Specifications

Owners Manual
SILENT RUNNER INVERTER/CHARGER POWER SYSTEM
20
Automatic Power Transfer Switch Theory of Operation
The function of the Automatic Transfer Switch is to automatically accept AC input power from shore or generator,
and use this power to operate inverter loads and to provide power for battery charging. Upon loss of AC input power,
the transfer switch automatically switches the AC loads back to inverter power. Transfer time is approximately 30
milliseconds (0.030 seconds). The 0.030 second transfer time allows all but the most sensitive loads to transfer from
inverter power to shore power and back to inverter power without interruption.
AC input voltage is monitored for proper tolerance at all times. When the AC input is within tolerance for
approximately 5 seconds, the power is passed through to the output circuit and the SR-Series automatically switches
from inverter mode to battery charger mode. The SR-Series automatically switches back to inverter mode when input
power is disconnected or when input power is no longer within tolerance. See SRC12-1100PT Specifications page
for AC input voltage tolerances. The 5 second delay occurs only if the inverter is fully ON when input power
becomes available. There is no 5 second time delay if the inverter is in the ‘Load Demand Mode’ when input power
becomes available.
The factor that determines whether the unit is in ‘inverter mode’ or ‘battery charger mode’ is the presence or absence
of ‘in-tolerance’ input power. Whenever ‘in-tolerance’ input power becomes available the unit automatically switches
from inverter mode to charger mode.
The transfer switch switches both hot and neutral. For safety purposes the inverter output neutral is connected to the
inverter chassis ground only when the unit is in inverter mode. This is a requirement of the National Electric Code for
all systems of this type that neutral should be connected to ground only at the source of AC power, which is the
inverter when in inverter mode. When an external AC input (shore power, generator) is available, the SR-Series
Transfer Switch system breaks the connection between neutral and inverter chassis ground. The neutral-to-ground
connection for passthrough power is then provided by the AC input source.
Figure 1 Battery Charging Graph