Rare earth magnets are just too good for electric motors to go this way. Europe and the US just need to get the rare earth manufacturing going and stop being reliant on china for this stuff.
A historical pioneer in the complex technology of electric motors without magnets
Those who know the history of electric machines will find the title and verbiage very amusing. Motors with no permanent magnets were the first practical ones, and at this point wound-rotor motors are over a century old.
It's worth noting that some of the biggest motors have always been designed this way, because the size of magnets required would make them both too expensive and dangerous, and still not powerful enough for their size; a field coil can generate a field that's only limited by the current and resistive heating of the winding, but rare earth magnets have fixed limits on field strength.
Long ago, when I was in Cub Scouts, one of the projects was to build an electric motor. The parts list was:
1. a plank to form the base
2. several 6 inch nails
3. wire
4. a tin can (as a source of sheet metal)
5. tape
No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in.
A loud vibration ensued, and then it burst into flames. My mom wasn't happy.
P.S. I still use tin cans as a source of sheet metal. There was a big storm a while ago, with tree branches whistling by at high speed. (Not a good time to be outside.)
Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing.
I've used coke can metal for shingles and flashing, too. They don't rust.
The Cub Scouts in the 1960s were a lot of fun. Each den meeting involved a project. The other one I remember was we each built a kite from scratch.
Mine was a bit fragile, and the first gust of wind shredded the sticks and plastic film.
But it was still fun!
As a teen I built a flame thrower. No, I'm not going to explain how to build one. My dad told me that God looks out for little boys, because otherwise they'd never survive to adulthood.
When I was 9, I found a book of his "Rocket Manual for Amateurs". The opening sentence was something like "if you're fascinated by things that burn and explode, this book is not for you." Who could resist a teaser like that? I promptly read it cover to cover. He wouldn't let me buy any of the necessary materials.
All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient.
In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.
A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement.
Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field.
This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency.
You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
You can also make squirrel-cage rotors that are auto-inductive in the sense that they resist slip from the rotating field of the stator. This is also extremely simple to manufacture and doesn't require driving separate fields or anything similar.
It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
The actual alternative is induction motors, which are just a bit less efficient than PMSM and otherwise basically the same. Except that the frequency fed to them isn't exactly proportional to speed.
They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
Not quite true: you're also limited by the mechanical strength of your windings and core (this is the upper limit on superconducting magnets like at CERN and in fusion plants).
BMW also makes rare-earths-free motors for their EVs and - at this very moment - theirs are far more advanced. They offer almost twice the power (up to 300kW vs 160kW) and are on a 800v architecture.
If you take care of the car it’s just brake pads, tires, rotors. Pads and rotors are really simple to DIY. Tires are more expensive than like… an Elantra, but if you’re buying a 60k car you can afford 1.2k in tires… otherwise don’t buy the car.
If you get into an accident or let the bmw get into disrepair via neglect, yeah it’s not cheap to clean up. Body work is expensive on any car though, and I don’t have sympathy for people who own higher-end cars and don’t take care of them, they deserve to pay the price for it.
It's more than that though. Any repairs due to wear and tear or whatever, ends up being really expensive. Although you can probably reduce the costs a bit if you get the non-branded OEM part or potentially the same part from another manufacturer (e.g. the toyota supra uses a lot of bmw parts so if the toyota part might be cheaper than the same bmw part).
That was my whole point actually, the wear and tear is really minimal if you get regular oil changes. Things don’t just break and need replacing. Tires, rotors, brakes, those wear out. The tires are not cheap, rotors and pads aren’t crazy expensive and super easy to DIY.
The cheapest Minis are made by GWM in China, and are using different motors and batteries.
However, comparing prices between cars nowadays is a complicated matter. BMW's iX1 and iX2 (they use the BMW EESM motors) theoretically cost about €55k, but they have been very recently available to lease for about €250 euro per month - so pretty much for the same price as the cheapest electric Renault if leased.
They share the same OEMs, and both are following the same ex-China automotive strategy.
Renault has also been thumbing China recently for undermining EU manufacturing as well [0] while China has returned to using Wolf Warrior diplomacy against Europe [1][2][3][4] using the same rhetoric that the Trump admin uses.
Of course, under the Xi admin China's foreign policy has always viewed the EU as inferior and a has-been [5] and has become an active participant in the Ukraine War [6][7].
Europe might not be able to trust the US, but it can't trust China either.
