The Washing Machine Man

Appliance Specialist.

Carbon brush motors in appliances....

The purpose of carbon brushes is to provide an electrical circuit to the armature. In technical terms the brushes allow current to flow via the commutator segments to create the magnetic field required to make the motor turn. The mechanical contact between the carbon brushes and the commutator segments must be a positive connection. This is ascertained by springs that press against the back of the brushes and continue to press the brushes against the commutator, even as the brushes wear down. The upper picture shows the brushes making contact with the commutator.The  time it takes to wear out a set of motor brushes does vary, depending upon the load placed on the motor. The harder the drum of the washing machine is made to turn, the faster the brushes wear down. Under normal conditions the brushes will last at least seven years, and even more in a lot of instances. Shorter brush life occurs when loading of a heavier nature than intended is placed on the motor requirement. One common innocent way of overloading the motor is to use too much detergent and create oversudsing and thereby suds lock 

The overloading with clothes is relevant too, but suds lock has a more severe effect on the motor brush life. Symptoms of worn motor brushes include, the machine will wash but not spin, or the motor will not run at all if the brushes collapse altogether. Also if the motor has been overloaded consistently the commutator segments become raised and misshapen, and this causes the motor to run noisy with a somewhat high pitched screeching noise.  Induction motors are used in more expensive machines. These motors do not have any mechanical connection to the armature, but are a bit mote expensive. They are simpler in design but  the electronics to drive them is a bit more sophisticated. See the article on Induction motors.The picture shows a set of carbon brushes

┬ęCopyright Tony Pike 1/1/2011

 

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