Instruction manual

ACU-1000 Operations Manual
Interoperability Now 2-7
2.7 DC Power Requirements
The ACU-1000 will operate on +11 to +15 VDC, and the power supplies will automatically
switch over to DC operation if the AC input voltage sags too low. Actual power consumption
will depend on the number of interface modules installed. The DC power input characteristic
of the unit is essentially constant power, i.e., the input power
To find the input current given the input voltage, divide the input power by the voltage:
requirement is constant so the
input current varies with the input voltage and number of modules installed. A fully loaded
chassis consumes 56 Watts when run at a nominal 12V DC.
 56W / 12V = 4.66A at 12V input.
To find the power consumption for less than a fully-loaded unit, use the following formula:
 Power Consumption (W) = 7.5W + (3.85W times number of modules).
2.7.1 DC Voltage Operation
The PSM-1A will automatically switch over to DC operation if AC line voltages drop too low.
The PSM-1A operates with a nominal +12 VDC input only; it does not contain any provisions
for +24 VDC.
CAUTION: Always disconnect both the AC and DC input power cabling
from the ACU-1000 prior to servicing the unit.
NOTE: Any DC power supply connected to the ACU-1000 DC input
must be Safety Extra Low Voltage (SELV) certified.
2.7.2 Battery Power for the ACU-1000
The ACU-1000 may also be connected to a 12V battery to provide back-up power if the AC
mains fail. When powered by a +12V battery at the DC input, the ACU-1000 current
consumption is the following: 0.623A + (0.32A * # interface modules). In other words, the
basic chassis with PSM-1A, CPM-4, and HSP-2A modules draws 0.623 Amps, and each
interface module draws an additional 0.32 Amp. So the current consumption would be shown
as Load Current in Figure 2-3 below. The actual Amp-hours (AH) at a 20 hour rate are also
shown for reference.