How Electric Motors Work
It can be easy to forget the value of the modern-day electric motor. From the experiments of Benjamin Franklin to later developments with electromagnets, electric motors have developed into the many forms benefiting us daily.
Electromagnets lie at the heart of electric motors. Picture a nail with dozens of loops of wire wrapped around it. Connecting opposite ends of the wire to a battery turns the nail into a magnet, with functioning north and south poles where the battery is connected. If you then surround the nail/electromagnet with a fixed-in-place magnet (like a horseshoe-shaped magnet), the nail begins to turn as the north and south poles of the electromagnet are repelled by the fixed magnet.
The nail, however, will only turn a half rotation before it slows or stops. This is due to the way magnets naturally attract and repel one another. An electric motor must go one step further, so that when this half-turn completes, the field of the electromagnet flips from North-South to South-North, causing the electromagnet to continue another half-turn, completing a full rotation. If the field of the electromagnet were flipped at precisely the right moments at the end of each half-turn of motion, the electric motor will spin.
So, then, an electric motor is a system of wire loops, electrified and repelled by magnets, rotating as long as electricity is applied. The wire loops are called the “armature” and the connection to the power source is the “commutator.” Together, these parts are housed in the axel of the motor. Increases of the amount of armature loops within the motor will lead to a smoother-running motor.
You can figure out the direction in which the wires (armature) will twist using a handy memory aid: Fleming’s “Left-Hand Rule (aka the Motor Rule).”
Extend out the thumb, first finger, and second finger of your left hand. If you point the second finger in the direction of the current (which flows from the positive to the negative terminal of the battery), and the first finger in the direction of the field (which flows from the North to the South pole of the magnet), your thumb will show the direction in which the wire moves.
- First finger = Field
- SeCond finger = Current
- ThuMb = Motion
An electric motor can be smaller than a AA battery, or massive like our 3,700-pound severe duty motor. While the internal builds of these motors may be different, the same core principles apply to all electric motors: commutator, armature and axel.
Outside of the design of a motor, there can be variance in the way electricity gets applied to the commutator: “series-wound” or “shunt-powered configuration.” Series wound motors have good starting torque, but the speed of the motor drops drastically with the load. A shunt motor has a low starting torque, but is able to run at almost a constant speed regardless of the load. Depending on your work application, reliable starting may take priority over consistency of speed.
There are several types of electric motors, too. Large “induction” AC motors (used in large factory machines) work slightly different: they pass alternating current through opposing pairs of magnets to create a rotating magnetic field, and the magnetic field itself causes the motor to spin. Linear motors are laid out into a long continuous track, twisting in a straight line – you’ll find it in such things as factory machines and floating “maglev” (magnetic levitation) railroads.
While electric motors can be simple in their common design, there are many to choose from. Give us a call and we can help you determine the right motor for your needs and your budget!