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017-882-B0-001 Rev. E (06/2018)
1.0 Introduction, Continued
1.2.2 Standby Operation
When the incoming AC line voltage drops or rises significantly or a complete power outage occurs, the control logic’s line
monitor activates standby operation. During the transfer from AC line to standby operation, the battery powered inverter
comes online as the isolation relay switches to prevent AC power from back-feeding to the utility. The following changes
also occur within the power supply:
• The isolation relay opens to disconnect the AC line from the primary winding of the ferroresonant transformer.
• The control logic switches the inverter FETs on and off. This switching action converts the DC battery current into
AC current in the inverter windings of the ferroresonant transformer, providing regulated power to the load.
• The control logic, which includes a microprocessor and other circuits to protect the inverter FETs from overcurrent
damage, monitors the condition of the batteries and the inverter during standby operation. Since a prolonged AC
line outage could severely discharge the batteries, resulting in permanent damage, the control logic disables the
inverter when the batteries drop to a predetermined cutoff voltage.
• The XM3-HP offers two user-selectable EOD options based on either overall string voltage or individual battery
voltage. See Table 1-1 for battery specific EOD settings. Operation is defined as follows:
• Battery String Voltage Mode which shuts off the inverter when the 36V bus voltage reaches Low Battery
Cutoff Voltage as seen at the inverter.
•
Individual Battery Voltage Mode which shuts off the inverter when any battery in any string (1-4) reaches Low
Battery Cutoff Voltage.
• All units will factory default to Battery String Voltage Mode.
•
Individual battery EOD will only be available (user-selectable) if individual battery voltages are being sensed
and present at logic card via the Smart AlphaGuard, DM3/DSM3/IDH4 or other approved status monitor card
with individual battery voltage sensing.
•
When set to Battery String Voltage Mode the “Low Battery Cutoff” (EOD) is not user adjustable from the
default. See Table 1-1 for more information.
•
When set to individual Battery Voltage Mode the “Low Battery Cutoff” (EOD) will automatically set to default
values based on battery type (see Table 1-1). A secondary option is then offered to the user for manually
programming the “Low Battery Cutoff” (EOD), regardless of battery type, within the range 1.65 to 1.80 V/C.
1.2 Theory of Operation
1.2.1 AC (Line) Operation
During AC Line operation, utility power is routed into the primary winding of the ferroresonant transformer through the contacts
of the transfer isolation relay. Simultaneously, in the inverter, power is directed to the rectifier circuitry providing power for the
control circuitry. The bidirectional inverter also serves as a battery charger during line operation. The ferroresonant transformer
and an AC capacitor form the resonant tank circuit, which provides excellent noise and spike attenuation, output short-circuit
current-limiting, and output voltage regulation. The ferroresonant transformer produces a quasi square wave output which
resembles a rounded square wave.
When measuring the output voltage of ferroresonant transformers, use only a true RMS AC voltmeter. Non-
RMS reading meters are calibrated to respond to pure sine waves and do not provide an accurate reading when
measuring
quasi
square wave output.
NOTICE
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