If you happen to be like me (hopefully not), you might have earmarked a one thousand dollar bill for a Model ≡ without fully comprehending the responsibilities you were taking on. I’m not referring to driving your Model ≡, paying for your Model ≡, or even abstaining from keeping your foot pressed all the way down on the accelerator of your Model ≡. Rather I’m referring to the notion that once you take delivery of your car you are inevitably inducted into the unofficial EV public relations department, not only for your ≡, not only for Tesla in general, but as an ambassador of the electric car industry as a whole.
I’m probably overstating this point for the sake of drama, but just imagine what existing electric car owners must spend a portion of their time doing. They are fielding questions about EVs. They are curing ignorance. Dispelling misconceptions. Deprogramming the brainwashed. Directing strangers who want to try out their car to the nearest Tesla showroom. It seems current EV owners are covert emissaries of the electric mindset.
I suspect that’s what happens. Having never driven an EV, I’m assuming that’s the way it is. If it’s not, it likely will be with our generation, given the price and range of the ≡. But since snatching a reservation in April I’ve had an opportunity to realize how profoundly ignorant I am regarding the EV in general, and Tesla specifically. With a 150 mile round-trip commute to town I’ve been watching the evolution of the electric car only out of the corner of one eye. Did I know I wanted one? Hellyeah. Instantly. It was just a matter of time until the variables of price and range lined up in the sites of my desires.
But until recently I’ve only been tracking the industry in a parenthetical manner. I know a few things about Lithium-ion batteries, having recently scoured the planet in search of the best battery for a home solar array. But I didn’t know for example that a gasoline powered car is less than 20% efficient, whereas an electric motor is in the neighborhood of 90% efficient. That’s remarkable.
I did know that a few years ago some upstart EV company had the audacity to call themselves TESLA MOTORS, and had been a little resentful of that, given only one of Nikola’s inventions lie under the hood, with the inventor having invented a world of gadgets well beyond the AC induction motor. But upon reflection, letting go of that [mild] dose of resentment when first hearing Mr. Elon speak about his vision, I suppose that was the first step in curing my ignorances. I became a believer.
And now that an EV, a Tesla EV at that, is nearly parked in my driveway (in the times we live in one or two years goes by in the blink of an eye), it’s time to get the remainder of that ignorance exorcised. Ultimately when some ICE slave approaches my car I want to be prepared to do something with my mouth other than show off my Tesla Grin, and to have something come out of it besides drool. I want to be able to skillfully and authoritatively answer their questions and dispel their anxieties (failing that I’ll just point them to a Tesla store for a test drive). So first a few notes I’ve made, if you’re interested. Most folks likely know all this, but if you don’t you should. Following that a longer comment regarding a couple of questions that perplexed me for a while. And maybe you too.
A few fun facts I didn’t know:
1) For the amount of electricity used to produce a gallon of gasoline, an electric car can go much further on that electricity than that gallon of gas can take a conventional car. Wow.
2) The Depart of Energy has stated that if everyone owned an EV and charged them overnight no new power plants need be built (read my lips: no new power plants!)
3) Tesla does not seek to make a profit on service... since that would be a conflict of interest (what?! Did I just pass through a wormhole?)
4) 5-star crash rating in all categories expected on the Model 3 (Model S got best ever rating partially due to entire front of car being a crumple zone. No engine to end up in the passenger compartment. I feel safer already).
5) Bounty of knowledge here: The Tesla Advantage | Tesla Motors
6) More bounty at this waitbutwhy post by Tim Urban here: How Tesla Will Change The World - Wait But Why. The link takes you into part two of a four part blog post because this section is full of ammunition to fight back against many anti-EV arguments.
7) Tesla gives away its technology (in the form of sharing its patents). And it sells its drive train components. Ex: Toyota RAV4 EV is built on a Tesla drivetrain
8) Dual motors can extend rather than reduce range (it’s like Bizarro world. Everything is reversed)
9) Here’s some enlightening documentaries on the topic of EVs:
Who Killed The Electric Car? (2006)
The story of the rise and fall of GM’s EV-1. Brings a tear to your eye.
Revenge of The Electric Car (2011)
The director of ‘Who Killed The Electric Car?’ returns five years later to document the resuscitation of the EV just as GM is putting the Volt program together at the bequest of long time ICE evangelist turned EV promoter, GM bigwig Bob Lutz. The film documents the mind-shift taking place in the management of GM as well as at Nissan, which we find developing the Leaf. The narration goes heavy into Tesla Motors, documenting the birth of the Roadster on through to the company going public. Be sure to watch the bonus features!
What is the electric car? (2010-12)
This is more an all-round introduction to EVs. Think of it as EV-101. We follow student “Julie” as she takes on doing a paper on the EV for an Environmental Studies class. We follow Julie around as she comes up to speed on electric cars. Person-on-the-street interviews demonstrate just how much EV ignorance is running around out there. One at a time, the considerations about owning an EV are raised and then addressed. A variety of EVs are showcased, including a… pickup truck!? Several EV conversions are shown off. The Model S was out when this was filmed so it is of course included, along with the Roadster. They history of the EV is described, dating back to the very first EV built in …. 1832!
Life with Tesla, The Documentary (2011)
Produced by a Tesla Roadster owner and alternative energy enthusiast who buys an EV to escape the clutch of the oil companies. Includes Tesla employee interviews, arguments for installing home solar panels, quotes from Nikola Tesla, and a handful of priceless expressions on people’s faces as a dashcam captures their reaction to going 0-60 in less than 4 seconds.