Which is quite the contrast to Mercedes new axial flux electric motor, which goes all in on rare earths- the design relies on the highest end high-grade permanent magnets.
Still, presumably Mercedes ambitions are for few motors than BMW or Renault.
Vastly different target market and/or features there. Mercedes are chasing maximum power density, minimum weight for high performance deployments, with seemingly little concern for cost or supply chain.
Renault is going after the consumer market with these motors, where minimising cost and maximising availability is more important than pushing past 95% efficiency or cramming a 700kW power output in a motor that is small and light enough to fit inside of a wheel hub.
It's interesting that this is a brushed design. In the RC car community, brushless motors are generally regarded as superior, but those of course have the rare earth magnet problem.
Technically the brushes can wear out, although there are claims they are good for 150,000-250,000 miles it seems.
It's technically not a brush but a slip-ring. The design of these motors is very similar to automotive alternators, just scaled up 100x (in terms of power).
yeah I misspoke, I meant to say that it's a brush riding on a slip-ring (continuous contact, no arcing, lasts long) rather than a bunch of contacts in a cylinder (commutator, arcing, wears out).
Because it's the discontinuities in the commutator where the sparks fly (with much help from self-induction of the motor's coils) and erode the ring and brushes.
"Brushless DC motors" are good because brushed DC motors are constantly switching polarity, which causes arcing of the brushes, which causes wear. The brushes are not there to energize the rotor; the rotor is just magnets after all. The brushes are there to tell the stator to change polarity.
Brushless DC motors don't arc -- because they switch stator polarity with electronics that sense the position of the rotor without rubbing parts. (They can also fine-tune the stator current spikes to make the motor very efficient over a wide speed range, which brushed DC motors cannot do.) The lack of arcing is more important than the fact that they don't have rotating contact points.
Brushed AC motors have rotating contact points (slip rings) but they don't arc (ideally), so the contact points don't degrade as fast as brushed DC motors do. But they do carry a lot of current because their purpose is to energize the rotor. Brushed AC motors are not ideal, but making an AC motor "brushless" is not nearly as big a win as making a DC motor brushless.
Wait. You're saying DC motors require current that's constantly switching polarity? So they're sort of really AC internally?
Yep. All motors require constantly changing current. The distinction between AC and DC motors is whether you feed the motor externally with current that is already alternating sinusoidally, or whether the motor itself turns external DC into some kind of AC.
Rare earth magnet motors require software too if you want them to be maximally efficient. You could embody that software in e.g. an FPGA of course, but it's still software.
Could be wrong, but AFAIK the CATL Sodium batteries haven't yet hit LFP pricing.
You are unlikely to see a vehicle with sodium batteries until after that happens, and it needs to be significantly less than LFPs as you Na batteries have more weight per Wh. I believe they also have a shorter lifespan (but not NMC short). Edit correction, looks like CATL is promising 15000 cycles, which is much longer than LFPs which usually come in at 7000 to 10000.
It seems far more likely to me that if the Na prices tank, you'll probably first see them deployed as grid and home battery solutions.
The energy density of LFP batteries are also 30-50% higher than sodium based battery chemistries. Even if sodium battery prices drop, the lower energy density is a big disadvantage. My understanding is that sodium batteries are aimed at stationary use-cases, like battery buffers for fast charging.
At the cell level yes. But at the pack level, you need less/no cooling and there is virtually no risk of runaway fires. This means the cells can be packed more densely and you get some weight benefits for all the stuff you no longer need for fire safety.
CATL already put sodium ion in cheap cars. And there are other benefits to this type of battery like a wider range of operating temperatures that cover essentially all of the extreme temperatures you'd find in the arctic and the hottest deserts.
I would not be surprised to find some of these batteries in big semis a few years down the line when the cost benefits make the space/weight sacrifices worth the trade off.
But you are right that domestic and grid storage are also going to be huge use cases.
And high temperatures, too. Meaning they don't require cooling nor heating, basically matching the per kg capacity of ready modules with LFP while being significantly safer and less complex.
They're promising to start selling a Qiyuan A06 variant with Sodium batteries sometime this year... so if you went looking you could probably see one... or will be able to soon.
EESMs are primarily manufactured by European OEMs (ZF, MAHLE, Schaffler, AEM) and their Indian JV partners (Sona Comstar, Sterling, and the India branches of the OEMs listed). Both have been blocked via export controls from accessing battery tech from China over the past few years, and a major reason for the push for EESMs was for an ex-China supply chain, especially after China began export controlling rare earths to the EU [6].
