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July, 2017, CTT motor question

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    December 2001
  • From: Austin, TX
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July, 2017, CTT motor question
Posted by lionelsoni on Saturday, May 27, 2017 4:44 PM

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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