Tesla: Master of Lightening’ (2008?)
It seems a Tesla driver really should be up to speed on the basics of Nikola Tesla’s background, life, and accomplishments (and failures). There are a number of documentaries covering this material. I found ‘Tesla: Master of Lightening’ worth recommending. Still need to take in the others. There’s also “Westinghouse’ a documentary describing how George Westinghouse was able to leverage the AC induction motor to win the battle of competing distributed electricity standards over Thomas Edison’s Direct Current approach. Here is a link to a photo of one of Nikola Tesla’s original AC induction motors: Tesla's AC Induction Motor is one of the 10 greatest discoveries of all time
National Geographic - Tesla Motors: The Future of Electric Cars
British made film. Lots of cool footage of the Fremont factory, and a good look at an A-Z build of a Model S. For non-brits you need to know that when the narrator says the word al-u-min’-eee-um he means aluminum:
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Addressing Two Burning Questions
Two questions that I’ve had relate to why Tesla uses an AC motor, and does a Tesla have any kind of transmission. I kept getting conflicting answers on the topics so finally had to go to all the bother of clicking the browser icon and going online. Googling around a bit revealed I wasn’t the only one confused.
Taking the easier question first; “Does a Tesla have a transmission?” … in talking to people (sometimes mechanics) the typical answer received was along the lines of “No. There’s no shifting of gears. The axles are connected directly to the motor.” OK, regarding no shifting of gears, that made sense. An electric motor has a much greater RPM range than any conventional gasoline/diesel motor, and full torque is available at all motor speeds, so changing gears is not mandatory. But the part about the axles connecting directly to the motor did NOT make sense. How could two axles from opposite directions connect directly to the motor? No differential? Well in fact the axles do NOT connect directly to the motor, and all that is required to realize that is to have a peak at the Tesla drive train, as in this photo and Tesla video:
http://s19.postimg.org/6fk41fpkj/drive_train_2.jpg
Notice that in the video Tesla Ben uses the term direct drive. He says “… no transmission, it’s just a direct drive”. Ah ha. I think that “direct drive” sometimes morphs into “the axles are directly connected to the motor” when people are explaining what they think they know. As you can see, there is a gearbox. It just happens to be a single speed gear box. But believe me, there are gears in there. Here is a photo of a Model S gearbox.
http://s19.postimg.org/e75fdqj3n/gearbox_2.jpg
The gear-set on the left is attached directly to the motor (the gear shaft goes through the center of the rotor). You can see the three lugs for the 3 phase power connection in front. Toward the right the technician is handling the differential gear-set that the axles will connect to. The gears are sized to create an overall ratio of 9.73:1 (at least on the MS). This means that the motor makes 9.73 revolutions for every one revolution of the axles. This design enhances torque, but also dictates the top speed of the vehicle. Not to worry, the motor allows for relatively high RPMs to achieve the coveted 100+ MPH road speeds. By the way, that gearbox is filled with oil. I assume ATF? (Automatic Transmission Fluid). Gears require lubrication. So although there are no traditional 3,000 mile oil changes, the gearbox oil does have to be changed out periodically.
Interestingly enough there's a design out there that does have the axles connecting directly to the motor. Below is a photo of the Chevy Spark EV drive train. It is termed a coaxial drive unit, as the axles and motor are on the same axis. But, this ain’t what Tesla did!
http://s19.postimg.org/ptpjev6er/spark_ev_coaxle_gearbox.jpg
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Now for the motor. The question is: “Why does Tesla use an AC motor instead of a DC motor, given that the battery makes DC power?” In fact there are a number of extra components required to allow an AC motor to operate with DC power, so why bother? I found plenty of answers to this question, but in my view you either get overly simplistic replies or overly technical descriptions on the subject. I might as well have been asking where the polar bear came from on the last season of Lost, or do androids in fact dream of electric sheep, for all the satisfaction I got. So here is an attempt to answer the question. Actually it’s a staged answer that gets more technical as we proceed, so feel free to hop off when you've had enough.
Answer for Normal Human Beings
The shortest and simplest answer as to why an AC motor over a DC motor is… “because”. And that will suffice for some. No worries. But if the question is explored a bit further, someone with knowledge of the History of Tesla Motors will give you a slightly more elaborate because, which is that the prototype EV that Tesla Motors bought was already using an AC motor. True. Further, it’s been pointed out that if a DC motor had been used then Tesla Motors could not be called Tesla Motors, given that Nikola Tesla was into AC, not DC. A bit cheeky, but true enough.
Geek Level 1
The next level of explanation is that by using an AC motor, in particular a version of Nikola Tesla’s AC induction motor, that parts most susceptible to supply issues, cost increases, wearing out, etc. are reduced. The parts that wear out are the so-called brushes sometimes found in DC motors because they physically engage a rotating shaft and friction occurs. The other parts eliminated were permanent magnets. The kind of magnets often used in electric motors are rare-earth magnets because they are very powerful, but China has most of the rare earth deposits so... you know. Besides being expensive, permanent magnets can break, demagnetize, add weight, and there are alternatives that allow for more control over the magnetic fields they produce. It is in fact AC current that actually substitutes for the magnets.
Line up all those answers and you've got a reasonable and only slightly geeky explanation justifying Tesla Motors' use of an AC motor. Cost savings, weight savings, legacy, elimination of parts that wear out, and more control. So we’re done, right?