Additonally, Chinese and American EVs tend to use PMSMs unlike European and now Indian EVs. Also, the EU is cracking down on automotive exports (cars and OEMs) from non-FTA states as part of the EU Industrial Accelerator Act (which btw has made China go ballistic [2][3][4][5]).
On the other hand, they will most likely use Japanese or Korean solid-state batteries as Idemetsu Kosan is in the process of mass producing them [0][1] as is LG [7], and both Japan+SK are FTA partners with the EU.
Electrically excited synchronous machines (EESMs), also known as wound field synchronous machines (WFSMs) have a number of potential advantages and disadvantages compared to interior permanent magnet synchronous machines (IPMSMs). IPMSMs are the dominant motor topology currently in use for North American electric vehicles.
Advantages:
- Not subject to the price and supply chain volatility of rare earth permanent magnets.
- For highway dominant drive cycles, the cycle efficiency of EESMs can be higher than state of the art IPMSMs. EESMs tend to have their best efficiency at moderate torques and high speeds because of their excellent field weakening characteristics. I tend to think that they would be a good fit for application in class 8 trucks or as auxiliary motors in automobiles with two powered axles.
- The output torque doesn't necessarily decrease with rotor temperature. In IPMSMs the permanent magnet flux linkage decreases with rotor temperature.
- At least theoretically, with proper control, it is possible to operate EESMs with unity power factor and decrease the kVA rating of the stator inverter.
- If there is a stator inverter fault, there are schemes to denergize the rotor which have some safety implications.
Disadvantages:
- DC current needs to be transferred to the rotating field winding. For automotive applications this tends to be done either with brushes and slip rings or brushlessly using a high frequency transformer with a rotating rectifier. In either case additional power electronics and other components are needed for the field power transfer and control which reduces some of the potential cost savings of the elimination of the permanent magnets. If brushes and slip rings are used with oil spray/oil jet cooling of the rotor they need to be sealed in a separate compartment. I am a little surprised that Renault has stuck with brushes and slip rings versus an inductive high frequency transformer solution. I think this has limited their power density.
- For very torque dense machines, cooling the rotor field winding is challenging, and in my opinion is best accomplished by oil spray/oil jet cooling.
- It is difficult to reach the same maximum speeds as IPMSMs in an automotive package size. The rotor field winding retention system to keep the field turns from moving into the airgap at high speeds needs considerable attention during the design.
- The overall axial length of the non-active region of EESMs is typically longer than IPMSMs because of the field winding end turns and field excitation system.
- EESM efficiency is dominated by the manufacturable slot fill of the field winding.
- High performance current/torque regulation is considerably more difficult.
High performance EESMs have been used in aerospace generator applications for decades, albeit with a different rotor excitation system than what is used in automotive applications. Renault (and their supplier Continental) really led the commercialization of EESMs into automotive mass production. Now BMW has followed suit and multiple suppliers have EESM designs (Mahle, ZF, etc.) GM had a really nice EESM design and high frequency transformer excitation which they published back in 2014. My colleagues and I built several generations of EESMs as part of U.S. Dept. of Energy projects (https://www.osti.gov/servlets/purl/1837809) and I think they have their place as EV traction motors for certain applications.
Weren't Tesla ACIM drive unit motors before Model 3 also magnet-free? I thought they used passive isolated bundles of copper wires and their reluctance as magnets.
It was a dude with motors on a table with a flip board. No animations. No diagrams. When it got to the point about having one of each motor, and using the best, he then said that you use the permanent motor even when the other makes sense. Ok, well then why have the two different kinds of motors? No answer. Just handwaved. If you can't use the induction motor when its most efficient, because thats when the permanent motor is causing spin loss, why have the induction motor at all? No answer.
So. Analog presentation. Actual motors on a desk with a flip chart. No animations. No internal visualizations. One page had diagrams that would have been better super-imposed (or hey, animated). Then one page the begs questions with no answers given.
They're also used by Nissan [1], BMW [2], and Indian EVs [3].
European firms like ZF, Valeo, MAHLE, and Schaffler along with British firms like AEM have been working with their Indian JVs as well as Indian players like Sona Comstar and Sterling for a couple years now to integrate supply chains for mass-producing EESMs.
EESMs as well as the larger OEM story played a role in helping land the EU-India and the UK-India FTAs because the supply chains for French+Italian (Renault, Stellantis), Japanese (Toyota, Honda, Suzuki), Korean (Hyundai-Kia), and Indian automotive manufacturers merged.
