20A
YOUR ANSWER: 77.7 percent
Correct. We had an input of 960 watts and an output of one horsepower. We were told
that one horsepower is equal to 746 watts; our problem looks like this:
Efficiency = output x 100 =746
input
960 x 100 = .777 x 100 = 77.7 percent.
The balance of power, 22.3 percent, is lost as heat or friction.
Heat and Friction Losses
22.3 percent of power
Delivered
Power
746 w.
77.7
percent
(output)
In the figure above are pictured the power and the power losses. If you follow the
arrows through this picture, you will find the input power is electrical power. It splits up in the
motor, going in two directions. The losses in the form of heat are radiated upward, and the
output in the form of mechanical power is delivered to the shaft.
Now consider this problem. We have a 5-horsepower motor that draws 20 amperes
from a 200-volt circuit; what is the efficiency of this motor?
93.25 percent.
frame 22A
107.23 percent
frame 24A
1-21
IT0348
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