On Tesla's induction motor

http://www.economist.com/blogs/babbage/2011/04/induction_motors

by colinprince • 15 years ago

157 77 15 years ago

Interesting point to note here (since this article seems to float from point to point) is the fact that tesla's battery to wheels efficiency ratio is 88%, which the article states is 4x the average. Seems to me like Toyota's investment in tesla was a better deal than we initially assumed.

eru6• 15 years ago

Nothing to write home about. Electric engines are efficient.

If you look at the efficiency from, say, coal burned in the power station to electricity in the batteries to driving, electric cars fare similar to internal combustion engines. (Burning your fuel in the big power station is more efficient than a car's internal combustion engine, but going through the extra steps of transmitting the energy to your home and then into the batteries eats some of that.)

JoachimSchipper• 15 years ago

This is rarely mentioned explicitly, but seems to be behind many of the "green car" claims: uranium "burned" in the power station is CO2-neutral, cheap and plentiful (even in politically stable regions.)

rickmode2• 15 years ago

Consider transportation of oil and gas (petrol / auto gasoline) along with gas refining versus electricity generation and transmission.

In any case full electric cars allow centralized power generation, in turn allowing more opportunities for clean power.

brianbreslin3• 15 years ago

well were they comparing the 88% to regular combustion engines or existing electric/hybrid cars?

otterley• 15 years ago

Consider, too, that the diesel engines in large locomotives are basically rolling power plants. The diesel fuel doesn't directly power the drive train; it's used to generate electricity to power its electric motors.

kragen6• 15 years ago

Some electric motors are 95% efficient.

85-90%: typical brushless DC motors: http://en.wikipedia.org/wiki/Electric_motor#Brushless_DC_mot...

92.4%: minimum standard for 125hp NEMA B motors: http://www.engineeringtoolbox.com/electrical-motor-efficienc...

96%: new record efficiency achieved in 2009: http://newenergyandfuel.com/http:/newenergyandfuel/com/2009/...

arepb• 15 years ago

One of the biggest benefits -- which thankfully gets a line or so halfway down -- is that induction motors require far less cooling accessories. This is big for cost and weight savings.

adovenmuehle• 15 years ago

A good point. With low weight and maximum torque from 0 to 6000 rpm, it will be interesting to see what performance cars will look like in 20 years.

laut• 15 years ago

The batteries weigh a lot and require cooling. A Lotus Elise, which the Tesla Roadster is based on, weighs and costs less.

coryrc6• 15 years ago

The Nissan Leaf does not have battery cooling. Only the volatile type of Lithium batteries and NiMH batteries require cooling the first for life expectancy and safety and the latter because they are tremendously inefficient and give off large amounts of heat.

nickpinkston• 15 years ago

"it is puzzling to see why anyone should worry about potential shortages of neodymium and other rare-earths for alternative power and transport."

Well, I'm sure the military doesn't want to redesign everything that already uses them - we're broke enough as it is...

kwantam2• 15 years ago

The article incorrectly implies that the only way to make a synchronous machine is with a permanent magnet, and thus all synchronous machines have temperature issues. On the contrary, it is entirely possible to build synchronous machines with driven rotors (e.g., through slip rings) that have none of the temperature issues associated with using permanent magnets (it's the magnets themselves that are temperatures sensitive, not some intrinsic property of the synchronous machine design). They are more expensive to manufacture than the good old squirrel cage induction motor, but synchronous machines in general are more efficient over a wider range of output rotational rates than induction machines, have somewhat better failure modes, and are much easier to start up.

In many cases, it's cheaper to (try to) solve these problems with smart drive electronics, i.e., add additional complication to the cheap part of the system rather than to the expensive part. But for the highest output machines---multi-megawatt generators, for example---synchronous machines remain king.

There are some other fun things you can do with motor drive electronics. A lab mate of mine in grad school wrote a cool thesis on using the iron in an induction machine as an electric transformer in such a way that the motor drive and power converter could be controlled independently. In essence, in a Y-connected three-phase system, the motor is insensitive to 3rd harmonic content in the drive signal, so you can pass energy through the air gap in the 3rd harmonic and rectify it on the other side to turn your induction machine into the magnetics for a power converter.

http://dspace.mit.edu/handle/1721.1/28691

beambot• 15 years ago

That's a pretty cool inductive motor hack. Personally, my favorite esoteric motor has to be the wobble motor built using electropermanent magnets (essentially, programmable permanent magnets):

http://www.hizook.com/blog/2010/12/07/electropermanent-magne...

