The Figure above shows the speed torque relationship of a permanent-magnet DC mo

Question

The Figure above shows the speed torque relationship of a permanent-magnet DC motor. It is rated at 1/8 hp and 2500 rpm. What is the stall torque of this motor? How fast does this motor run when there is no load attached to the shaft? What is the rated torque of the motor? Do this two ways: (1) from the graph, and (2) from the power and speed rating. The answers should be almost the same. If the load (torque) on the shaft is slightly higher than the rated torque, the motor will run a little slower than 2500 rpm. Will it deliver more power or less power? Find an equation for the power as a function of torque. At which torque does the motor delivers the highest amount of power, and how mu Ch power is delivered (in hp)?

Explanation / Answer

6)

stall torque = 300 oz-in from graph

7)

No load speed= 3000 rpm from graph

8)

a)

rated torque from graph = (0+300)/2

=150 oz-in

9)

less power as power is maximum at rated torque

10)

at 150 oz-in torque the power is maximum

9)

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