[Inside the EV Heart] Part 4: Spinning Without Magnets? The Physical Mysteries of the AC Induction Motor (ACIM)
Welcome back to our Inside the EV Heart series! In our previous article, we witnessed the almost "control freak" precision of stepper and servo motors. But if we shift our focus back to "providing massive power," you will discover a mind-blowing fact: some motors out there don't even have a single magnet inside!
How is that possible? How do you create attractive and repulsive forces without magnets? Today, we are going to decode this romantic miracle of physics: the Alternating Current Induction Motor (ACIM).
The "Faraday Magic" That Needs No Real Magnets
The construction of an AC induction motor is arguably the purest and most robust design in the industrial world. It is mainly divided into two parts:
- Stator: The outer ring packed with copper coils, used to feed alternating current (AC).
- Rotor: Inside, there are no permanent magnets and no complex wire windings. Instead, there is a metal cylinder that looks exactly like a hamster wheel, which engineers call a "Squirrel Cage Rotor." It is usually welded together from aluminum or copper bars.
Its operating principle perfectly demonstrates the 19th-century physicist Michael Faraday's "Law of Electromagnetic Induction." When we run AC power into the outer stator coils, these coils generate an invisible, continuously rotating magnetic field.
At this moment, the stationary metal "squirrel cage" in the middle senses the rapid changes in the external magnetic field, and a powerful current is "induced" inside the metal bars. This newly generated current, in turn, creates the squirrel cage's very own magnetic field. When these two magnetic fields interact, the squirrel cage gets "dragged along" by the rotating magnetic field on the outside!
The "Slip" of a Chase That Never Ends
Here is a super fascinating piece of physics trivia: the rotor of an induction motor can never catch up to the speed of the outer rotating magnetic field!
Why? Because if the rotor spins exactly as fast as the outer magnetic field, there is no longer any "relative motion" between them. Without relative motion, the squirrel cage stops sensing the changing magnetic field, the induced current vanishes, and the driving force disappears. Therefore, the rotor must always be just a little bit slower than the rotating magnetic field. This speed difference is known in engineering as "Slip." It is a romantic pursuit where the target can never be caught.
Built Tough, But Prone to "Fever"
The biggest advantage of an induction motor is that it is incredibly rugged and cheap. Since it lacks expensive and fragile rare-earth permanent magnets, it doesn't fear high-temperature demagnetization. Its structure is so simple it's practically indestructible, making it the true "big brother" of the industrial world. The early Tesla Model S actually made its name relying on induction motors (the name Tesla itself is a tribute to Nikola Tesla, the father of alternating current).
But it also has a fatal flaw: rotor heating (copper loss). Because the rotor is forced to generate an induced current, the electricity surging through the metal bars produces a massive amount of waste heat. As a result, when driving at low speeds or stuck in traffic, the energy conversion efficiency of an induction motor falls far behind that of motors with physical magnets.
2026 EV Trivia: It Has Become the Ultimate "Invisible Assist"
Since the induction motor isn't the pinnacle of efficiency, has it been phased out in the EVs of 2026? Not at all! Instead, it has found the perfect strategic position!
In modern high-end dual-motor AWD electric vehicles, engineers usually place an induction motor on the front axle as an auxiliary power unit. Why? Because when you are cruising on the highway at a steady speed and only need a gentle push from the rear wheels, the front motor can be completely "de-energized."
Since there are no physical magnets inside an induction motor, the moment power is cut, the magnetic field disappears instantly. The wheels can coast entirely free from any magnetic drag (zero-drag coasting), which is incredibly energy-efficient! This is a special power that motors packed with strong permanent magnets absolutely cannot pull off.
While the induction motor is fantastic, the quest for ultimate range and instantaneous explosive power means the primary drive in modern EVs is handed over to another breed of monsters—the ones that "bring their own magnets." Moreover, engineers have even changed the shape of the motor entirely, flattening it out like a pancake!
Stay tuned for the next article: [The Ultimate Weapon of Modern EVs] Permanent Magnet Synchronous Motors (PMSM) and the Dimensional Strike of "Axial Flux"!
