Carbon Brushes.

[Penguin45]

Many washing machines use a high speed carbon brush motor to turn the drum. These motors are popular due to their compact size, simplicity and the relative ease with which their speed can be controlled electronically. They offer high torque at low speed, as well as very high speed for spinning.

You will notice the considerable difference in size between the motor pulley and the drum pulley. This gives a gearing ratio of (typically) 15:1. This means that at 1000 rpm drum speed, the motor is turning at 15,000rpm. This generates heat!

The carbon brushes are usually mounted in plastic holders attached to the outer casing of the motor and rub against the commutator on the armature (the central revolving part). They are spring-loaded and over a period of time will wear away until motor action becomes erratic or is lost. In the last gasp before giving up, the brushes and holders will become very hot due to arcing and poor contact. Very often, the holders can melt, carbonise or track (develop an earth fault). The latter two problems may not be detectable to the naked eye.

For the above reason, brushes and holders MUST be changed as a pair of complete assemblies. Replacing the brush only can and often does lead to trouble. If the holder goes to ground, you risk blowing the armature, motor safety cut-out, circuit protection fuse and the electronics in any or all combinations. Expensive – you have been warned!

Penguin45.

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