Geek Level 2
Right. Unless you’re a geek like me and are still saying “Why?”. Spewing out facts like brushes wear out and AC substitutes for magnets is too abstract to allow for a deeper understanding. There’s no context to fit the information together. You don’t know what they used instead of brushes, or what it is it about Nikola Tesla’s 100+ year old invention that allowed the magnets to come out. I finally found a more robust explanation, but not in any one place, so for inquiring minds here is my best shot at assembling a fuller but hopefully not over-technical explanation.
Before going further it helps to understand one basic (and very cool) thing about electric motors. Electric motors (AC or DC) are all about magnetic fields. Magnetism is the name of this game. The Electromagnetic Force is one of the four fundamental forces of nature (the others being the Gravitational Force, the Strong Force [holds atoms together], and the Weak Force [decay of fundamental particles]).
Electromagnetism is the superhero force that makes motors spin. Just think for a second about how two magnets facing each other with the same polarity tend to repel (north pole to north pole, or south pole to south pole), and likewise how magnets pull together when opposite polarities are facing (opposites attract). So imagine if you were to duct tape a bunch of magnets to say, a Lazy Susan, and then place some other magnet near that bundle, what would happen?. That's basically how electric motors work. And the bigger the magnets the more powerful the force that spins the cylinder. Whether powered by magnets or an ICE, the twisting force that spins a motor is termed torque. The stronger the magnetic fields the more torque. Torque comes in pretty handy in an automobile.
When designing an electric motor there are several ways to come up with these all important magnetic fields. One way is with natural, or permanent magnets. Some minerals are naturally magnetized and emit an electromagnetic field. On the other hand if you go to the trouble of formulating an alloy using the rare-earth element Neodymium you get a very serious magnet that motor designers love (more torque). A second way to make a magnetic field is if you take a few wrappings of copper wire and apply a DC (direct current) voltage to the winding. The coil will emit an electromagnetic field. Thirdly, you can create an electromagnetic field with AC (alternating current), but we’re going to save that one for a moment. Given what’s been said we have now enough of a primer to talk about brushes and AC induction motors in a way that will hopefully make sense and not be some abstract notion.
BRUSHES
In simple terms traditional DC motors work by surrounding a rotating shaft with windings of copper wire that are energized by a DC power source (termed an armature because the wires are wrapped around the arms of a metal frame). The rotor is then surrounded by another magnetic field from a fixed position, which is accomplished with a case encircling the rotor that has permanent magnets adhered to the inside of the case (this sort of rig is called a stator because it is stationary).
The problem is how to get power to the coil on the rotor since it will be spinning (to make the wheels on the car go round and round). This is where brushes come in. What you do is press a conductive material against the rotor, as shown in this image:
http://s19.postimg.org/qki9kn8s3/chaudhary_DCmotor.png
As you can see, a pair of carbon brushes (one for positive and one for negative) are connected to the DC leads. The brushes then make physical contact with a designated area near the end of the rotor that distributes the voltage to the armature (it’s called a commutator because it commutes the current across). The weakness of this design is that you have two parts rubbing against each other, and the [softer] brushes eventually wear down to a nub and must be replaced. You don’t want brushes wearing out in traffic so this is why a brushed motor is a no-starter in an EV. (btw – from a green perspective you don’t want to be around a brushed motor. As the brushes wear out they spew nasty particles of carbon or graphite into the air. Brushed motors contribute in some small way to air pollution).
Now as is happens the DC motor evolved some time ago into a version not requiring brushes. Some clever person had the brilliant idea of moving the permanent magnets from the stator to the rotor, and moving the coils of wire from the rotor to the stator. With this advance the DC leads could easily be attached to the coils on the stationary part of the motor. There was no longer a need to get electricity to the rotor.
MAGNETS
However the magnets still remained. For all the reasons cited above they need to go too. And this is where we get the opportunity to comprehend the brilliance of the AC induction motor used in a Tesla.
Enter AC or alternating current. Unlike DC voltage, which has constant polarity (like a AA battery with a positive and a negative end), AC changes from positive to negative several times a second (it alternates the polarity from + to -). Alternating current creates an oscillating sine wave. To take household wiring as an example the voltage goes from zero volts to a positive 120 volts … then ramps down to zero volts. It then repeats, only with the polarity reversed. This occurs 60 times a second. Here’s an image of an AC sine wave:
http://s19.postimg.org/z468w56ib/sinewave.png
So, why do we care? Because each time the voltage rises and falls AN ELECTROMAGNETIC FIELD IS CREATED. This is a new, third way, to make a magnetic field. Great. But how does this help our motor? Recall that you don’t want coils of wire around the rotor because they must be powered through brushes. And you don’t want magnets around the rotor either. So what you do instead is use a chunk of conductive material like aluminum or copper for the rotor, and you energize the coils in the stator with alternating current instead of DC. With AC behaving as it does the coils will produce an electromagnetic field that extends all the way to the rotor. The field reacts with the highly conductive metal on the rotor to induce a current to flow on the rotor. And just as with the AC current creating electromagnetic fields in the stator, the current flowing on the rotor in turn creates a field around the rotor.
Whoa. Did you get that? Without having to understand the physics of what creates an electromagnetic field or how an electromagnetic field could induce a current flow, the point is that all of a sudden the rotor is creating a magnetic field in tune to the cycling of the AC current feeding the stator. No electricity is wired to the rotor. No permanent magnets are attached to the rotor. Yet a magnetic field has been produced. Without all the fuss of brushes and rare earth magnets we’re back to having the all-important two opposing magnetic fields that make a motor spin.
So once again: Coils of wire on the stator > apply an alternating current to the coils > an electromagnetic field is created that reaches the rotor > a current is INDUCED to flow on the conductive rotor > that current flow emits an electromagnetic field on the rotor. Voilà. The AC inductive motor.
