EFFICIENCY OF A DYNAMO-ELECTRIC MACHINE 195 



Determination of Efficiency from Name-plate Data. The 

 full-load efficiency of a motor can always be approx- 

 imately determined from the rating given on its name plate. 

 The A.I.E.E. rules specify that, among other things, the 

 name plate of a motor shall give the voltage and current 

 for which the machine was designed at full load, and the 

 output in horsepower (if the machine is a motor). 



.100 200 



Current Input 



FIG. 115. Loss Curves and Efficiency Curve for a Motor, 



Suppose, for example, that the rating of a certain 

 machine from the name plate is 110 volts, 38.5 amperes, 

 5 h.p. 



The watts input, full load = 110X38.5 =4350 watts. 



The watts output, full load = 5 X 746 = 3730 watts. 



Hence the full-load efficiency = 3730 -r- 4350 = 85.7%. 



