THE DIRECT-CURRENT MOTOR 



OH. 



wound motors in parallel, one of the motors will 

 always be doing some of the work, and cannot be 

 made to generate current however light the load may be. 



Since the motors are mechanically coupled, each will 

 take its own share of the total load. For heavy loads the 

 torque of A will be greater than that of B ; the speeds 

 being the same, the rates of working will be unequal. As 

 the total load diminishes the torques become more nearly 

 equal, until at a certain load they are the same, and for 

 lighter loads the torque of B is greater than that of A. 

 These results are shown in Fig. 24, which gives the differ- 

 ence of current, and hence of electrical horse-power, on a 

 base of total current. 



The difference between the two currents is nothing 

 when the speed is nothing, if, as we have here supposed, 

 the resistances are equal. As the speed increases the 

 difference increases, and, in the case of the motors repre- 

 sented in the drawing, again decreases, but the form of the 

 difference curve will depend upon the shapes of the two 

 induction curves. 



Fig. 25 gives the results of some tests made by 

 Mr. H. S. Hering, on two 25 horse-power railway motors 

 running a car under ordinary conditions. The values 

 observed were as follows : 



If this difference had been due to unequal resistances 

 we should have found the difference increasing with the 