Here’s an animation of that principal. Scroll down to “How does an AC induction motor work?”
AC induction motors | How AC motors work
Thank you Nikola Tesla for figuring that out!
Geek Level 3
When you start applying these principals to the motor used in a Tesla automobile be aware of the following. Tesla uses what’s termed a 3-phase 4-pole motor. Starting with the ‘4 pole’ part, that just means that the Tesla motor has four sets of coiled wires in the stator, which again is the stationary part enclosing the rotor. Insulated copper wire is used, and since the wire is wound many many times around a laminated steel frame the term windings is often used. Picture an apple pie cut in four slices. That gives you an idea of the topography of the windings, which sit at the fat end of each slice. Each set of windings are connected to an AC source, and thus all four sets produce an electromagnetic field. As noted, the fields constantly change polarity, thus their magnetic fields are switching from magnetic north (N) to magnetic south (S). This is referred to as pole, just like the earth’s North and South poles. There are four sets of windings (coils), thus we have a 4 pole motor.
Now the fun part. What is this 3 phase business all about? It’s easy. 3 phase AC is just three sources of AC power. It takes the form of three separate cables. Think of AC phases as cylinders in a conventional ICE car. The more cylinders (power sources) the smoother the engine runs. Right? A V8 runs smoother than a 4 cylinder engine and has more power. Likewise you get more work done with 3-phase power than the typical single phase source from a home outlet.
Here’s how the power is applied. This is the last step in the rudimentary understanding we are developing as to how the AC 3-phase 4-pole induction motor works. All three phases are connected to the windings on each of the four poles. The windings on each individual pole is wired in such a way that three distinct loops exist. That’s three separate windings for each coil. The windings are physically adjacent to one another as shown in this image:
http://s19.postimg.org/hfei4iur7/windings.jpg
Here’s the key to the whole thing. Power is NOT applied to all three loops of a pole simultaneously. Instead the first AC lead, let’s call it phase A, is powered up and instantly an electromagnetic field is created. The field strengthens as the voltage rises to the top of the wave. Then after a moment phase B is energized. Thus the second magnetic field is staggered or out of phase with the first. The effect is that the relative electromagnetic fields are not the same strength. Finally phase C is energized a moment later. It too is out of phase with the others (bear in mind we are still focusing on just one pole).
Each of the three electromagnetic fields are interacting with the rotor and creating opposing electromagnetic fields. This opposition, or force, pulls on the rotor and it turns. You can start to see how smooth this process is because each stator field in turn dominates the action. As the field from phase A weakens, the field from phase B, which is physically adjacent to A, is peaking. As the field from phase B weakens the field from physically adjacent phase C is peaking. In each case the rotor is being dragged progressively along by the electromagnetic fields emitting from the progressively spaced windings.
Now multiply that whole process times four. The other three sets of windings are getting in on the action too. In effect you have a constantly rotating magnetic field progressing around the entire circumference of the rotor. Very smooth. This is all synchronized by a controller for best efficiency. The rotor will spin indefinitely as long as AC power is applied. Motor speed is controlled by varying the frequency of the AC waves. The higher the frequency, the quicker the electromagnetic fields rise and fall, and the faster the motor spins. ---- It would be awesome if someone were to create a proper animation of this process of turning invisible electromagnetic energy into mechanical energy. It all strikes me as a bit of a symphony of movement... a sort of dance.
Anyway, that’s the simplified but hopefully clear answer. The AC induction motor is so righteously suited to an EV (like better regen capability) that it’s worth the trouble of converting the battery voltage to into AC. And it’s even worth the trouble of also having to convert the AC voltage produced during regen to the DC voltage needed to charge the battery. These days transitioning from DC to AC or vice versa is no big deal. A modern AC diesel generator on my property makes the transition three times all for the sake of efficiency of operation.
NOTE: To avoid confusion be aware that an above link to the excellent Tim Urban waitbutwhy blog post, as well as the link to an awesome How It's Made - Dream Cars video below each have sections describing how the motor works... and neither one quite nails it. So don't be confused by their slightly erroneous descriptions and animations. (And please forgive my minor quibble).
BTW – Tesla uses a copper rotor for its motors in lieu of aluminum due to copper’s much better conductivity. It’s far more difficult and costly to make rotors out of copper but you get a more efficient motor.
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CREDITS: Thanks to Ivan over at Ivan’s Garage for filling in the blanks of my knowledge. Ivan winds his own electric motors so he knows a thing or two about the AC inductive motor. (Ivan's Garage, Electric Vehicles, AC Electric Motors - Index)
For completeness it should be noted that you could in fact pull all this magic off with a DC motor. A gentleman named Wally Rippel who helped develop the motor for the EV-1 and later worked at Tesla Motors talks about how closely related brushless DC and brushless AC motors are. He does end up siding with the AC motor though, citing PERFORMANCE advantages: Induction Versus DC Brushless Motors
Another great blog thread is from 2006 where co-founder Martin Eberhard discusses induction motors: Motor City
Here’s a great video from a show called "How It's Made - Dream Cars showing a detailed assembly of Model S. At 6 min in they show the motor being assembled. (updated to include the preferred video).
S02E10 - Tesla Model S.mkv
Nice video explaining 3 phase motors:
And here is a generic thread on copper rotors: MOTOR Magazine | Powertrains | Copper Rotor Induction Motors to Power EVs — Copper is a Viable Alternative to Expensive Rare Earths
Older animation explaining how magnetism works. Good for kids too:
Video of a Tesla drive unit on display in the showroom of a Tesla store in Boulder Colorado:
Hopefully these videos will make more sense having become familiar with some of the terminology used in electric motors and how AC can make them work better.
