Video: Primer on Tesla Model S Electric Motor

MAR 12 2014 BY MIKE ANTHONY 30

In this video from EdisonTechCenter, they explain in detail how the Tesla Model S operates using its 3-Phase, 4-Pole induction motor.3-phase 4 Pole Induction motor

The motor is roughly the size of a watermelon and, like all electric motors, has 100% torque ready to go at any time with no need to shift gears as the Model S has a 1-speed gear box.

For the Model S, this motor combined with the 1-speed gearbox means that there’s no acceleration lag all the way to the vehicle’s top speed.

Check out the video for more details on the Model S’ electric motor.

 

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30 Comments on "Video: Primer on Tesla Model S Electric Motor"

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Aaron

Ironic that the EDISON Tech Center is highlighting an A/C motor (invented by Nikola Tesla) in a car named the Tesla.

George Bower

This was a good video. It could have been a little more technical though.

Does anyone know what kind of gears are used in the gearbox. Are they Helical / spur gears or is it a planetary reduction???

Mint

I also found the info lacking, and there were a few errors in there. The motor gives you peak torque from 0 rpm to around 5000 rpm, not “any RPM”. After 5000 rpm, you hit peak power at lower torque. Also, the Audi S8 is a bit faster, due to AWD and 520 hp.

I don’t understand why Tesla doesn’t flout the Model S motor weight, like it did with the Roadster.

I can’t find that spec anywhere. They can get free publicity from tech heads.

David Murray

I’ve honestly been at a loss to understand how the motor in the Tesla works. It has no permanent magnets, and no brushes. I don’t get it.

ModernMarvelFan

Are you being serious or sarcastic?

David Murray

I’m being serious. I understand how brushed motors work, and I understand how brushless permanent magnet motors work, such as the one in my Nissan Leaf. I do not understand how a motor can operate without brushes OR permanent magnets.

Scott Franco

“I’m being serious. I understand how brushed motors work, and I understand how brushless permanent magnet motors work, such as the one in my Nissan Leaf. I do not understand how a motor can operate without brushes OR permanent magnets.”

To make a motor, all it takes is to have two mangnets, a rotor and a stator. Either or both of them could be electromagnets. A common example of that is the alternator in a car (generators and motors are basically the same thing). Alternators have no permenent magnets. It relies on the fact that the battery can supply the field coils in the stator.

For the Tesla motor, my understanding is that they use a standing wave AC in the stator, that is to say, instead of poles (and copper wire windings), they feed the stator with AC tuned to provide a standing wave. Basically this means that if you tune the frequency right, you can create positive and negative poles in a conductor. Basically the “wave” stays in one place in the conductor.

This is the real rocket science with the Tesla motor. I was hoping that they would go into that, but they didn’t.

Mint
Let me shed a little light on the subject. Consider a stationary magnetic field running between two magnets (they can be either permanent or DC electromagnets for this thought exercise). If you put a highly conductive loop of metal inside that field, then there is a flux passing through the loop: http://en.wikipedia.org/wiki/Magnetic_flux If that loop rotates, the loop area as seen from the magnets changes, so flux is changing with time, and that induces a voltage around the loop via Faraday’s Law: http://en.wikipedia.org/wiki/Electromagnetic_induction Current is induced, and the energy dissipated comes from the loop’s rotation, so it slows down, and if it’s a really thick loop and a strong magnet, it feels like the loop is moving through syrup. Basically, a torque gets applied in the opposite direction of the loop’s rotation. So now imagine if you have lots of loops to amplify the effect and make it more uniform through the rotation: this is what an induction motor rotor looks like (called a squirrel cage). Steel is put in the gaps of the squirrel cage to help strengthen the magnetic field from an electromagnet: http://en.wikipedia.org/wiki/Permeability_(electromagnetism). So now you have a rotor that moves through a stationary magnetic field like… Read more »
ModernMarvelFan
In a simple way, motors move due to the magnetic fields between the stator and the rotor. In a traditional DC motor with brush, the switching of the magnetic field is handled by the mechanic rotation of the rotor which changes the excitation state of the electro magnet. Your Brushless version basically switch the rotor and stator so the permanent magnet is on the rotor and stator are excited by the electro magnet. As the rotor rotates, the magnetic field in the stator is controlled by the external circuits to switch as needed in replacement of the brush. In an Induction motor. The rotor is excited by an induced current that generates a magnetic field that “follows” the magnetic field in the stator. The stator magentic field “rotates” around (no parts moving) and the rotating magnetic field is causing the rotator to move with it by the induced current in the rotor. In a way, it is similar to the induction stove that you are seeing except the rotor is excited to have a magnetic field. The amount of the slip between the two field is correspond to torque generated. But the more slip you have, the more torque you… Read more »
Bill Howland
David, the posts here are all confusing the issue. The stationary Stator (hence the name), makes a rotating field simply by the action of the applied polyphase voltages (Please don’t ask how that split-phase motor on your drill press, or pedestal sump pump works because the reason for it working is much, much more complicated, having to do with simultaneous reverse and forward rotating fields – its why those motors ‘shake’). The Rotor (the spinning part, called a Squirell Cage because it looks like one) is basically a rotary transformer with a shorted secondary. The motor accelerates because lines of magnetic force are ‘cut’ by the slower rotor attempting to catch up to the rotating field of the stationary stator. If an induction motor it is always trying to catch up with the stator’s field and hence runs slower than the applied frequency. When doing regenerative breaking, the machine is now an induction generator and it is constantly trying to slow down to the decreasing speed of the stator’s revolving magnetic field. If it ever speeds up or slows down enough to be exactly the same speed as the rotating field of the stator, then no motor or generator action… Read more »
Bill Howland