Do you know of any other "cool" motor hacks?

coryrc6• 15 years ago

Brusa has an induction motor with magnets embedded in the rotor. At high torque, the induction overrides the permanent magnets. At lighter loads, the permanent field dominates and turns it into a synchronous motor.

http://www.diyelectriccar.com/forums/showthread.php/evdl-syn...

amitraman1• 15 years ago

It's interesting how inventions from the early part of the 1900s are becoming more useful today. I remember reading an article which stated that engineers were re-discovering mathematical models from the early 1900s for use today.

The big concern I have is that we'll end up with more expensive hybrid cars and China will have the cost-effective stuff.

eru6• 15 years ago

Yes, re-using old inventions is important.

As another example: In the last 20 years there has been an explosion in the power of mathematical optimization, because numerics got fast and stable enough that algorithmic techniques that had been put into the bottom drawer decades ago have been resurrected. Those techniques were initially numerically unstable (or needed too much computation to keep them stable).

ck22• 15 years ago

Rare-earth elements are not actually that rare.

A few Canadian companies hold the rights to many of the resources in the USA.

For example there are some nice lithium sources in the USA but the Canadian companies will not mine them until there is a certain profitability level.

lutorm• 15 years ago

Lithium is an alkali metal, not a rare-earth element, so it's not such a good example.

PotatoEngineer• 15 years ago

I suspect that even if the resources were owned by US companies, they still wouldn't mine them, for exactly the same reason.

ck22• 15 years ago

Yes but it's an actual "homeland security" issue that we don't own the resources in our own country that are critical for our future infrastructure/transportation needs (vs. the theater issues at the airport).

turbofail2• 15 years ago

Another permanent-magnet-less motor design is the switched-reluctance motor. Its primary advantage over the induction motor is its dirt-simple rotor construction - it's essentially just a properly shaped chunk of iron, where an induction motor would require a copper squirrel-cage.

Its disadvantage relative to the induction motor is that it requires some cleverness in its controller and/or sensors in order to run at all. I actually wrote some control software for one as a side project - it was a somewhat frustrating experience (though a good portion of the frustration was due to malfunctioning hardware).

http://en.wikipedia.org/wiki/Switched_reluctance_motor

pjkundert• 15 years ago

Also interesting is their capability to produce their full Torque output at 0 RPM. For applications requiring high torque for "station keeping", this is crucial, and is pretty unique to SRM (Switched Reluctance Machine) motors.

I've been quite interested in repurposing the little Dyson "digital motor", but I suspect that a complete drive system redesign would be necessary to enable full variable RPM control (ie. 0-max, in both directions).

Question for turbofail: did your project happen to use the SRM motor from the Neptune front-load washers, or some other motor?

turbofail2• 15 years ago

It was a custom-made SRM made by someone else. They were intending to use it in an electric vehicle.

kragen6• 15 years ago

Very interesting! WP also says, "Stepper motors are similar to switched reluctance motors (which are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.)" I didn't know!

ChuckMcM• 15 years ago

Ah yes, AC motors, the bane of most of the EE's in my graduating class since computing electromagnetic fields in a rotating context was such old technology. At the time the only 'use' for them was machine tools and blower fans, both of which took advantage of the fact that you could plug them directly into a 3-phase power line and they would run at 60 RPM all day and all night.

Variable frequency 3-phase inverters which can support the current capacity to generate 100HP+ (75KW) was really only invented with iGBTs in the last couple of decades. The article doesn't mention that the inverters have to be cooled, as they are a significant source of heat as well.

kragen6• 15 years ago

I had no idea about IGBTs. Thanks!

http://en.wikipedia.org/wiki/Insulated-gate_bipolar_transist...

1053r• 15 years ago

The article incorrectly states that the Nissan Leaf needs a gearbox. In fact, it has a single reduction gear and an AC induction motor, just like the Tesla Roadster. (Well, ok, not as powerful...) As a Leaf owner, I can tell you it makes for a very interesting torque curve. From 0-30 it is VERY fast, from 30-60 it is pretty average, and from 60-90 it is dog slow acceleration.

eru6• 15 years ago

Which units are you using?

sbierwagen• 15 years ago

Leagues per hour, of course. Just like how I measure fuel consumption in rods per hogshead.

juiceandjuice2• 15 years ago

I think that a 350 mile range and 10 minute charge is ultimately the holy grail for electric cars. Most cars built try to shoot for 400 on highway gas mileage.

coryrc6• 15 years ago

EVs are better at everyday driving. You could make a house using a sawzall, but it will be better and faster to use a miter saw for most of the work and a sawzall for the odd chop while up on the roof.

ars• 15 years ago

10 minute charge is not possible with the current grid. You would need 1,500A service - just for the car (most homes have 200).

