]
=
=
X 1.2
=
Power Supply Calculations
AH
AH
AH
AH
127
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