Hi David, please read my explanation below. If the source of the ‘rotating field’ is still unclear, I’ll elaborate.

Spec9

It is amazing how efficient, reliable, and small electric motors are. ICE just are not even in the same ball park as electric motors if you get rid of the energy storage issue. ICE is an inefficient, polluting, noisy, high-maintenance, and smelly technology.

Mint

One thing that gets overlooked when discussing the efficiency advantage is heat.

The Model S motor has been claimed to be almost 90% efficient most of the time, but let’s say it’s 83% efficient at peak power output. That means your fuel (electrons) intake is 500hp, and you get 416 hp at the shaft along with 84hp of heat generation. That needs the cooling system of a dirtbike.

A combustion engine may only be 25% efficient (or less!) at peak output. So to get 416 hp, fuel energy intake is 1700+ hp, and your cooling system needs to remove heat at a rate of 1300 hp! That’s 15 times the heat of the electric motor, equal to ~600 hair dryers at full blast!

That also helps with aerodynamics, as Tesla doesn’t need gobs of air passing through giant radiators.

MDEV

Would this motor been more efficient with a second gear for freeway cruise?

George Bower

The original Roadsters had a 2 speed gear box. but they had bad reliability so they just went to a one speed. I don’t have a motor map for Tesla’s motor but yes my guess is you might pick up some efficiency if you had another gear.

I’m surprised no one here knows the answer to my question about the types of gears Tesla uses though. (see earlier comment)

Boris

What I would love to know is the following:

1. Manufacturing costs of this or any electric motor + transmission vs. 4 cylinder gas engine + automatic transmission
2. If Model S had a multi-gear transmission, would it result in higher range?

Any experts?

ModernMarvelFan

Typical engine (NOT high end) cost for a large auto company is about $2-$5 per HP. So, it is very cheap. Transmission is slightly more expensive, depending on the number of gears. But a typical 4-speed cost about $700 to make. The newer high end 7/8/9 speeds will cost easily double that to make.

The higher volume and automation is what makes them really cheap.

Electric motor can vary a lot depending on the design.

Those are estimate from the project cars that I used to work on.

On EVs, I think the expensive part is the motor controller. Those high powered power electronics should cost more than the motor itself.

Mark

@georges. My understanding is that they are helical gears. Source is teslamotorsclub forum.

Lad

“100% torque at any speed.” Is this true?Typically an induction electric motor has a torque curve that is flat from stall to an rpm of about 3000 to 5000 revolutions, depending on variables like voltage and then it drops off in somewhat of a Knee Shape. I would be completely amazed if the curve was complete flat all the way from zero to max rpm. I think you would have a motor with little or no Back EMF or Eddy Current loss. Anyone have a curve for this motor?

@Dave:
Scott is right. It’s an induction motor and the controller supplies the variable wave forms that cause the rotor and stator magnetic fields to attract and oppose. Note the “stator windings” appear to be copper bars near the rotor.
290 KWs is a huge motor; 440 ft/lbs for 4,600lbs of weight…wow!

The motor in the Leaf is 80 KWs and runs about 200 ft/lbs for the 3,300 lb chassis.

ModernMarvelFan

I think that is “marketing language”.

It is more like a “rated torque” at a wide band of RPMs. From Zero is possible.