The cables would be as thick as your arm.

You can do battery swaps instead, but it requires an infrastructure build out first.

ajays• 15 years ago

Even a 1 hour recharge is not bad. After driving for 350 miles, I wouldn't mind stopping for a nice lunch. While you're having lunch, the car's batteries get recharged, for much less than the price of the lunch.

juiceandjuice2• 15 years ago

I never said the home would be the primary charge point, you wouldn't charge like this at home, but at a charge station.

I'm implying that these are the specs necessary for an electric car to truly be taken seriously as a replacement for a gas vehicle.

Furthermore, charging at a higher voltage, say even 720 volts (about twice the current roadster's voltage) gets you down to 500 amps to charge a Tesla in 10 minutes, which is manageable for cables. Charge stations could have a reserve/buffered system they can charge from that way they wouldn't be hitting the grid all at once if 5-6 cars show up. You could do a similar thing at your house (basically a large UPS)

The battery swap thing is a pipe dream, IMO.

hugh3• 15 years ago

I'd be more interested in having a 100-mile range and an onboard gas-powered generator to give me effectively-unlimited range when I'm road-tripping and damn-near-free trips when I'm commuting.

d23• 15 years ago

I drive a 2001 Ford F350. I get dirty looks from Prius drivers every day. Little do they know (and the econ article mentions this) that their little buzzbombs contain 2.2 pounds of neodymium which is both radioactive and massively damages the environment in its production and disposal.

I bought my truck used. I bought it with 150k miles on it and I plan to put on another 400k miles before it goes to the big diesel garage in the sky. These f'ing Prius yuppies buy a car every 2 years thinking that saving a few gallons of gas is going to save the planet. Try saving the environmental cost of producing that horrible pile of radioactive and chemical garbage by buying a 10 year old used car and driving it for the next decade.

Edit: And buy American darnit!

kragen6• 15 years ago

How radioactive is neodymium? It looks like most of its isotopes are stable and the rest have half-lives significantly exceeding the current age of the universe, just like ²³⁸U.

d23• 15 years ago

PBS video on rare earth mining in China, specifically mentioning the Prius engine and battery e.g. the battery contains 22 pounds (10 kg's) of lanthanum.

http://www.youtube.com/watch?v=JL4fluj004o

coryrc6• 15 years ago

You sure beat up that strawman pretty well. Good thing no chemicals are used in making fuel or in the production of your F350. And nobody is driving older Prii, you'll have to tell some of my customers they don't actually exist.

bmelton2• 15 years ago

The metal harvested for your frame is also harmful to the environment in its manufacture and production.

This ultimately gets back to the allegation that the dust-to-dust cost of a Prius is less eco-friendly than that of a HumVee, which is a meme that was running around few years ago, and which was ultimately debunked based on a number of faulty assumptions, some of which you make in your argument.

- There is no resale market for Prii

- A Prius won't last as long as a more standardly built vehicle

- The Prius uses an extraordinarily large amount of nickel, which is toxic and/or unrecoverable.

As I said, these were ultimately proven false enough that no informed person can seriously believe that a gas guzzling Hummer is better for the environment. I'd wager the same argument holds true for an F150 as well.

As for the presence of radiation in neodymium, you probably have the same amount of radiation in your alternator, only your alternator isn't shielded, as it is in Prius batteries. Pepto Bismol is also radioactive, and has a half-life longer than the age of the universe -- it doesn't necessarily imply that it's unsafe.

Also, please, let's try to keep the drama down, pretty please? There is a great deal of rhetoric and emotion in your post that needn't be there.

d23• 15 years ago

I never made any of the allegation's in your bullets. The simple fact is that producing a Prius is bad for the environment and buying a new one every few years is a hell of a lot worse for the environment than buying a 10 year old vehicle and driving it another decade.

That, along with an ignorance for the environmental impact of the materials used in a Prius was my point.

Also, please, let's try to keep the drama down, pretty please? There is a great deal of rhetoric and emotion in your post that needn't be there.

VomisaCaasi• 15 years ago

This happened yesterday:

American mining company Molycorp has bought up a 90.023 share in Estonia's rare earth metals producer AS Silmet, taking control of one of very few sources of the much-sought materials outside China.

http://news.err.ee/economy/c12a9355-2b41-46d3-b00e-875806144...

Relevant, I hope.

On Tesla's induction motor

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