ELECTRIC MOTOR BASICS
Electric motors are everywhere around us, whirring away according to principles discovered almost two centuries ago. Yet for most of us their inner workings are a mystery. Wheels readers able to discuss the finer points of the internal combustion engine in all its complex variety will likely have only the faintest understanding, if any, of how an electric motor converts current into kilowatts.
This is how it’s done. Create a magnetic field, put a conductor like a copper wire in that field, then connect the conductor to a source of electricity. Result? The magnetism pushes on the wire. This core concept applies to all electric motors, and grasping it is the equivalent of understanding that burning fuel mixed with air in a closed space creates pressure.
Compared to the typical combustion engine’s cylinders, pistons, connecting rods, cranks, valves and cams, an electric motor is elegant simplicity. Arrange magnets around the periphery of a cylindrical casing, set a bunch of conductors lengthways into a cylinder free to rotate inside that casing, and organise some way to supply them with current, and you’ve got an electric motor. The stationary section is called the armature or stator, the rotating part is called the rotor. So far, so easy...
There are many types of electric motors, named according to the way their magnetic fields are created, how the rotor conductors are supplied with current and, finally, what kind of electricity they’re made to consume. These details are the source of the baffling terms you’ll see in almost any description of an electric motor.
One big and basic division is whether the motor uses DC (direct current) or AC (alternating current). Motor magnets can be permanent (typically using the rare-earth element Neodymium), electromagnets (copper wire wound around an iron core and needing electricity to produce magnetism), or hybrid combinations of both. Current can be supplied to the rotor by wear-prone brushes or without a physical connection via electric induction, the same effect that enables inductive charging of batteries in everything from toothbrushes to EVS.
The three-phase AC induction motor has become the dominant type in EVS. It’s the kind of motor that gets electrical engineers very excited. “Judged in terms of fitness for purpose coupled with simplicity, the induction motor must rank alongside the screw thread as one of mankind’s best inventions,” is the way one expert describes it in print.
It’s easy to understand the enthusiasm. These motors convert electricity into driving force with great efficiency. From 85 to beyond 95 percent is the typical range, which makes the 40 percent efficiency of the best automotive combustion engines look downright wasteful.