How Do Electric Motors Work?

Electromagnetism: The Foundation

An electric motor relies on the discovery by Hans Christian Ørsted in 1820: electric current creates a magnetic field around it. The reverse is also true — a changing magnetic field induces electric current (Faraday's law). This interplay between electricity and magnetism is the heart of every motor and generator.

The Lorentz Force: What Drives Rotation

When current flows through a conductor inside a magnetic field, a force called the Lorentz force acts on it:

F = q × v × B × sin(θ)

This force is perpendicular to both the current and the magnetic field — creating rotational motion.

DC Motors

Classic DC motors consist of:

• Stator: permanent magnet or wound coil creating a fixed magnetic field
• Rotor (Armature): wound coils carrying current, pushed by Lorentz force
• Commutator: copper segments that reverse current every half turn, keeping rotation continuous
• Brushes: carbon contacts feeding current to the spinning rotor

Brushes wear out over time. Modern Brushless DC (BLDC) motors use electronics instead, giving longer life and higher efficiency.

AC Induction Motor

Invented by Nikola Tesla in 1888. The most common industrial motor today — no mechanical contact between rotor and stator.

The stator is fed with 3-phase AC current through coils arranged 120° apart. This creates a rotating magnetic field that spins at the supply frequency (50 Hz = 3000 RPM for a 2-pole motor).

The rotor (a "squirrel cage" of aluminum or copper bars) has currents induced in it by the rotating field. These induced currents create their own magnetic field that chases the stator field — and the rotor turns.

Synchronous speed: N = (120 × f) / P, where f = frequency, P = number of poles.

The rotor always runs slightly slower than the field — this "slip" (2-8%) is what induces the current that drives it.

Variable Frequency Drive (VFD)

By changing the frequency of current fed to an AC motor, we control its speed. VFDs save up to 50% energy in pumps and fans, enable smooth starting, and allow precise speed control.

Motor Types Summary

Summary

An electric motor converts electrical energy to mechanical energy through the interaction of magnetic fields and electric current. Understanding this principle guides correct motor selection and effective maintenance.