On page 18, the answer to a fellow trying to reverse a 1940 model with a universal motor is to swap the brush wires, which will do the job. However, the answer also asserts that the brushes and the field are wired in parallel. I think CTT got this wrong, for two reasons:
o Shunt-wound motors, whether AC or DC, tend to run at a nearly constant speed, very unsuitable for prototype or model trains.
o Shunt-wound AC motors have the further problem that the currents in the field and armature can be substantially out of phase, reducing the torque produced.
In a series-wound motor, the same current flows through the field and through the armature, so there can be no phase difference between the two parts of the motor.
A series-wound motor also works well over a wide speed range. That is why both prototype and model locomotives have traditionally used series-wound motors, whether with DC voltage or, as laminated universal motors, with AC voltage.
Bob Nelson
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