I've seen this video and read this article about commutators but I still couldn't get how commutators reverse the direction of current.I would like an simple and intuitive answer.

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    $\begingroup$ What about e.g the Wikipedia article is unclear to you? $\endgroup$
    – Nephente
    May 3, 2016 at 8:22
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    $\begingroup$ @Nephente:I only could get that the conductor is rotating but I couldn't get how the rotation reverses the current direction since the positive and negative terminals doesn't change at the carbon brushes. $\endgroup$
    – justin
    May 3, 2016 at 8:26
  • $\begingroup$ Commutators are simple mechanical switches that "turn" a circuit element around. If pole A was connected to to $net_A$ and pole B was connected to $net_B$, then the commutator connects A to $n_B$ and B to $n_A$. This can be done synchronously to the rotation of an electrical machine, which turns the AC voltage generated by the coils of that machine into a pulsating DC voltage. $\endgroup$
    – CuriousOne
    May 3, 2016 at 8:29
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    $\begingroup$ @CuriousOne:Oh sorry I couldn't get what you meant by $net{A}$. $\endgroup$
    – justin
    May 3, 2016 at 8:44
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    $\begingroup$ I thought this was a learning forum. I understand the OP's question very clearly and am wondering why so many of you 'closed' the question as unclear. Seriously. On other forums like Quora, this exact question was answered thoroughly and in clear detail. Please let's try to include every learner here. $\endgroup$
    – suse
    May 12, 2019 at 23:49

1 Answer 1


A split-ring commutator is basically a current reversing "tool" used in electric motors. A typical picture of the parts of a motor looks like this:

enter image description here

As you can see the commutator consists of two round copper pieces. A piece of graphite is lightly pushed against the copper to conduct the electricity to conduct to the armature. It's often called a carbon brush. It assures the flow of current to the armature coil. When current reaches armature coil, it develops a magnetic field and tends to align with the external permanent magnetic field. So the coil rotates. This also makes the commutator to spin and each time when the commutator spin, the carbon "brushes" against the copper. As you can see, as the motor rotates, each copper piece connect to the brush on every half turn. But the two copper pieces never touch each other. There is a "split" in between the pieces.

Now let's see how this commutator could reverse the current. We, first have a current coming in from the left. The carbon (graphite) brushes the copper and so this current flows to the armature coil. The armature coil rotates. So the commutator in contact with the armature also rotates. The wire on the left side has the current direction same. So the armature keeps on rotating in the same direction.

enter image description here

Once the coil completes half a turn (just ignore we have a commutator), then the forces on the coil will be opposite. So the coil has a tendency to rotate in the opposite direction. But no need of worry. We have the commutator. Once the coil has done a $180^0$ rotation, the commutator also makes one. Remember that the current through the coil is dependent on the copper piece contact with the carbon. Here the right copper plate appears on the left side which means the part of coil which was initially right (carrying a current downwards) now appears at the left. The copper plate conduct current from the left. So the current in the coil becomes opposite. Thus the forces again reverse which makes the coil to continue it's rotation along a single direction.

So the commutator reverses the current in every half turn producing a steady torque and the armature coil rotates in a single direction.

I explained up to my best. Hope this helps


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