How much current does a 30 volt 1/2 horsepower motor that is 85 percent efficient draw from the bus?

How much current does a 30 volt 1/2 horsepower motor that is 85 percent efficient draw from the bus?

• A. 12.3 amperes
• B. 9.8 amperes
• C. 16.2 amperes
• D. 14.6 amperes

Answer: (D)

The current drawn from the bus comes from the electrical input power, which is related to the mechanical output and the efficiency. Convert the motor’s shaft power to watts: 0.5 hp × 746 W/hp ≈ 373 W. Since the motor is 85% efficient, the electrical input power is 373 W ÷ 0.85 ≈ 439 W. With a supply of 30 V, the current is I = P/V ≈ 439 W ÷ 30 V ≈ 14.6 A. So, the motor draws about 14.6 amperes from the bus.

The current drawn from the bus comes from the electrical input power, which is related to the mechanical output and the efficiency. Convert the motor’s shaft power to watts: 0.5 hp × 746 W/hp ≈ 373 W. Since the motor is 85% efficient, the electrical input power is 373 W ÷ 0.85 ≈ 439 W. With a supply of 30 V, the current is I = P/V ≈ 439 W ÷ 30 V ≈ 14.6 A. So, the motor draws about 14.6 amperes from the bus.