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UM1M820BNA User Instructions
Issue AH, March 4, 2013 Spec No. 1M820BNA (Model M820B)
Spec No. 1M820DNA (Model M820D)
74 Chapter 2. Operation
This document is property of Emerson Network Power, Energy Systems, North America, Inc. and contains confidential and proprietary information owned by Emerson Network Power, Energy
Systems, North America, Inc. Any copying, use, or disclosure of it without the written permission of Emerson Network Power, Energy Systems, North America, Inc. is strictly prohibited.
Over Load Operation
If the load current is greater than the combined current capacities of the ACU+ system and the existing
power system, both power systems will go into current limit. Both systems and the batteries will feed the
load. The output voltage will depend on the conditions of the batteries. This operation occurs if the total
capacity of the rectifiers is too low in relation to the need for increased current.
2.7.3 Operating Modes
Figure 5 illustrates the four modes of operation described above.
The Normal Load Operation is considered to be the normal mode. In this mode both the ACU+ system
and the existing parallel power system are both delivering load current. This is main purpose of using
Power Split, to avoid putting the burden of delivering the entire load onto one of the two power systems.
2.7.4 Requirements and Conditions
The two DC power systems must be connected in parallel as described in “2.7.5. Paralleling the Existing
and ACU+ Power Systems”.
Before paralleling the two systems, the following conditions must be met for proper Power Split function.
Note: The control features of the combined system are limited to those of the original power system.
Note: The same type of batteries with an equal amount of cells and the same charging voltages must be
used for both systems.
The float voltage, equalize voltage, and battery test voltage of the ACU+ power system must be set to
the same levels as that of the existing power system.
The remote sense, if available and connected, of both the ACU+ power system and existing power
system must be connected to the same point.
If batteries are used, they must be of the same type.
All the functions specific to the existing power system and ACU+ power system and which depend on
the voltage or which act on the voltage must be disabled from the existing power system and ACU+
power system. This includes the following…
any equalization function,
any temperature compensation function,
any charge control function,
any battery discharge test function, and
any invalid current alarm.
In lieu of this, if battery charging and battery test functions are implemented in the existing power
system, they can remain if signals for starting are connected from the control system of the existing
system to the ACU+ system.