All motors will eventually lose torque and efficiency at high rpms due to magnetic saturation. They all drops off after a while. It is just their power band are generally wider and flatter than an Internal Combustion engine.

I would like to see the torque and power curves of the motor and its efficiency rating at various RPM and load…. It will be interesting to know.

Then again, some of that might be company “trade secret”….

Bill Howland
The 4 pole induction motor is the most common motor made, ever. This motor was invented about 130 years ago, so there is no new technology here. The one change is copper rotor bars. They tried aluminum in the early Roadster motors, but kept buring them out, so thats why current Tesla motor rotors in both the Roadster and S have copper bars. As others have mentioned, the 100% torque is only up to 50 mph or so , then it reverts to constant horsepower/decreasing torque. “We all know electric motors have 100% torque from zero speed”. We do? Only certain motors at certain times under certain conditions. Most electric cars, when driven by PWM drives, well yes, but the generalization is made by someone unfamiliar with motor construction or theory. Modern Marvel Fan is the only one here who is making any sense. The only thing I’d say is efficiency does not in general decrease with increased slip. An induction motor must slip since at zero slip there is no motor action. Maximum efficiency in most motors occurs at 80-120% of full load, typically. There will be a fair amount of slip at those loadings depending on the NEMA… Read more »
Lensman

“Lad” asked: “ ‘100% torque at any speed.’ Is this true?”

No. See the graph here (post #38):

http://www.teslamotorsclub.com/showthread.php/17256-The-real-top-speed-of-the-Model-S/page4

Torque is the solid lines; the dotted lines are the power curves.

David Murray

So here’s a better question. Why has Tesla decided to use an induction motor, and everyone else is using permanent magnet motors?

Bill Howland

I’ll bite. Induction motors are the simplest, oldest (about 130 years now) motors around. No mechanism is require to generate a rotating field since the 3 phase source of power intrinsically forms one.

PM motors (relatively new, since historically permanent magnets were weak for their size – in the 1930’s speakers had energized electromagnets since alnico magnets (very strong for their size) hadn’t been invented yet), are slowly overtaking induction motors since although they have higher cost, at low relative speeds their efficiency is higher.

PM motors are increasing used for large applications such as direct drive cooling tower fans, where high efficiency at low speed is important, and the high cost is absorbed by not have an additional speed lowering belt drive system and/or gearbox.

Tesla’s induction motor solution is NOVEL in that it is SO LOW TECH. Just use a plain jane 130 year old high speed motor and a single reduction gearbox for the motor ‘output’. (I realize there is actually a second reduction in the low tech differential, required to go around a corner).

Mint

Tesla’s Mark Tarpenning has a different explanation:
http://www.youtube.com/watch?v=hf15nMnayXk&t=48m41s

I think the reason others are using permanent magnet motors is for the slight efficiency gain, which I suppose is meaningful for smaller batteries, and because they’re low power, so they don’t need too many permanent magnets. I’m sure Marc’s theory has truth as well.

Tesla’s 416hp motor would needs a lot more magnets to use a permanent magnet motor, so they’re not a practical option.

Bill Howland

Not a different explanation, just he’s emphasizing that a plain induction motor requires no rare earths.

Bill Howland
Since Tesla these days is given the credit for inventing the induction motor (I may be splitting hairs, but I give 99% of the credit to George Westinghouse, since even though Thomas Edison did *NOT* invent the lightbulb, he’s effectively given the credit since he’s the one who made it work for hundreds of hours. As TE said, “Invention is 1% inspiration and 99% persperation!”). Westinghouse perfected the ‘design’, what little of it Tesla initially did. And, its not a big stretch to think any number of people would have come up with an induction motor in the nineteenth century anyway. I know you wont believe this, but I’ve hooked up small wires onto large loads and got the wires to dance around just by the current going through them. Hundreds of people working with electricity at the time obviously noticed the same thing and just put the ‘motion’ to good use once they thought about why wires move when current goes through them. Lenz’s law was already very commonly known. They don’t have this as a motto, but they should: “A Tesla isn’t a Tesla without an induction motor namesake.”
ModernMarvelFan

I think that is a trade off.

Volt uses induction motor as well. So did the original EV-1.

1. Induction motors are far cheaper to make.
2. Induction motors with PWM are more complex to control than a simple DC motor or DC brushless motor.
3. I think today’s motors are a blend of the two as in the Spark EV’s motor….

Jeff N

Both motors in the Volt are permanent magnet AC, not induction.

vishal

How many price this motor?