On the other hand, EESM EVs aren't a thing here in North America nor China yet as both primarily use PMSMs (edited typo).
> does Nissan still use these motors, the car in the linked article has been discontinued
Yes. The Ariya was discontinued in North America (EDIT: USA, TIL still sold in Canada) but is still manufactured and sold in Asia.
> European and Indian manufacturers/engineering are definitely not in the same category though
It's the same manufacturers and supply chain now.
Renault and their OEMs are the biggest driver for EESM, and Renault's largest markets and manufacturing hubs are France, India, and Romania. Heck, Renault is now going to start exporting it's Made in India cars and parts back to the EU [0] becuase of the EU-India FTA.
And the European OEMs have transferred the IP for EESMs to Indian JVs as I mentioned. It's the same style of tech transfer as Samsung did for BYD and TDK for CATL for battery chemistry in the 2000s. Heck, Valeo [1], MAHLE [2], ZF [3], and Schaffler [4] are opening and expanding factories and R&D hubs dedicated to EV transmission manufacturing in India for domestic and export usecases.
Also, if you've ever driven a Japanese (Toyota, Honda, Suzuki) or Korean (Hyundai, Kia) make care in the EU, Australia, Middle East, Africa, or Asia outside of their home countries their parts sourcing and even the entire manufactured car would have come from India, such as the Toyota Urban Cruiser EV [5].
No, and it was mentioned by the consortium of European cars manufacturers after the joint press release with Der Leyen herself: the implementation of factories and research centers in India is solely to be able to sell on that market. It is the exact same process that happened with China in the past. The exact same also happened with Airbus.
You are also wrong on the market importance for Renault. For 2024, France was the biggest, followed by Italy, Turkey, Spain, Germany, Brazil, UK, Morocco, BENELUX, Romania, Poland, Netherlands and... #13 India with 0.9% market share...
Supply chains didn't change at all, in fact it did the opposite, and Europeans won't rely on anything Indian made for the near future, as local re-industrialization is already acted on and even accelerated since the pandemic.
Production numbers across all manufacturers even Volkswagen (which was unexpected) show the number of cars manufactured in Europe increased in the past 2 years.
Electric cars in Europe mostly come from China, the US and European brands. Nothing Indian-made, not even parts.
Not sure why this was voted down, it was the most useful comment here.
does Nissan still use these motors, the car in the linked article has been discontinued, and then only real info I can find on their site about the leaf is about their ROCKIN' bose sound system/s
Not just some, approximately all of them. It greatly complicates the logistics of a black start. † Of course that situation has additional complexity due to the need for substantial additional power in order for the various fuel supply systems to operate but I digress.
After watching a Munro video about it, I see your point. In the motor shown, the rotor gets its magnetic field simply by inducing a current and a field in it in reaction to the stator's field. There are no electromagnets in the rotor like I expected. In that case, I'm not sure either... I'd say more likely than not but it's complicated since the stator basically needs to induce a field and at the same time recover energy from the field that comes back from the rotor. I would further guess that the phase shift between the two components makes it possible to treat them separately.
Previous comment: Don't see why not - the "field" coils (the ones that replace the permanent magnets) need to be energized, which can initially come from the batteries if necessary.
There is something... weird about this. this tech has existed.... a long time. And I am not familiar with what is common in electric cars so may be missing something obvious but thought this was already how it was done. let me explain my limited understanding.
With ac motors electromagnets can be used in the rotor. there is even a super clever way to do it where the electromagnet in the rotor is driven wirelessly via induction. there are some downsides but having no physical sliding electrical connection to the rotor is a huge upside. The ac can be dynamically formed from DC via high speed switching(transistors, in industry often called a VFD).
Due to the upsides of ac induction motors I sort of assumed this was already what was found in cars. I am a bit surprised to find out there were rare earth magnets in the first place.
Permanent magnet motors are simpler and cheaper to make, at least in the small (yes, small --- there are electric motors in the MW range in industrial applications, which are themselves larger than an average car) sizes found in EVs.
AC motors are not magic. The core is essentially just a coil with one turn, so it can generate only a very limited magnetic field. So they have to be bulkier for a given power density and generally slightly less efficient.
I don't think car owners have to worry about this the first half million miles or so with these motors. Electrical motors last a long time. We'll know for sure in a few decades, I guess. That's how long it will take for a significant number of their cars to actually drive that far.
