Electric Motor choices - rethinking AC induction motors

[TEG]

Thanks for the replies.

Mini-E uses ACP drivetrain which is an evolution of the EV1 drivetrain.
Apparently Tesla started out by licensing and improving on tech from ACP, so there is a common DNA in all those induction motor EVs.

Yes, it is curious that almost everyone else is using PM if induction has real benefits.

 

[vfx]

My thanks as well for excellent responses. So, "Is Tesla doing it all wrong or is everyone else making the mistake?"

(working on my tabloid headlines today)

 

[jkirkebo]

My thanks as well for excellent responses. So, "Is Tesla doing it all wrong or is everyone else making the mistake?"

Well, I can say that in the train business, AC induction has a MUCH larger market share than PM motors. These motors are larger, usually in the 400-1000kW size. This might indicate that induction motors has an edge in 200+kW motors while PM is probably easier and cheaper to implement in small sizes, like in hybrids and small EVs ?

 

[qwk]

AC induction motors are also MUCH lighter than PM motors.

Tesla is doing things right by using an induction motor.

 

[jkirkebo]

AC induction motors are also MUCH lighter than PM motors.

Tesla is doing things right by using an induction motor.

Weight will also matter more with size. It might not matter much if a small motor for a hybrid weighs 15 or 30kg, but a difference between 50 and 100kg for a larger EV motor is significant.

 

[Eberhard]

Most important is how much is the peak-power compared to the continuos power. because the agility of a car is more depending on that. As better this is, as more dynamic the car will appear. The result: very quick acceleration when to pass a car or go around the corner while haveing very low consumption when driven on highway-speed.

 

[William13]

I believe that Elon has it right. Lighter, quicker, and higher torque. No rare earth metals. Price is likely higher currently but high volume could make the price go down. Elon put a rocket up. I trust his engineering judgement way over that of major auto manufacturers.

 

[JRP3]

Since PM's can lose their "M" if they get too hot I think AC induction can operate at higher temperatures which should mean higher peak power to weight. Motor horse power is all about transferring pack power to the wheels without melting or breaking. AC induction should be cheaper to build as well since they don't use expensive rare earth magnets.

 

[Eberhard]

JB Straubel told me, that the AC-Motor used in Model-S will spin max. 16.000 rpm. Therefor the AC-Motor can be lighter and provide more torque be using a higher fix-ratio gearbox and more amps on the direct coupled PEM with at least 1000A.
This will result in at least 50% more torque at the wheel compared to the standard roadster. You only can do that with AC-Motors. PM Motors would be very heavy and the possible advantage in efficiency is little and will be compensated be the additional weight.

 

[Talkredius]

I think it is a little more complicate :
The main reason for high spinning motors is to save space and weight . The higher the speed of the motor the lesser the space and weight of the motor.
But both motor types, PM + AC could be designed for this . I know a KERS -System ( Formula 1 ) where a PM with 20.000 rpm was used.
With a PM Motor it's not so easy to design the rotor, you need special bandage for the magnets, for the AC Motor it is quite difficult to produce the copper rotor cost efficiently. My employer had had a hard time in 2003 to develop the tools for the cost efficient production of copper rotors for high efficiency AC motors.
The PM motor has nearly no electric losses in the rotor, this is quite different with an AC motor, there for the AC motor is always bigger then a comparable PM motor.
But the main disadvantage for PM motors are the rare earth material you need for the magnets. 90 % of the known resources are in China.

 

[Talkredius]

Since PM's can lose their "M" if they get too hot I think AC induction can operate at higher temperatures which should mean higher peak power to weight. Motor horse power is all about transferring pack power to the wheels without melting or breaking. AC induction should be cheaper to build as well since they don't use expensive rare earth magnets.

In practice ( motors for industrial usage ) this could happen in some cases if "M" was made of Samarium Cobalt, with Neodymium-Iron-Boron , which is commonly used now, I never saw this.

AC motors have to operate with higher temperatures due to the losses in the rotor. PM motors doesn't have such losses (in the rotor).

 

[JRP3]

This guy overheated his neomags and killed them http://www.diyelectriccar.com/forums/showpost.php?p=231731&postcount=191

 

[vfx]

...
But the main disadvantage for PM motors are the rare earth material you need for the magnets. 90 % of the known resources are in China.

While I'm not advocating using RE metals, this statement is flawed. There is a lot of rare earth out there. (ironically) The Chinese have simply undercut the world RE prices because they don't spend on things like safety and the environment. Check what was the largest mine in California: California mine to compete with China in rare-earth metals | California Watch
They bored a hole in the bottom of this mine as deep as they could go and never saw the supply stop.

 

[JRP3]

Some hybrid car companies are working to develop an electric motor that does not use rare earth metals, as California Watch previously reported.

I guess they don't realize that Tesla, (both the inventor and the company), has already done so.

 

[vfx]

For E.V.s and Hybrids, a Free-Spinning Alternative to Rare Earths - NYTimes.com

We are covered by the comments.

 

[vfx]

http://www.sae.org/mags/AEI/9916

Frequent discharges eventually can leave the entire bearing race riddled with pits known as frosting. In a phenomenon called fluting, the operational frequency of the inverter causes concentrated pitting at regular intervals along the bearing race wall, forming washboard-like ridges that result in noise and vibration.

 

[TEG]

Remy EV motor reduces dependence on foreign rare earth metals

 

[VolkerP]

...reduces dependence on foreign rare earth metals

"reduce dependence" reads out, avoiding it at all by going from PM motors to AC motors with an improved stator design.
Kinda "reducing dependence on gasoline" by going pure electric :wink:

 

[dpeilow]

Chinese Rare Earth Company Strokes Mustache, Cuts Off Worlds Access to Rare Earths to Inflate Prices | Popular Science

 

[TEG]

From:
My Nissan Leaf Forum View topic - Leaf to be produced in USA

...Toyota recently signed up a deal with a Canadian mineral exploration company that has found a deposit of rare earth metals that are exactly what Toyota needs for super efficient motor magnets. Toyota is to fund the entire capital cost of the mine infrastructure and take off the production. Avalon Rare Metals - Home
...