Basic concepts, Energy, Motors

How DC motors work?

In this post I will explain how the DC motors work. This is a basic concepts post it will be important to understand future posts.


A wire conducting electrical current in the presence of a magnetic field receive a force. The force’s direction depends on the current’s direction.

Also depends on the direction of the magnetic field. The force’s intensity depends on the angle between the vectors of field and speed of electrons and the intensity of current and magnetic field.

Magnetic force’s equation.

F_{m}=BI\Delta l \cdot sen\theta

B is the magnetic field in tesla (T), I is the current and \Delta l is the conductor’s part. The magnetic force follow the left hand’s rule.

A spire in a magnetic field receive a torque.

DC motor

This is the stator with permanent magnets.

The stator provides a magnetic field, some motors have electromagnets in the stator instead of a permanent magnet.

This is the rotor, the part which rotate, the nucleus serve to increase magnetic permeability, improving the iteration with the flux.

The stator and rotor together.

This highlighted part is the commutator which will make sure the motor keep rotating, without it the motor wouldn’t give a complete turn.

The commutator will stay linked with the brushes (highlighted with red ellipses) which will bring current to the coils. If the rotor’s motor had only one coil in one direction, when it is perpendicular to the magnetic field the torque will be zero. Because of that motors always have more than one coil. With the commutator, the brushes switch the coil side ensuring the rotation.

In a 3 pole DC motor like the one that I showed, a wire can make 3 poles and have 3 plates in the commutator. Turning the motor, the rotor’s winding become electromagnets due to the electric current, the flux’s direction induced by the current is explained by the right hand’s rule. Each pole become an electromagnet which interact with the stator’s magnets.



About Pedro Ney Stroski

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