Also, compare this to ICE engines which experience continuous explosions, lots of mechanical parts, extreme temperature swings, etc. and still manage pretty decent durability. There's simply no base for assuming that parts like this wearing out and needing to be replaced is going to be a common thing.
The Continental and Renault motors like those in my Kangoo ZE and Zoe have so far proven fairly reliable, with the occasional exception being shaft bearings. The Q210 is particularly robust. I'm not aware of anybody having brush/slip ring issues yet.
Cars already have lots of wear items and a mature service industry for them. If I can reliably get at least 50k miles out of it, then I wouldn't be all that bothered, as this is not likely to be an expensive part or service.
The main difference between this and your typical AC induction motors (also magnet free) is that this is a DC motor so you need a commutator. Your AC induction magnet free motors are very similar to drone motors in that you don't have any electrically active moving parts like slip rings and commutators. But for AC induction there will be a slight lag (known as slip).
Rare earth magnets are just too good for electric motors to go this way. Europe and the US just need to get the rare earth manufacturing going and stop being reliant on china for this stuff.
A historical pioneer in the complex technology of electric motors without magnets
Those who know the history of electric machines will find the title and verbiage very amusing. Motors with no permanent magnets were the first practical ones, and at this point wound-rotor motors are over a century old.
It's worth noting that some of the biggest motors have always been designed this way, because the size of magnets required would make them both too expensive and dangerous, and still not powerful enough for their size; a field coil can generate a field that's only limited by the current and resistive heating of the winding, but rare earth magnets have fixed limits on field strength.
Long ago, when I was in Cub Scouts, one of the projects was to build an electric motor. The parts list was:
1. a plank to form the base
2. several 6 inch nails
3. wire
4. a tin can (as a source of sheet metal)
5. tape
No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in.
A loud vibration ensued, and then it burst into flames. My mom wasn't happy.
P.S. I still use tin cans as a source of sheet metal. There was a big storm a while ago, with tree branches whistling by at high speed. (Not a good time to be outside.)
Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing.
I've used coke can metal for shingles and flashing, too. They don't rust.
there's also a plastic liner on them that I'm sure helps.
It also helps that they are made from aluminum which doesn’t rust like iron does.
Been there. Im gonna guess that 90% of HN folk have similar stories to tell.
The Cub Scouts in the 1960s were a lot of fun. Each den meeting involved a project. The other one I remember was we each built a kite from scratch.
Mine was a bit fragile, and the first gust of wind shredded the sticks and plastic film.
But it was still fun!
As a teen I built a flame thrower. No, I'm not going to explain how to build one. My dad told me that God looks out for little boys, because otherwise they'd never survive to adulthood.
When I was 9, I found a book of his "Rocket Manual for Amateurs". The opening sentence was something like "if you're fascinated by things that burn and explode, this book is not for you." Who could resist a teaser like that? I promptly read it cover to cover. He wouldn't let me buy any of the necessary materials.
You're right about the verbiage being amusing.
All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient.
In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.
What advantage do permanent magnets provide that it isn't the case that all motors are made without them?
A lack of wear components.
A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement.
Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field.
This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency.
You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
You can also make squirrel-cage rotors that are auto-inductive in the sense that they resist slip from the rotating field of the stator. This is also extremely simple to manufacture and doesn't require driving separate fields or anything similar.
To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
It’s a near-doubling of energy loss - probably a healthier way to understand it when the efficiencies are all 90%+
Funnily enough if enough of that energy loss (heat) can be scavange, this wouldn't be nearly that bad for us living up here in the cold.
You can get about 2/3 as much output power for a given amount of waste heat and cooling capacity.
It's like how laptop power bricks used to be big and get hot, and now they aren't and don't.
It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
The actual alternative is induction motors, which are just a bit less efficient than PMSM and otherwise basically the same. Except that the frequency fed to them isn't exactly proportional to speed.
They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
Not quite true: you're also limited by the mechanical strength of your windings and core (this is the upper limit on superconducting magnets like at CERN and in fusion plants).
And if you also ignore iron saturation.
I own a Zoe for that reason
BMW also makes rare-earths-free motors for their EVs and - at this very moment - theirs are far more advanced. They offer almost twice the power (up to 300kW vs 160kW) and are on a 800v architecture.
The cheapest EV model Renault sells is around €20K, the cheapest BMW EV is around €65K.
It's safe to say the companies are not in the market bracket, no?
The bit the gets me more than the sale price is servicing.
BMWs have a terrible record for needing expensive repairs.
I know you shouldn’t rely on anecdote, but it seems I do.
