Rohm Breadcrumb


Magnetic Force
<How Does a Motor Work?>

Motor Rotation Using a Magnet/Magnetic Force

The basic operating principle of a motor is as follows.

Around a permanent magnet having a rotational axis:

① When the outer magnets rotate (referred to as a rotating magnetic field),② The N and S poles attract and repel each other, ③ Causing the magnet with the rotational axis (center) to turn.

Basic Operating Principle of a Motor  

Alternatively, supplying current to a conductor generates a magnetic field around, creating a magnetic force (Rotational magnetic field). This results in the same effect as rotating a magnet.

Here magnetic field is generated by passing a current through a conductive wire

If we wind a conductive wire into a coil the magnetic force is combined, generating a large magnetic flux along with North and South poles.

The magnetic force can be further strengthened by utilizing an iron core to increase magnetic flux density

Actual Motor Operation

Here we see an actual method used for rotating a motor by generating a rotational magnetic field from a 3-phase AC source and conductive coils (3-phase AC is an AC signal with phases shifted 120°).

Current Change (Change in Magnetic Field Strength)
  • The synthetic magnetic field in ① above is shown in ① below
  • The synthetic magnetic field in ② above is shown in ② below
  • The synthetic magnetic field in ③ above is shown in ③ below
Results from the above diagram

As mentioned above, the 3 phase coils (U, V, and W) are wrapped around an iron core, positioned 120° apart, with the higher voltage generated at the North pole(N) and the lower voltage at the South pole(S). Since each phase varies sinusoidally, the pole (N/S) generated from each coil will continue to change, along with the magnetic field.

If we look at just the North pole phase, it switches in order from the U coil → V coil → W coil → U coil, enabling rotation.

Overview of Motors and Motor Driving