©
2020 Sensata Technologies
Page 35
Operation
3.2.2 Transfer
3.2.2.1
Intelligent AC Input Transfer
When switching from Inverter mode to Standby mode, the MSH3012RV quali
fi
es the incoming AC
voltage and frequency, and synchronizes to the AC source intelligently
1
.
If you connect an AC source with a neutral leg and two hot legs to the MSH3012RV, this power must
come from either a split-phase (120/240VAC) or three-phase (120/208VAC) source. When one of
these AC sources is connected, the inverter
fi
rst quali
fi
es the AC voltage and frequency on the AC2
input. Once the inverter veri
fi
es that the AC2 input is correctly out-of phase with the AC1 input and
after the AC voltage and frequency on the AC1 input has been quali
fi
ed, the inverter synchronizes
and transfers the AC2 input to the AC2 output. After a short delay, the inverter then synchronizes
and transfers the AC1 input to the AC1 output and puts the inverter into Standby mode.
If connecting a 120VAC only source, it must be connected to the AC1 input. Once this incoming
120VAC source has been quali
fi
ed on the AC1 input, the inverter will synchronize and transfer the
AC1 input to both the AC1 and AC2 outputs.
Note
1
:
This inverter is designed to transfer the AC1 and AC2 inputs independently to provide a
delay in switching between them. This delay allows the phase of the inverter output to synchronize
with the phase of the incoming AC source for better transfer to the load.
3.2.2.2
Transfer Time
When in Standby mode, the AC input is continually monitored. Whenever AC power falls below the
VAC dropout voltage (80 VAC, default setting), the inverter automatically disconnects the incoming
AC source and transfers back to Inverter mode with minimum interruption to your appliances—as
long as the inverter is turned on. The transfer from Standby mode to Inverter mode occurs in
approximately 16 milliseconds. While the MSH3012RV is not designed as a computer UPS system,
this transfer time is usually fast enough to hold them up.
The VAC dropout setting can affect the ability of the loads to transfer without resetting. The lower
this setting, the longer the effective transfer will be and therefore, the higher the probability for
the output loads to reset. This occurs because the incoming AC voltage is allowed to fall to a level
that is so low that when the transfer does occur, the voltage on the inverter’s output has already
fallen low enough to reset the loads. The disadvantage of a higher VAC dropout setting is that
smaller generators (or large generators with an unstable output) may nuisance disconnect. This
commonly happens when powering loads that are larger than the generator can handle—causing
the generator’s output voltage to constantly fall below the inverter’s input VAC dropout threshold.
Constant
Current
Reduced
Current
Reduced
Voltage
Absorb
volts
Max
Charge
Rate
Increased
Voltage
Constant
Voltage
Monitored
Voltage
No Current
Monitored
Current
Bulk
Charging
Absorb
Charging
Float
Charging
Full
Charge
Goes to Full
Charge after
4 hours in
Float Charge
Absorb
Time
Float
volts
Time
DC
Voltage
DC
Current
Figure 3-4, Automatic 4-Stage Charging Graph
