How copper could be key to EVs’ viability

Photo courtesy of the Copper Development Association.

Cutting the price tag on electric vehicles will be key to their widespread adoption.

But the Chinese, who supply 97 percent of the rare earth elements like niobium and samarium that are used to make the powerful permanent magnets that are used in many automotive electric motors (like that in the Toyota Prius) are holding back supply and have raised prices by as much as a factor of four in the past year. China’s move has prompted a search for alternatives.

One that has emerged is what’s known as an AC induction motor. This design, which was used by Chevrolet in its EV-1 electric car in the late 1990s, does away with costly permanent magnets, instead inducing a magnetic field in coils in the spinning rotor through stationary field coils that are located in the motor’s housing. Most of the rotors in AC induction motors are made from cast aluminum but Bob Weed, Vice President of the Copper Development Association, thinks that copper could be a better choice.

“We looked at the AC induction motor. If you replace the aluminum rotor with a copper rotor, which has much better conductivity, you’ll avoid a lot of the losses,” said Weed. “You’ll also avoid the losses of a permanent magnet motor by not having a drag on the motor when it is in a high speed coasting situation,” he added.

The high-priced Tesla Roadster electric sports car uses a hand-fabricated copper and steel rotor to build a motor that weighs just 100 pounds and that can generate 300 horsepower while taking up no more space than a bread box. But building the rotor by hand is expensive, so the key is to develop the same kind of casting technology for copper rotors as is used to make the aluminum versions. The much higher melting point of copper when compared to aluminum makes this difficult, but the CDA has been working with companies in the US, India and China and initial production motors are in production.

Although aluminum is lighter, copper has higher conductance, which means the rotor can be made smaller and thus less expensive while producing a more compact motor with the same power, or can be made the same size, but with 25-30% more power, according to Weed.

“Using a cast copper rotor instead of a fabricated rotor then should be able to get much better performance for much less money.”

4 thoughts on “How copper could be key to EVs’ viability

  1. This is really cool news! Any word on when the technology will be viable and used in “common-man vehicles?”

    Would the copper induction motor result in an electric vehicle that can go further? Because that is what I see as one of the biggest drawbacks to electric vehicles in the USA. Americans are just spread out too far to make electric cars make sense.

  2. My sources at CDA tell me that at least two Chinese companies are already building small motors with copper rotors, and one company in Taiwan is making experimental motors for electric vehicles, so it shouldn’t be long. Electric motors are already pretty efficient (over 80%) so the increase in efficiency with the better conductivity of copper probably isn’t as important as the ability to make the motor smaller with the same power, or more powerful at the same size. Everything else being equal (which it never is) it is battery chemistry and how much battery you have that is going to determine practical range. Still, the copper rotor could be an important piece of the puzzle, especially if China keeps holding back the exports of rare earth elements.

  3. I am amazed how the green community is constantly trolled by headlines announcing new developments that have been common knowledge for decades. Frankly, I’m amazed that permanent magnet motors have been so popular in EV applications. Additionally, you’ll note that the key element to the efficiency gain in an electric motor when compared to an internal combustion engine is the torque curve. To accelerate a mass to given speed there is much force needed to overcome the static inertia. In cars this is where torque comes into play. Note also that once moving, much less torque is required to increase the velocity relative to that very initial push. So, what you want is lots of torque at low speeds. Internal combustion engines produce less torque at low speeds than high speeds. This is why the torque converter is so crucial to the modern vehicle. We have created two linked systems as a band-aid to the poor fit that ICE engines have for moving vehicles – multiple gear ratios and torque converters – both of which provide various degrees of efficiency loss. But back to the point – you want lots of torque at low speeds and ICE’s are reverse of that model. However, electric motors match that need much better. In fact, contrary to your championing of the AC motor, it is not it nor the Permanent magnet motors that are so great, but Brushed Series Wound DC motors. There is no greater source of brute torque. This why cranes and industrial winches have for decades used series wound dc motors. And as a note, they all use copper, copper, and more copper, and have for decades. And don’t even go into the whole maintenance argument against brushes. In an EV application they will need as much attention, though less frequently, as brake pads and can be as easy to change for around the same cost. And yes, it is possible to do regen braking with a properly designed DC motor and accompanying controller.

  4. You are right- each type of electric motor has its strengths and weaknesses. Series wound DC motors are the torque champions at low speed, brushed permanent magnet motors are good at producing torque at higher speeds, but suffer losses when coasting at high speed, AC motors are small and light, produce more heat, but have very little coasting losses… But as you so clearly point out, any one of them is a better technical solution than the torque curve created by an internal combustion engine and yet we’ve managed to work around its limitations for more than 110 years. I doubt that there will be one “winning” electric motor technology as car companies and motor designers keep refining their products.