END
I’m probably overstating this point for the sake of drama, but just imagine what existing electric car owners must spend a portion of their time doing. They are fielding questions about EVs. They are curing ignorance. Dispelling misconceptions. Deprogramming the brainwashed. Directing strangers who want to try out their car to the nearest Tesla showroom. It seems current EV owners are covert emissaries of the electric mindset.
I suspect that’s what happens. Having never driven an EV, I’m assuming that’s the way it is. If it’s not, it likely will be with our generation, given the price and range of the ≡. But since snatching a reservation in April I’ve had an opportunity to realize how profoundly ignorant I am regarding the EV in general, and Tesla specifically. With a 150 mile round-trip commute to town I’ve been watching the evolution of the electric car only out of the corner of one eye. Did I know I wanted one? Hellyeah. Instantly. It was just a matter of time until the variables of price and range lined up in the sites of my desires.
But until recently I’ve only been tracking the industry in a parenthetical manner. I know a few things about Lithium-ion batteries, having recently scoured the planet in search of the best battery for a home solar array. But I didn’t know for example that a gasoline powered car is less than 20% efficient, whereas an electric motor is in the neighborhood of 90% efficient. That’s remarkable.
I did know that a few years ago some upstart EV company had the audacity to call themselves TESLA MOTORS, and had been a little resentful of that, given only one of Nikola’s inventions lie under the hood, with the inventor having invented a world of gadgets well beyond the AC induction motor. But upon reflection, letting go of that [mild] dose of resentment when first hearing Mr. Elon speak about his vision, I suppose that was the first step in curing my ignorances. I became a believer.
And now that an EV, a Tesla EV at that, is nearly parked in my driveway (in the times we live in one or two years goes by in the blink of an eye), it’s time to get the remainder of that ignorance exorcised. Ultimately when some ICE slave approaches my car I want to be prepared to do something with my mouth other than show off my Tesla Grin, and to have something come out of it besides drool. I want to be able to skillfully and authoritatively answer their questions and dispel their anxieties (failing that I’ll just point them to a Tesla store for a test drive). So first a few notes I’ve made, if you’re interested. Most folks likely know all this, but if you don’t you should. Following that a longer comment regarding a couple of questions that perplexed me for a while. And maybe you too.
A few fun facts I didn’t know:
1) For the amount of electricity used to produce a gallon of gasoline, an electric car can go much further on that electricity than that gallon of gas can take a conventional car. Wow.
2) The Depart of Energy has stated that if everyone owned an EV and charged them overnight no new power plants need be built (read my lips: no new power plants!)
3) Tesla does not seek to make a profit on service... since that would be a conflict of interest (what?! Did I just pass through a wormhole?)
4) 5-star crash rating in all categories expected on the Model 3 (Model S got best ever rating partially due to entire front of car being a crumple zone. No engine to end up in the passenger compartment. I feel safer already).
5) Bounty of knowledge here: The Tesla Advantage | Tesla Motors
6) More bounty at this waitbutwhy post by Tim Urban here: How Tesla Will Change The World - Wait But Why. The link takes you into part two of a four part blog post because this section is full of ammunition to fight back against many anti-EV arguments.
7) Tesla gives away its technology (in the form of sharing its patents). And it sells its drive train components. Ex: Toyota RAV4 EV is built on a Tesla drivetrain
8) Dual motors can extend rather than reduce range (it’s like Bizarro world. Everything is reversed)
9) Here’s some enlightening documentaries on the topic of EVs:
Who Killed The Electric Car? (2006)
The story of the rise and fall of GM’s EV-1. Brings a tear to your eye.
Revenge of The Electric Car (2011)
The director of ‘Who Killed The Electric Car?’ returns five years later to document the resuscitation of the EV just as GM is putting the Volt program together at the bequest of long time ICE evangelist turned EV promoter, GM bigwig Bob Lutz. The film documents the mind-shift taking place in the management of GM as well as at Nissan, which we find developing the Leaf. The narration goes heavy into Tesla Motors, documenting the birth of the Roadster on through to the company going public. Be sure to watch the bonus features!
What is the electric car? (2010-12)
This is more an all-round introduction to EVs. Think of it as EV-101. We follow student “Julie” as she takes on doing a paper on the EV for an Environmental Studies class. We follow Julie around as she comes up to speed on electric cars. Person-on-the-street interviews demonstrate just how much EV ignorance is running around out there. One at a time, the considerations about owning an EV are raised and then addressed. A variety of EVs are showcased, including a… pickup truck!? Several EV conversions are shown off. The Model S was out when this was filmed so it is of course included, along with the Roadster. They history of the EV is described, dating back to the very first EV built in …. 1832!
Life with Tesla, The Documentary (2011)
Produced by a Tesla Roadster owner and alternative energy enthusiast who buys an EV to escape the clutch of the oil companies. Includes Tesla employee interviews, arguments for installing home solar panels, quotes from Nikola Tesla, and a handful of priceless expressions on people’s faces as a dashcam captures their reaction to going 0-60 in less than 4 seconds.
Tesla: Master of Lightening’ (2008?)
