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 wait 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 it will turn 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 pre-
vent 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 manage-
ment 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 VAC, 30 Amp service has
been running at the 30 Amp limit for three hours, the EMS will change its shed-
ding 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 cur-
rent 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 illumi-
nate.
Display Panel: The display panel is located in
the inside overhead compartment next to the entrance
door and connects to the distribution panel located in
the bedroom. Six power status LEDs indicate power
is applied to those loads. These LEDs are on when
the power is applied. The load meter has a two digit
display to indicate the amount of current actually
being drawn by all the appliances in the motorhome.
Four service type LEDs indicate the source for
120/240 VAC power. Three of these sources are
automatically detected and indicated by the EMS,
namely: Gen Set Service, 50 Amp Service and 30
Amp Service.
Electrical Systems - House
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