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Appendix A: Power Supply Calculations
Calculations must be done to determine standby and alarm DC current loads. Ampere-hour
requirements must be calculated as well to determine battery size.
The on-board power supply provides filtered 24VDC power that may be used for operating external
devices. Use Table A.2 to determine if external loading is within the capabilities of the power
supply.
A.1 Calculating AC Branch Circuit Current
Use Table A.1 below to determine the total amount of current, in AC amperes, that a 120 VAC, 50/
60 Hz service must be able to supply to the fire alarm system. Devices rated for 240 VAC operation
will draw approximately one-half the current listed in Table A.1.
Device Type
Main Power Supply
AA-30
AA-120
ACPS-2406
APS-6R
CHG-120
Sum column for AC Branch Current required=amps
* Separate calculations are required for any devices powered by the
ACPS-2406. It has its own integral battery charger and batteries can be
connected directly to it. Refer to the ACPS-2406 Installation Manual for its
battery calculations.
AC Branch Circuit Installation
For guidelines on wiring the AC branch circuit current, see "Operating Power: AC Branch Circuit"
on page 79 in Appendix B.1 "Electrical Specifications".
A.2 Calculating the System Current Draws
The control panel's main power supply must be able to power all internal system devices (and
several types of external devices) continuously during non-fire alarm conditions. Use column 1 in
Table A.2 to calculate the Non-Fire Alarm Load on the power supply regulator when applying
primary power. The main power supply must also provide a finite amount of additional current
during a fire alarm condition. Use column 2 in Table A.2 to calculate the additional current needed
during fire alarms. The requirements for non-fire alarm and fire alarm current loads cannot exceed
the capabilities of the power supply as listed below:
•
3 A at 24 VDC during Standby; and
•
6 A at 24 VDC during Alarm.
How to Use the Calculating Tables
As used in this section, "Primary" refers to the control panel's on-board power supply, its primary
source of AC power. "Secondary" refers to the control panel's backup batteries (or any other 24
VDC power supply listed for Fire Protective Signaling and connected in place of the batteries). The
term "standby" refers to the output current required when no fire alarm is present. The term "alarm"
refers to the output current required when a fire alarm is present.
The Primary Power Source Non-Alarm Current and Alarm Current columns are DC current
calculations. These calculations confirm that the power supply can provide enough current to
support the system during Primary Non-Fire Alarm and Fire Alarm conditions.
XLS140 Installation Manual Form Number 95-7673-3 P/N 51927:C 12/06/2005
No. of Devices
[ 1 ]
X
[
]
X
[
]
X
[
]
X
[
]
X
[
]
X
Table A.1 120 VAC Fire Alarm Circuit
Current (amps)
Total Current
3.0
=
3.0
1.00
=
1.85
=
*
2.7
=
2.5
=
2.0
=
71
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