It seems a Tesla driver really should be up to speed on the basics of Nikola Tesla’s background, life, and accomplishments (and failures). There are a number of documentaries covering this material. I found ‘Tesla: Master of Lightening’ worth recommending. Still need to take in the others. There’s also “Westinghouse’ a documentary describing how George Westinghouse was able to leverage the AC induction motor to win the battle of competing distributed electricity standards over Thomas Edison’s Direct Current approach. Here is a link to a photo of one of Nikola Tesla’s original AC induction motors: Tesla's AC Induction Motor is one of the 10 greatest discoveries of all time
National Geographic - Tesla Motors: The Future of Electric Cars
British made film. Lots of cool footage of the Fremont factory, and a good look at an A-Z build of a Model S. For non-brits you need to know that when the narrator says the word al-u-min’-eee-um he means aluminum:
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Addressing Two Burning Questions
Two questions that I’ve had relate to why Tesla uses an AC motor, and does a Tesla have any kind of transmission. I kept getting conflicting answers on the topics so finally had to go to all the bother of clicking the browser icon and going online. Googling around a bit revealed I wasn’t the only one confused.
Taking the easier question first; “Does a Tesla have a transmission?” … in talking to people (sometimes mechanics) the typical answer received was along the lines of “No. There’s no shifting of gears. The axles are connected directly to the motor.” OK, regarding no shifting of gears, that made sense. An electric motor has a much greater RPM range than any conventional gasoline/diesel motor, and full torque is available at all motor speeds, so changing gears is not mandatory. But the part about the axles connecting directly to the motor did NOT make sense. How could two axles from opposite directions connect directly to the motor? No differential? Well in fact the axles do NOT connect directly to the motor, and all that is required to realize that is to have a peak at the Tesla drive train, as in this photo and Tesla video:
http://s19.postimg.org/6fk41fpkj/drive_train_2.jpg
Notice that in the video Tesla Ben uses the term direct drive. He says “… no transmission, it’s just a direct drive”. Ah ha. I think that “direct drive” sometimes morphs into “the axles are directly connected to the motor” when people are explaining what they think they know. As you can see, there is a gearbox. It just happens to be a single speed gear box. But believe me, there are gears in there. Here is a photo of a Model S gearbox.
http://s19.postimg.org/e75fdqj3n/gearbox_2.jpg
The gear-set on the left is attached directly to the motor (the gear shaft goes through the center of the rotor). You can see the three lugs for the 3 phase power connection in front. Toward the right the technician is handling the differential gear-set that the axles will connect to. The gears are sized to create an overall ratio of 9.73:1 (at least on the MS). This means that the motor makes 9.73 revolutions for every one revolution of the axles. This design enhances torque, but also dictates the top speed of the vehicle. Not to worry, the motor allows for relatively high RPMs to achieve the coveted 100+ MPH road speeds. By the way, that gearbox is filled with oil. I assume ATF? (Automatic Transmission Fluid). Gears require lubrication. So although there are no traditional 3,000 mile oil changes, the gearbox oil does have to be changed out periodically.
Interestingly enough there's a design out there that does have the axles connecting directly to the motor. Below is a photo of the Chevy Spark EV drive train. It is termed a coaxial drive unit, as the axles and motor are on the same axis. But, this ain’t what Tesla did!
http://s19.postimg.org/ptpjev6er/spark_ev_coaxle_gearbox.jpg
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Now for the motor. The question is: “Why does Tesla use an AC motor instead of a DC motor, given that the battery makes DC power?” In fact there are a number of extra components required to allow an AC motor to operate with DC power, so why bother? I found plenty of answers to this question, but in my view you either get overly simplistic replies or overly technical descriptions on the subject. I might as well have been asking where the polar bear came from on the last season of Lost, or do androids in fact dream of electric sheep, for all the satisfaction I got. So here is an attempt to answer the question. Actually it’s a staged answer that gets more technical as we proceed, so feel free to hop off when you've had enough.
Answer for Normal Human Beings
The shortest and simplest answer as to why an AC motor over a DC motor is… “because”. And that will suffice for some. No worries. But if the question is explored a bit further, someone with knowledge of the History of Tesla Motors will give you a slightly more elaborate because, which is that the prototype EV that Tesla Motors bought was already using an AC motor. True. Further, it’s been pointed out that if a DC motor had been used then Tesla Motors could not be called Tesla Motors, given that Nikola Tesla was into AC, not DC. A bit cheeky, but true enough.
Geek Level 1
The next level of explanation is that by using an AC motor, in particular a version of Nikola Tesla’s AC induction motor, that parts most susceptible to supply issues, cost increases, wearing out, etc. are reduced. The parts that wear out are the so-called brushes sometimes found in DC motors because they physically engage a rotating shaft and friction occurs. The other parts eliminated were permanent magnets. The kind of magnets often used in electric motors are rare-earth magnets because they are very powerful, but China has most of the rare earth deposits so... you know. Besides being expensive, permanent magnets can break, demagnetize, add weight, and there are alternatives that allow for more control over the magnetic fields they produce. It is in fact AC current that actually substitutes for the magnets.
Line up all those answers and you've got a reasonable and only slightly geeky explanation justifying Tesla Motors' use of an AC motor. Cost savings, weight savings, legacy, elimination of parts that wear out, and more control. So we’re done, right?
Geek Level 2
Right. Unless you’re a geek like me and are still saying “Why?”. Spewing out facts like brushes wear out and AC substitutes for magnets is too abstract to allow for a deeper understanding. There’s no context to fit the information together. You don’t know what they used instead of brushes, or what it is it about Nikola Tesla’s 100+ year old invention that allowed the magnets to come out. I finally found a more robust explanation, but not in any one place, so for inquiring minds here is my best shot at assembling a fuller but hopefully not over-technical explanation.
