Acre SPC42 - Calculating the Battery Power Requirements

See the technical data for the specific auxiliary current and the corresponding installation
instruction or data sheet of modules, keypads and expanders for current consumption.
Expander 1 Current (mA) + Expander 2 Current (mA) + ….. <Auxiliary Power
If the electronic or relay outputs are already powering external devices, the power supplied to these
devices must be subtracted from the 12V DC auxiliary power supply to determine the amount of
available power from the auxiliary power terminals (0V 12V).
If the total maximum current draw from the expanders exceeds the auxiliary power, a PSU expander
should be used to provide additional power.
Powering expanders from the auxiliary power terminals
1 SPC controller
2 Battery
3 Auxiliary 12V power terminals
4 Keypad
5 Keypad
6 I/O expander
21.4 Calculating the battery power requirements
It is important that adequate stand-by power is available to supply all devices in the event of a mains
supply failure. To ensure that enough power is available, always connect the appropriate back-up
battery and PSU.
The approximations below assume that the SPC controller PCB is drawing its maximum load (all
wired inputs have their EOL resistors fitted) and that the usable output power from the battery is 85%
of its maximum capacity.
0.85 x battery size (Ah) – (Icont + Ibell) = Imax
Time (hours)
Battery size=capacity, in Ah, depending upon SPC housing chosen
Time=backup time, in hours, depending upon security grade
Icont=quiescent current (in A) for the SPC controller
Ibell=quiescent current (in A) for the attached external and internal bells
Imax=the maximum current that can be drawn from the auxiliary power output
Only sealed cell valve regulated battery types to be used.
For EN compliance the supplied current needs to be supported by the battery for required stand
by time.
SPC42/52/53/63 – Installation & Configuration Manual Appendix
© Vanderbilt 2023 266 I-200572
08.12.2023