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Starter Motor, How they Work (Parts 5) – armature & commutator

Starter Motor, How they Work (Parts 5)
 armature & commutator

 The armature

This sits in a field housing (or body – yoke). There are two types of field housing; one with permanent magnets, the other with field coils which are wound around ‘pole shoes’. These pole shoes only become magnetised when a current flows around them.

Most field coil windings can be replaced - although they are often hard to remove because the pole shoe screws are normally very tight indeed. The permanent magnet version suffers more from un-stuck magnets (which can be stuck back) - but don't turn them round. Broken magnets are normally caused by being tapped with a hammer.

The commutator

Usually at the back of the armature is the commutator. The brushes bear directly on this to transfer the electrical current to and from the armature.