For the wide variety of DC motor applications, there are those where a straight shunt motor is preferred and others which seem to require the greater starting torque of a series field. Why are there different field designs and are they interchangeable? What about the nameplates marked “stab shunt” or “str shunt?” The purpose of this article is to clear up lingering confusion about the types of fields as well as the benefits of each.
Para la amplia variedad de aplicaciones de motores de CC, existen aquellas en las que se prefiere un motor shunt directo (straight shunt) y otras que parece que necesitan el mayor torque de arranque de un campo serie. ¿Por qué existen diferentes diseños de campo y son intercambiables? ¿Qué sucede con las placas de datos marcadas como “stab shunt” o “str shunt?” El propósito de este artículo es aclarar la confusión permanente sobre los tipos de campos, como también los beneficios de cada uno.
When rewinding field coils, there are a couple of common problems that make life difficult for the service center. One problem occurs when the newly rewound set of shunt fields is returned to the service center, roasted again. What causes this, and whether we can improve our winding procedure, has been the subject of much discussion. We all realize that something caused that first failure. If the subsequent failure looks a lot like it - the shunt fields were charred in both cases then it seems logical that the underlying cause could be the same. Sometimes it is. Let's look at why the coil is burnt. Well sure, it got too hot. But why? Is it because the shunts are energized when the machine is otherwise shut down? If so, the fields can be automatically de-energized after "x" minutes of machine inactivity. Installing a timed relay in the controls will avoid future problems. It may be that the customer is able to trace the problem to a new operator, who needs more training.