Before going further it helps to understand one basic (and very cool) thing about electric motors. Electric motors (AC or DC) are all about magnetic fields. Magnetism is the name of this game. The Electromagnetic Force is one of the four fundamental forces of nature (the others being the Gravitational Force, the Strong Force [holds atoms together], and the Weak Force [decay of fundamental particles]).
Electromagnetism is the superhero force that makes motors spin. Just think for a second about how two magnets facing each other with the same polarity tend to repel (north pole to north pole, or south pole to south pole), and likewise how magnets pull together when opposite polarities are facing (opposites attract). So imagine if you were to duct tape a bunch of magnets to say, a Lazy Susan, and then place some other magnet near that bundle, what would happen?. That's basically how electric motors work. And the bigger the magnets the more powerful the force that spins the cylinder. Whether powered by magnets or an ICE, the twisting force that spins a motor is termed torque. The stronger the magnetic fields the more torque. Torque comes in pretty handy in an automobile.
When designing an electric motor there are several ways to come up with these all important magnetic fields. One way is with natural, or permanent magnets. Some minerals are naturally magnetized and emit an electromagnetic field. On the other hand if you go to the trouble of formulating an alloy using the rare-earth element Neodymium you get a very serious magnet that motor designers love (more torque). A second way to make a magnetic field is if you take a few wrappings of copper wire and apply a DC (direct current) voltage to the winding. The coil will emit an electromagnetic field. Thirdly, you can create an electromagnetic field with AC (alternating current), but we’re going to save that one for a moment. Given what’s been said we have now enough of a primer to talk about brushes and AC induction motors in a way that will hopefully make sense and not be some abstract notion.
BRUSHES
In simple terms traditional DC motors work by surrounding a rotating shaft with windings of copper wire that are energized by a DC power source (termed an armature because the wires are wrapped around the arms of a metal frame). The rotor is then surrounded by another magnetic field from a fixed position, which is accomplished with a case encircling the rotor that has permanent magnets adhered to the inside of the case (this sort of rig is called a stator because it is stationary).
The problem is how to get power to the coil on the rotor since it will be spinning (to make the wheels on the car go round and round). This is where brushes come in. What you do is press a conductive material against the rotor, as shown in this image:
http://s19.postimg.org/qki9kn8s3/chaudhary_DCmotor.png
As you can see, a pair of carbon brushes (one for positive and one for negative) are connected to the DC leads. The brushes then make physical contact with a designated area near the end of the rotor that distributes the voltage to the armature (it’s called a commutator because it commutes the current across). The weakness of this design is that you have two parts rubbing against each other, and the [softer] brushes eventually wear down to a nub and must be replaced. You don’t want brushes wearing out in traffic so this is why a brushed motor is a no-starter in an EV. (btw – from a green perspective you don’t want to be around a brushed motor. As the brushes wear out they spew nasty particles of carbon or graphite into the air. Brushed motors contribute in some small way to air pollution).
Now as is happens the DC motor evolved some time ago into a version not requiring brushes. Some clever person had the brilliant idea of moving the permanent magnets from the stator to the rotor, and moving the coils of wire from the rotor to the stator. With this advance the DC leads could easily be attached to the coils on the stationary part of the motor. There was no longer a need to get electricity to the rotor.
MAGNETS
However the magnets still remained. For all the reasons cited above they need to go too. And this is where we get the opportunity to comprehend the brilliance of the AC induction motor used in a Tesla.
Enter AC or alternating current. Unlike DC voltage, which has constant polarity (like a AA battery with a positive and a negative end), AC changes from positive to negative several times a second (it alternates the polarity from + to -). Alternating current creates an oscillating sine wave. To take household wiring as an example the voltage goes from zero volts to a positive 120 volts … then ramps down to zero volts. It then repeats, only with the polarity reversed. This occurs 60 times a second. Here’s an image of an AC sine wave:
http://s19.postimg.org/z468w56ib/sinewave.png
So, why do we care? Because each time the voltage rises and falls AN ELECTROMAGNETIC FIELD IS CREATED. This is a new, third way, to make a magnetic field. Great. But how does this help our motor? Recall that you don’t want coils of wire around the rotor because they must be powered through brushes. And you don’t want magnets around the rotor either. So what you do instead is use a chunk of conductive material like aluminum or copper for the rotor, and you energize the coils in the stator with alternating current instead of DC. With AC behaving as it does the coils will produce an electromagnetic field that extends all the way to the rotor. The field reacts with the highly conductive metal on the rotor to induce a current to flow on the rotor. And just as with the AC current creating electromagnetic fields in the stator, the current flowing on the rotor in turn creates a field around the rotor.
Whoa. Did you get that? Without having to understand the physics of what creates an electromagnetic field or how an electromagnetic field could induce a current flow, the point is that all of a sudden the rotor is creating a magnetic field in tune to the cycling of the AC current feeding the stator. No electricity is wired to the rotor. No permanent magnets are attached to the rotor. Yet a magnetic field has been produced. Without all the fuss of brushes and rare earth magnets we’re back to having the all-important two opposing magnetic fields that make a motor spin.
So once again: Coils of wire on the stator > apply an alternating current to the coils > an electromagnetic field is created that reaches the rotor > a current is INDUCED to flow on the conductive rotor > that current flow emits an electromagnetic field on the rotor. Voilà. The AC inductive motor.
Here’s an animation of that principal. Scroll down to “How does an AC induction motor work?”
AC induction motors | How AC motors work
Thank you Nikola Tesla for figuring that out!
