This Huge Electric Dump Truck Never Needs to Plug In

There's an electric dump truck that's all over the internet right now: It's called the eDumper. What's so great about an electric dump truck? Beyond being electric, there are two cool things about it. First, it's huge—HUGE. It has a weight of 45 tons. Second, it doesn't need an external power source to charge the batteries. It charges itself by moving a bunch of rocks down an incline. That is indeed awesome. But how does it work?

Regenerative Braking

One feature of this electric dump truck is it uses is regenerative braking. Actually, many electric vehicles do this. It's a way for the vehicle to recover some energy as it slows down. Here's how it works.

Let's start by considering an electric motor. If you have electric current running through a wire, it creates a magnetic field. Since the electric current makes a magnetic field, it will interact with other magnetic fields—like the one a permanent magnet creates. By forming this wire into a loop, you can get a torque on this current so that it spins. Boom. That's an electric motor. Here, you can build one yourself—it's not too difficult.

Rhett Allain

Rhett Allain

But wait! There's more. If you reverse this process, you can turn this motor into a generator. (A changing magnetic field will create an electric current.) Take a look at this short demonstration. By moving this magnet into a coil of wire, the changing magnetic field makes a current that is measured by this sensitive current meter.

Rhett Allain

Rhett Allain

A rotating coil of wire is perfect in this case because you need a changing magnetic field to generate current. As the coil flips over, the magnetic field through the coil changes—that's exactly what you need. But there you go, an electric motor and an electric generator are the same thing. It just depends on how you use it. If you run current through it, it will turn and you get a motor. If you turn the coil, you get current.

But how do you use this as a brake? Let's put this idea of a generator and an electric motor together at the same time. If you have a spinning coil of wire in a magnetic field, it induces a current. But that induced current also creates a magnetic field. This magnetic field opposes the external magnetic field and makes the coil difficult to turn. So, by turning the motor into a generator it creates resistance and acts like a brake. That's regenerative braking and that's how an electric dump truck charges its battery.

Charging With a Load

Regenerative braking can charge a battery even if you are traveling at a constant speed—however, you have to use the brakes. The is exactly the solution for a vehicle moving down an incline at a constant speed. Really, it's all about energy. Let me start with a diagram of a dump truck moving down a hill at a constant speed.

Rhett Allain