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AMPS-24 Manual —
P/N 51907:J2 02/26/2014
Power Supply Calculations
Calculating the Battery Requirements
4.2 Calculating the Battery Requirements
4.2.1 Calculating the Battery Capacity
Use this table to determine the battery capacity needed for the system:
The following notes apply to Table 4.4:
1. NFPA 72 Local, Proprietary, Central Station, Auxiliary and Remote systems requires 24 hours
of standby power followed by 5 minutes in alarm.
2. Older NFPA standards and certain jurisdictions require 60 hours or standby power followed by
5 minutes in alarm. Verify this requirement with the AHJ.
3. Batteries installed in a system powered by an automatic starting engine generator need to
provide at least 4 hours of standby power.
4. Factory Mutual requires 90 hours of standby for deluge-preaction systems.
5. Emergency voice/alarm communications systems require 2 hours of operation in the alarm
condition. Due to the sporadic nature of voice operation, however, NFPA 72 permits 15
minutes of operation at a maximum connected load to equal 2 hours of normal use.
6. If the total exceeds 200 AH, an Uninterruptable Power Supply with sufficient amp-hour
capacity is needed. The Uninterruptable Power Supply must be UL-listed for Fire-Protective
Signaling.
7. The following battery derating factors must be used for Canadian installations using an
AMPS-24 charger:
• For 7 AH capacity, use derating factor of 1.1
• For 12 AH capacity, use derating factor of 1.2
• For 26 AH capacity, use derating factor of 1.2
• For 55 AH capacity, use derating factor of 1.8
• For 100 – 200 AH capacity, use derating factor of 2.5
Current (amps)
X
Time (hours)
=
_________AH
Secondary Non-Fire
Alarm Current (from
Table 4.2)
________________
X
Required Secondary Non-Fire Alarm
Standby Time (24 or 60 hours)
________________
=
_________AH
Secondary Fire Alarm
Load (from Table 4.2)
________________
X
Required Fire Alarm Standby Time:
*
________________
=
_________AH
Sum Column for Total Secondary Amp Hours calculated
=
_________AH
Multiply by the derating factor x 1.2 (See Note 7)
=
_________AH
Battery Size – Total Secondary Amp Hours Required
=
__________AH
* Following are decimal conversions for standard numbers of minutes:
5 minutes
10 minutes
15 minutes
30 minutes
60 minutes
120 minutes
0.084
0.167
0.250
0.5
1.0
2.0
Table 4.4 Secondary Power Standby and Fire Alarm Load
