UM1M820BNA User Instructions
Issue AH, March 4, 2013 Spec No. 1M820BNA (Model M820B)
Spec No. 1M820DNA (Model M820D)
8 Chapter 1. Introduction
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Battery LVD (Low Voltage Disconnect)
To prevent serious damage to the batteries during a commercial AC power failure, the batteries can be
disconnected by voltage or time control.
The batteries are reconnected automatically when commercial AC power is restored and a predetermined
DC voltage level is reached.
Voltage Controlled Disconnection: When the set voltage level is reached, the batteries are
disconnected.
Time Controlled Disconnection: When the set time has elapsed, the batteries are disconnected.
Battery Capacity Prediction
The ACU+ can predict battery capacity.
Battery Block and Battery Midpoint Monitoring
The ACU+ can monitor battery blocks (12V blocks) or midpoint battery voltage of battery strings
connected to the EIB assembly. An alarm is issued when either battery block voltage or battery midpoint
voltage is abnormal.
Enhanced Battery Monitoring with SM-BRC
When connected to an SM-BRC, the ACU+ provides enhanced battery monitoring.
Thermal Runaway Detection and Management
Functional Description: The system uses several control mechanisms to avoid thermal runaway.
First: During a short high rate discharge, the batteries will normally get hot. The ACU+ takes this into
consideration. After completion of the discharge duty, the batteries are recharged with a limited current to
avoid heating the batteries any further.
Second: The temperature of the batteries can be monitored, and the ACU+ sets the charge voltage
appropriately, as previously described under Battery Charge Temperature Compensation.
Third: In addition to battery temperature compensation, if battery temperature rises above a set
temperature limit, the system stops battery charging completely by lowering the output voltage to the
“BTRM Voltage” setting. This allows the batteries to cool down. The system also provides alarm
notification of this occurrence. Power supplied to customer equipment is not interrupted.
Fourth: The battery LVD circuits can be programmed to open (disconnect) if a high temperature event
occurs (HTD – High Temperature Disconnect). The contactor(s) open when battery temperature rises
above a programmable value and close again when battery temperature falls below another
programmable value.
With Energy Optimization Mode (ECO):
The Controller monitors load current versus system capacity.
The Controller commands some rectifiers to standby in rotation.
Refer to “1.3.1 Rectifier Control” for further description.