Which Electric Motor Powers Your Electric Car?
What powers an electric car? I know, I know it’s not really a very in-depth question at face value.
And if you said an electric motor, you’d get a big tick on your homework from me.
If you said an electric motor, which in turn gets its power from a battery pack or hydrogen fuel cell stack, then you’d be getting a gold star or two and maybe five minutes of extra time at recess.
Do they still do that anymore? But don’t Pat yourself on the back just yet, because, there are many, many different types of internal combustion engines in use today. There are different types of electric motors in use across the auto industry.
And beyond some are built for power, some are built for speed and others are built for efficiency.
Sometimes you’ll see motors built from a combination of the above.
So today we’re going to take a little look at some of the electric vehicles on the road and figure out just what type of motor powers them.
If you’re interested in the basics of how a motor works, why they’re better than an internal combustion engine for powering cars, and some of the differences between the various motor types, then head on over to this article: Why Electric Motors Are Just Better.
Before we go heads deep on this topic, I just want to touch on the whole AC DC thing.
The majority of electric vehicles on the market use alternating current or AC motors in which a special controller calculates just the right amount of alternating current to send to the motor’s coils to keep the whole thing – that is moving at the right speed and the right direction.
But it wasn’t always the case because math is hard and while fixed speed alternating current electric motors, have been around for years and years, and AC motor design makes for a lower cost, lower maintenance motor.
Compared to a similarly powered DC, building a variable speed alternating current motor is pretty darn hard to do, and only really practical in today’s modern age of integrated circuits and computerized controllers.
This is because computers are good at math. Go back 120 years to the first generation of electric cars, you’d see series wound DC motors in use.
They were good for delivering a high amount of torque from a standstill and got up to speed pretty briskly. However, because the torque of a DC motor is proportional to the speed of the motor.
There’s a pretty noticeable drop-off in power as the motor spins faster, which means your 1910 Baker Electric may not climb that hill as quickly as it sped along the flat, but don’t that means DC motors are rubbish and should never be used.
No, the oldest electric vehicle in existence uses DC motors because of their simplicity and fantastic torque.
No, I am not talking about Elon Musk’s personal Tesla Roadster, I’m of course talking about the lunar roving vehicle that was left on the moon by Apollo 15, the moon buggy, as it is now known.
It uses 4 DC motors, one in each wheel to get it around the challenging Luna terrain. Sure. It wasn’t fast, but it and its two siblings also parked on the moon did seem to get the job done.
If you were in the UK, sometime around the turn of the last century, you may have noticed a large number of GE with electric cars, roaming the streets of London built in India by a company that was eventually acquired by Hendra early gee-whiz cars, which were built for efficiency and low-cost.
They used DC electric motors at first but then switched to AC motors when motor controller technology got to the point where it was more cost-effective.
Remember AC motors are generally better than DC.
The majority of automakers on the market use some form of a permanent magnet, synchronous motor for their electric vehicles.
And I say the majority because while each manufacturer may have a slightly different name for it, they all generally make use of the same basic design and principles.
Why permanent magnet motors, while lighter and more efficient overall, do have some downsides, namely the fact that they rely on rare earth metals to function.
You’ll note that I use the term “some” form because not all permanent magnet synchronous motors are the same.
Some automakers, including Chevrolet, use what’s called an interior permanent magnet synchronous motor.
They put the rare earth metals that form the electromagnetic field that interacts with the motors coil in the rotor.
This not only makes it easier to build, but it means there’s less chance of the motor self-destructing.
And it also means that you can do neat and crazy things with the motor windings like use square wire.
No, I am not kidding you. The Chevy bolt EVs motor uses square wire and its windings, which allows more wire to be packed into a given space, increasing the motor’s power while decreasing its overall physical size.
BMW Doesn’t exactly use a bog-standard permanent magnet motor, either it uses something it calls a hybrid motor, which uses permanent magnets in its design, like a permanent magnet motor, but it’s also built to take advantage of the inductance effect of a reluctance motor.
It effectively takes the best bits from both motor designs and manages to pump out a much higher power output than your bog-standard permanent magnet motor for the same physical size, which of course brings us to Tesla.
While most of the rest of the auto industry, we’re focusing on a permanent magnet electric motor, Tesla chose to use an AC induction motor instead.
It’s kind of fitting really since you know, the father of the induction motor being called Tesla, the person that the company was named after.
The original Tesla Roadster, the Tesla Model S, and the Tesla Model X are all designed to make use of an AC induction motor using a three-phase four-pole design.
They were capable of great versatility and the lack of permanent magnets in those motors was a bonus for Tesla as a startup, as it didn’t have to worry about paying eye-watering high prices for rare earth magnets, which kept its build cost slow.
The most commonly made motors are larger and not quite as energy-efficient as some other designs, despite being able to rotate at crazy high speeds and offering really impressive talk at startup.
That’s what gives the model S its acceleration, which brings us to model three and its permanent magnet synchronous reluctance motor, which to be honest, sounds a lot like the motor that BMW uses in its synchronous reluctance motor.
There are electromagnets around the motors stator, the bit that stays still, and the rotor itself is made of a non-magnetic material interspersed with veins of magnetic materials, which means that the rotor will turn to a preferred orientation.
When there’s a magnetic field applied by switching the status electromagnets on and off, it’s more efficient than the AC induction motor.
And it’s also the cheapest type of AC motor to make, which is a bonus when you’re trying to make a mass-market affordable EV.
But it’s also not so good at high power acceleration from a standstill because it doesn’t produce as much torque as some of the other motor types at lower RPMs.
This is why Tesla has gone the hybrid route for its Model 3 dual motor and more recently the Model X and the Model S these all-wheel-drive Tesla variants have two different types of motors, one for each axle, allowing the cars to have blistering performance.
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Morten has been working with technology, IoT and electronics for over a decade. His passion for technology is reflected into this blog to give you relevant and correct information.Read more...