Operation Manual

MOTOR LOADS
When figuring generator set capacity requirements for installation involving motor loads, do not
overlook the high current demanded by the motor during start-up. The “In-Rush” of starting current may
be 2 to 5 times higher than that required when the motor reaches normal operating speed. Reserve
capacity must be allowed for in rush demands plus other loads, which could be on the line as the motor
starts.
Air conditioning units are the most common type of motor loads for a generator set in a
recreational vehicle. The starting characteristics of the different makes of air conditioners vary greatly.
For example, a particular 12,000 BTU unit may have lower starting requirements than a 10,000 BTU
unit of another make. When only one unit is involved there is usually no starting problem provided of
course the lighting and appliance load is not too high when unit is started.
The trend seems to be toward larger capacity air conditioners and the use of more than one unit in larger
vehicles. Simultaneously starting two large units can present a problem if the capacity is marginal.
Because of the variation in starting characteristics of the different makes of air conditioners, no definite
statement can be made in this publication regarding multiple-motor starting capabilities.
Delayed starting or use of “easy starting” devices on air conditioner units should be considered
whenever simultaneous starting of more than one motor is involved. The starting and running
requirements of some motor loads common to mobile applications are listed in the table below. Use this
as a guide when selecting generator set capacity requirements involving motor loads. Also note the
Kilowatt De-rating factor for generator set capabilities regarding air conditioners. Capabilities will vary
according to “Kilowatt De-rating”.
BASED ON CODE “G” ELECTRIC MOTOR ELECTRIC MOTOR
HORSEPOWER
STARTING WATTS RUNNING WATTS
½ 2000 1100
1 3800 1800
2 6000 2800
3 8000 4000
4 11000 5500
5 13000 6500
KILOWATT DE-RATING
All units are rated at 1.0 power factor. The Kilowatts of the generator set will decrease 3.5% per
1,000 feet (305m) above 500 feet (152m) above sea level. De-rate 1% for every 10 °F (5.5°C) above
68°F.
ELECTRICAL LOADS
While the electrical load of the vehicle should have been calculated prior to purchase of the generator
set, you may want to recheck the load before installing the set to make sure the capacity is ample to meet
the demands without possible overloading.
The lighting load is usually easiest to calculate in most cases, simply add the wattage of each
lamp to be operated off the generator set. Note that in many applications, not all of the lights or lamps
are in the generator sets AC circuit. Some are DC powered by the 12-volt battery in the vehicle. Make
sure the total includes only lights actually on the generator sets AC circuit. The lighting load is usually
not to heavy in mobile installations however it must be accurately calculated to prevent overloading. For
example, if all lights are on at the same time and the air conditioner or other motor equipment starts up,
this may possibly cause an overload situation.
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