60 THE DIRECT-CURRENT MOTOR CH. IV 



CHAPTER IV 



SHUNT-WOUND MOTORS 



IN this chapter we shall assume that the magnets are 

 excited by a shunt winding entirely independent of 

 the armature circuit. We have already seen that the speed 

 is given by the equation 



When 7i', If and E are constant, the speed is less than 

 the maximum by an amount depending on the load. 



Example 20. A motor with an induction factor of 

 5 and internal resistance - 2 ohm is connected to a line 

 having a tension of 120 volts. With no load the speed is 

 1,140 revolutions per minute. With a torque of 850 inch- 

 pounds the speed is less than the maximum by 290 

 revolutions. 



The term R in the equation for the speed includes all 

 resistance in the circuit, not only the internal resistance 

 of the motor, but also any resistance that may be in series 

 with it, as, for instance, a rheostat used for the purpose 

 of starting or regulating, E being measured outside such 

 resistance. 



Example 21. If #=120, J/ = 5. If = 0-2. the maxi- 

 mum possible speed is 1,140 r.p.m. If the load is 845 



