The process of conversion of alternating current into unidirectional current is made with help of a mechanical device called commutator which is attached tho the shaft of the machine and the armature coils.The most common of this is the split ring commutator.The figure below shows a split ring commutator.Look at the first figure.

In the first figure the commutators ie the split ring commutators are attached to the armature coils and during the first half of its rotation in the clockwise direction the coil attached to the split ring ‘A’ acquires positive voltage and that of ‘B’ negative voltage and its taken or tapped outside with corresponding brushes.

The next figure shows the second stage or the rotation after 180 degree during the rotation the coil attached to the split ring ‘A’ get negatively charged and that of ‘ B’ get positively charged but at the same time the position of the split ring also changes and as a result the brushes will have the voltage in the same direction or say they have the same polarity as before and gets a unidirectional voltage with pulses.

In practical the to get high voltage not a single coil is used and we will get a very a pulsating unidirectional voltage with large magnitude.

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