I have a problem regarding DC motors that I am trying to solve. I think that I might not understand the assumptions that are given. The question given is:
A DC series motor is connected to a load. The torque varies as the square of the speed. With the diverter circuit open, the motor takes 20 A and runs at 500 rpm. Determine the motor current and speed when the diverter circuit resistance is made equal to the series field resistance. Neglect saturation and the voltage drops across the series field resistance, as well as the armature resistance.
My solution can be seen here: http://imgur.com/zOaHxfo.
I am not sure if I am simply misinterpreting the given assumptions (bolded above) or if they are nonsensical. For instance, if there is no voltage drop, doesn't that mean that there is no current, and no power is being supplied?
Intuitively, it seems to me that increasing the resistance in parallel with the series field resistance should increase the current and speed while decreasing the back (induced) EMF.
EDIT: It seems the correct answer is given by Bruce Abbott. The speed becomes 1000 rpm and the current becomes 160 A.