Many service centers are unable to perform full-load testing of large DC machines. The good news is that there are specific tests that can be performed on a DC motor to verify the integrity of windings, the correct relative polarity of armature to interpoles, and proper running performance. This article explains specific tests that can help ensure a motor operates properly when the motor is installed. 

There is now a much-needed DC repair standard, created through the participation of EASA members and industry motor users.

Existe ahora una norma para las reparaciones de CC muy necesaria, creada gracias a la participación de miembros de EASA y usuarios de motores de la industria.

When there is a need for cleaning the contact surfaces of commutators and slip rings with brushes, emery cloth with aluminum oxide is NOT recommended, as conductive abrasive particles will cause arcing and damage to the surface. Many times, stone cleaning, garnet paper and machining are not a convenient, sufficient, or cost-effective option for machines as the priority is to keep the downtime to a minimum. This is when the carbon brush can be designed to clean up the contact surface.

Cuando sea necesario limpiar las superficies de contacto de los colectores y anillos rozantes, NO se recomienda usar tela de esmeril con óxido de aluminio, ya que las partículas abrasivas conductoras pueden causar arcos eléctricos y dañar la superficie. Muchas veces, la limpieza con piedra, el papel granate (Garnett) y el mecanizado no son una opción conveniente, suficiente ni rentable para las máquinas, ya que la prioridad es minimizar el tiempo de parada. En este caso, la escobilla de carbón se puede diseñar para limpiar la superficie de contacto.

This video shows the proper way to lubricate the deep-groove, open ball bearing before assembling a horizontal induction motor.

This video shows the proper procedure for seating carbon brushes in a DC machine.

This video will walk you through how to check the relative polarity of DC machine interpoles and the armature and correct it if necessary using a simple interpole polarity test.

This video demonstrates the correct way to use an induction bearing heater to install an interference fit ball bearing on a machine shaft.

When working with DC machines, it’s not uncommon to find a customer who runs different products requiring a range of armature current. Unlike other conductors, where lower current is a good thing, carbon brushes are designed for a narrow range of current density. A unique aspect of carbon brush life is that brushes operating at a much lower current density than they are designed for do not last nearly as long as expected.