Monarch SE 2004-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Section 8 Electrical System | 297
If 120 Volt AC is present at the distribution panel L1 and L2 inputs the system
will assume that 120 Volt AC, 30 Amp shore power is available and the energy
management feature will be enabled. If only 20 Amp service is available the user
must select the 20 AMP service mode by momentarily pressing the 20/30 Amp
select switch on the Control Panel. Initially, all relay contacts are closed and the
total current is monitored. If the total current should exceed the service limit the
system will turn off the first load in the shedding table, turning the loads off and
calculating the amount of current that was removed, which is the value for that
load. This value is placed in memory. If the current remains above the service
limit, the system will turn off the next load in the shedding table, again calculating
the amount of current that was removed and placing this value, which is the value
of that load, in memory. The system continues to turn off loads until the total
current falls below shore power amperage or all of the six controlled loads have
been shed. Through this process the system has “learned” the amount of current
that each particular load draws. This feature compensates for the differences in
current draw over a range of line voltage and ambient temperature, by re-learning
the load each time it is turned off or “shed.”
The 50 Amp Smart EMS now waits until the total current is lower than the
service limit and enough current is available (as compared with the amount in
memory for the last load shed) before turning that load back on. This assures that
there is sufficient current to operate the load.
NOTE: There is a two minute minimum delay period after a
load is shed before the load will be turned on again to prevent
air conditioners from turning on with a head pressure.
Three Hour Averaging: The RVIA (Recreational Vehicle Industry Association)
in conjunction with the NEC (National Electrical Council) have established rules
regarding the rating of electrical systems and the use of energy management
systems. One of these rules requires that, if any energy management system is
used, the average total load current for the system over a 3 hour period be limited
to 80% of the service rating. For that reason the 50 Amp EMS calculates the
average running current for the system and, if it exceeds 80% of the service rating,
the EMS sheds loads to reduce the average current below that limit.
For example, if a system operating under 120 Volt AC, 30 Amp service has
been running at the 30 Amp limit for three hours, the EMS will change its
shedding threshold to 24 Amps and turn off loads until the 24 Amp limit is
attained. If the user selects the 20 Amp service mode this limit will translate to
16 Amps. Because the EMS calculates a running 3 hour average, if the average
load current drops below the limit the system will restore power to loads based on
their impact on the limit. If the system is in the averaging mode the decimal point
at the lower right corner of the load meter display on the display panel will illuminate.
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