Power Supply Calculations
136 MS-5UD/MS-10UD Series PN 52626:B 8/01/2008
7.4 Calculating the Battery Size
Use Table 7-4 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 control panel under the loss of AC
power. Complete Table 7-4 as follows:
1. Enter the totals from Table 7-3 on page 135, 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 cabi-
net door
7.4.1 NFPA Battery Requirements
NFPA 72 Local, Central and Proprietary Fire Alarm Systems require 24 hours of standby power
followed by 5 minutes in alarm
7.4.2 Selecting and Locating Batteries
Select batteries that meet or exceed the total ampere hours calculated in Table 7-4 . The control
panel can charge batteries in the 7 AH to 26 AH range. The control panel cabinet is capable of
housing batteries up to 18 AH. Batteries larger than 18 AH require the BB-26, BB-55 or other UL
listed external battery cabinet.
For Canadian applications, the minimum battery size is 12 AH and the maximum battery size is
18AH.
TABLE 7-4:Total Secondary Power Requirements at 24 VDC
Secondary Standby Load
(total from Table 7-3 Calculation
Column 3)
[ ]
Required Standby Time
(24 hours)
X[ ] = AH
Secondary Alarm Load
(total from Table 7-3 Calculation
Column 2)
[ ]
Required Alarm Time
(for 5 min., enter 0.084,
for 10 min., enter 0.168)
X[ ]
= AH
Sum of Standby and Alarm Ampere Hours = AH
Multiply by the Derating Factor X 1.2
Battery Size, Total Ampere Hours Required = AH
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