Operation Manual

ATMOSPHERIC TEMPERATURE & HUMIDITY POWER LOSSES

These losses are generally considered to be nominal with values seldom exceeding 5%. Natural

atmospheric variations, however, can combine causing nearly 20% de-rating. For example, air of 120°F

(50°C) at 100% humidity. Even 100°F (40°C) temperature at 90% to 100% humidity will cause a 10%

de-rating. The local and/or field operating conditions must be evaluated and the power de-rated from

SAE J-1349 per these factors.

ACCESSORY POWER REQUIREMENTS

Additional power deductions should be made for any accessories that are installed. These deductions are

necessary to accurately identify the expected net power available for the prime power requirement. The

accessory items are variable for each installation / application, and can’t be determined or deducted by

the engine manufacturer. The following accessories are typical in a Stand-By Generator application.

Auxiliary Alternator / Generator End

Engine Alternator

Drive Belts and Pulleys

Cooling Fan

TEMPERATURE RELATIVE HUMIDITY

°C °F 30% 40% 50% 60% 70% 80% 90% 100%

25 77 1.000 .997 .992 .990 .984 .980 .977 .973

30 86 .985 .980 .973 .969 .964 .957 .954 .949

35 95 .966 .960 .953 .947 .940 .934 .928 .920

40 104 .948 .940 .931 .924 .915 .907 .899 .892

45 113 .928 .919 .907 .897 .886 .878 .867 .855

50 122 .910 .895 .882 .869 .854 .841 .830 .815

ATMOSPHERIC FACTORS CHART

POWER AVAILABLE DUE TO TEMPERATURE AND HUMIDITY VARIATIONS