The DL on DC: Why DC Motors Were Dissed, but Then Became Heroes When They Went Brushless

29.11.17 01:22 PM Comment(s) By Cratos

The history of the DC motor and its modern role in electric vehicles and battery-powered equipment

Cue the violin music. It’s the dramatic moment when our protagonist is pushed back into the spotlight as a hero after being shunned for an imperfection. In this case, it’s the DC motor, which refers to “any of a class of rotary electrical machines that converts direct current electrical energy into mechanical energy.”

This technology was invented with a necessary Achilles Heel, which ultimately caused it lose favor. But along came a new way of thinking about an old problem, and that Achilles Heel was eliminated. Today, DC motors are the darlings that power some of the most admired and desired electric vehicles.

The necessary nuisance

When they were first introduced in the late 1800s, DC motors had brushes. They were necessary to keep the electromagnet’s poles charged in the armature (“the power-producing component”) so it would spin. The brushes are responsible for the change in polarity, and they make physical contact with the two spinning electrodes attached to the armature. Magnetic polarity flips as the electromagnet spins.

The problem with a DC motor with brushes is that those brushes eventually wear out. The entire design places the electromagnet at the center, which makes it harder to cool. The physical contact required by the brushes limit the maximum speed of the motor—not to mention that all this making and breaking of physical contact creates wear, noise, and sparks.

The DC motor with brushes may have been inexpensive to produce, but its heat, noise, and maintenance factors ultimately caused it to lose favor—especially as early electric-powered cars lost out to those with internal combustion engines for about a century.

The DC motor pivot point

Fast-forward to the advent of transistors in the late 1940s. They did more than shrink the size of radios. Transistors and ultimately, computers, made it possible to re-think the design of the DC motor. If you could get rid of those pesky brushes, you’d eliminate practically everything that made them undesirable.

They also became more powerful, as the brushes caused power loss. Getting rid of them would make the DC motor far more efficient while creating a dramatic increase in torque.

So, getting rid of the brushes in DC motors would give them higher output, a smaller size, higher speed, and better heat dissipation, along with a quiet operation.

Outside the box thinking

Transistors were applied to the design of the DC motor to turn it inside-out so the brushes could be eliminated. The permanent magnets were transferred to the rotor, and the electromagnets were moved to the stator, which is the stationary part of a rotary system. Transistors—and today, computers—were brought in to charge the electromagnets as the motor’s shaft turned.

With the brushes eliminated and control given to a computer, the DC motor became far more precise in speed, as well as more efficient. Gone were the noise and sparks, which meant the motor operated cooler and quieter.

The only downside is that they’re more expensive to manufacture.

A return to center stage

The benefits of a brushless DC motor make it perfect for use today. They can be greatly reduced in size to fit in laptop computer hard drives, and even battery-operated power tools.

At the opposite end of the spectrum, they’ve also become the preferred solution for electric vehicles, as well as battery-powered construction equipment. Power, torque, and precision are called for here, and the brushless DC motor delivers them.

You’ll still see brushed DC motors around, though. They cost less to make, so manufacturers factor in the lifespan of a product to determine usage. It’s why you’ll find them in motorized toys and home appliances.

So, the DC motor – now brushless – is back on top again and revolutionizing vehicles and equipment. All it took was a century or so.

At Triple E, we're passionate about keeping pace with an evolving construction industry. For more information on the benefits of battery-powered construction equipment, you can call us at (954)-978-3440 or reach us through our contact form.

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