Geek Level 3
When you start applying these principals to the motor used in a Tesla automobile be aware of the following. Tesla uses what’s termed a 3-phase 4-pole motor. Starting with the ‘4 pole’ part, that just means that the Tesla motor has four sets of coiled wires in the stator, which again is the stationary part enclosing the rotor. Insulated copper wire is used, and since the wire is wound many many times around a laminated steel frame the term windings is often used. Picture an apple pie cut in four slices. That gives you an idea of the topography of the windings, which sit at the fat end of each slice. Each set of windings are connected to an AC source, and thus all four sets produce an electromagnetic field. As noted, the fields constantly change polarity, thus their magnetic fields are switching from magnetic north (N) to magnetic south (S). This is referred to as pole, just like the earth’s North and South poles. There are four sets of windings (coils), thus we have a 4 pole motor.
Now the fun part. What is this 3 phase business all about? It’s easy. 3 phase AC is just three sources of AC power. It takes the form of three separate cables. Think of AC phases as cylinders in a conventional ICE car. The more cylinders (power sources) the smoother the engine runs. Right? A V8 runs smoother than a 4 cylinder engine and has more power. Likewise you get more work done with 3-phase power than the typical single phase source from a home outlet.
Here’s how the power is applied. This is the last step in the rudimentary understanding we are developing as to how the AC 3-phase 4-pole induction motor works. All three phases are connected to the windings on each of the four poles. The windings on each individual pole is wired in such a way that three distinct loops exist. That’s three separate windings for each coil. The windings are physically adjacent to one another as shown in this image:
http://s19.postimg.org/hfei4iur7/windings.jpg
Here’s the key to the whole thing. Power is NOT applied to all three loops of a pole simultaneously. Instead the first AC lead, let’s call it phase A, is powered up and instantly an electromagnetic field is created. The field strengthens as the voltage rises to the top of the wave. Then after a moment phase B is energized. Thus the second magnetic field is staggered or out of phase with the first. The effect is that the relative electromagnetic fields are not the same strength. Finally phase C is energized a moment later. It too is out of phase with the others (bear in mind we are still focusing on just one pole).
Each of the three electromagnetic fields are interacting with the rotor and creating opposing electromagnetic fields. This opposition, or force, pulls on the rotor and it turns. You can start to see how smooth this process is because each stator field in turn dominates the action. As the field from phase A weakens, the field from phase B, which is physically adjacent to A, is peaking. As the field from phase B weakens the field from physically adjacent phase C is peaking. In each case the rotor is being dragged progressively along by the electromagnetic fields emitting from the progressively spaced windings.
Now multiply that whole process times four. The other three sets of windings are getting in on the action too. In effect you have a constantly rotating magnetic field progressing around the entire circumference of the rotor. Very smooth. This is all synchronized by a controller for best efficiency. The rotor will spin indefinitely as long as AC power is applied. Motor speed is controlled by varying the frequency of the AC waves. The higher the frequency, the quicker the electromagnetic fields rise and fall, and the faster the motor spins. ---- It would be awesome if someone were to create a proper animation of this process of turning invisible electromagnetic energy into mechanical energy. It all strikes me as a bit of a symphony of movement... a sort of dance.
Anyway, that’s the simplified but hopefully clear answer. The AC induction motor is so righteously suited to an EV (like better regen capability) that it’s worth the trouble of converting the battery voltage to into AC. And it’s even worth the trouble of also having to convert the AC voltage produced during regen to the DC voltage needed to charge the battery. These days transitioning from DC to AC or vice versa is no big deal. A modern AC diesel generator on my property makes the transition three times all for the sake of efficiency of operation.
NOTE: To avoid confusion be aware that an above link to the excellent Tim Urban waitbutwhy blog post, as well as the link to an awesome How It's Made - Dream Cars video below each have sections describing how the motor works... and neither one quite nails it. So don't be confused by their slightly erroneous descriptions and animations. (And please forgive my minor quibble).
BTW – Tesla uses a copper rotor for its motors in lieu of aluminum due to copper’s much better conductivity. It’s far more difficult and costly to make rotors out of copper but you get a more efficient motor.
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CREDITS: Thanks to Ivan over at Ivan’s Garage for filling in the blanks of my knowledge. Ivan winds his own electric motors so he knows a thing or two about the AC inductive motor. (Ivan's Garage, Electric Vehicles, AC Electric Motors - Index)
For completeness it should be noted that you could in fact pull all this magic off with a DC motor. A gentleman named Wally Rippel who helped develop the motor for the EV-1 and later worked at Tesla Motors talks about how closely related brushless DC and brushless AC motors are. He does end up siding with the AC motor though, citing PERFORMANCE advantages: Induction Versus DC Brushless Motors
Another great blog thread is from 2006 where co-founder Martin Eberhard discusses induction motors: Motor City
Here’s a great video from a show called "How It's Made - Dream Cars showing a detailed assembly of Model S. At 6 min in they show the motor being assembled. (updated to include the preferred video).
S02E10 - Tesla Model S.mkv
Nice video explaining 3 phase motors:
And here is a generic thread on copper rotors: MOTOR Magazine | Powertrains | Copper Rotor Induction Motors to Power EVs — Copper is a Viable Alternative to Expensive Rare Earths
Older animation explaining how magnetism works. Good for kids too:
Video of a Tesla drive unit on display in the showroom of a Tesla store in Boulder Colorado:
Hopefully these videos will make more sense having become familiar with some of the terminology used in electric motors and how AC can make them work better.
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