The only way I would buy a BMW is if it were an EV. I’m just not brave (or rich) enough to buy their ICEs.
If you take care of the car it’s just brake pads, tires, rotors. Pads and rotors are really simple to DIY. Tires are more expensive than like… an Elantra, but if you’re buying a 60k car you can afford 1.2k in tires… otherwise don’t buy the car.
If you get into an accident or let the bmw get into disrepair via neglect, yeah it’s not cheap to clean up. Body work is expensive on any car though, and I don’t have sympathy for people who own higher-end cars and don’t take care of them, they deserve to pay the price for it.
It's more than that though. Any repairs due to wear and tear or whatever, ends up being really expensive. Although you can probably reduce the costs a bit if you get the non-branded OEM part or potentially the same part from another manufacturer (e.g. the toyota supra uses a lot of bmw parts so if the toyota part might be cheaper than the same bmw part).
That was my whole point actually, the wear and tear is really minimal if you get regular oil changes. Things don’t just break and need replacing. Tires, rotors, brakes, those wear out. The tires are not cheap, rotors and pads aren’t crazy expensive and super easy to DIY.
What other wear and tear things are expensive?
After 22 years, my z4 has needed batteries and a starter.
Recently, there was a problem with the engine misfiring but it was $200.
LA, California
It's still good to know that SOTA is further, and we can expect the more advanced designs to seep into more affordable segments.
BMW also produces Mini EVs, which start at £26,840
The cheapest Minis are made by GWM in China, and are using different motors and batteries.
However, comparing prices between cars nowadays is a complicated matter. BMW's iX1 and iX2 (they use the BMW EESM motors) theoretically cost about €55k, but they have been very recently available to lease for about €250 euro per month - so pretty much for the same price as the cheapest electric Renault if leased.
They share the same OEMs, and both are following the same ex-China automotive strategy.
Renault has also been thumbing China recently for undermining EU manufacturing as well [0] while China has returned to using Wolf Warrior diplomacy against Europe [1][2][3][4] using the same rhetoric that the Trump admin uses.
Of course, under the Xi admin China's foreign policy has always viewed the EU as inferior and a has-been [5] and has become an active participant in the Ukraine War [6][7].
Europe might not be able to trust the US, but it can't trust China either.
[0] - https://www.reuters.com/world/china/renault-ceo-asks-eu-enco...
[1] - https://www.globaltimes.cn/page/202605/1361926.shtml
[2] - https://www.chinausfocus.com/finance-economy/dear-brussels-d...
[3] - https://www.globaltimes.cn/page/202605/1362161.shtml
[4] - http://news.china.com.cn/2026-06/10/content_118541873.shtml
[5] - https://fddi.fudan.edu.cn/_t2515/57/f8/c21257a743416/page.ht...
[6] - https://www.reuters.com/business/aerospace-defense/russians-...
[7] - https://www.pravda.com.ua/eng/news/2026/06/12/8039041/
same order of magnitude :)
Which is quite the contrast to Mercedes new axial flux electric motor, which goes all in on rare earths- the design relies on the highest end high-grade permanent magnets.
Still, presumably Mercedes ambitions are for few motors than BMW or Renault.
Vastly different target market and/or features there. Mercedes are chasing maximum power density, minimum weight for high performance deployments, with seemingly little concern for cost or supply chain.
Renault is going after the consumer market with these motors, where minimising cost and maximising availability is more important than pushing past 95% efficiency or cramming a 700kW power output in a motor that is small and light enough to fit inside of a wheel hub.
It's interesting that this is a brushed design. In the RC car community, brushless motors are generally regarded as superior, but those of course have the rare earth magnet problem.
Technically the brushes can wear out, although there are claims they are good for 150,000-250,000 miles it seems.
It's technically not a brush but a slip-ring. The design of these motors is very similar to automotive alternators, just scaled up 100x (in terms of power).
I've probably taken apart 10 automotive alternators. Every single one had brushes.
yeah I misspoke, I meant to say that it's a brush riding on a slip-ring (continuous contact, no arcing, lasts long) rather than a bunch of contacts in a cylinder (commutator, arcing, wears out).
Slip rings have brushes.
Yes but they wear less than DC brushed motors exactly because it's a slip ring and not a commutator
Because it's the discontinuities in the commutator where the sparks fly (with much help from self-induction of the motor's coils) and erode the ring and brushes.
"Brushless DC motors" are good because brushed DC motors are constantly switching polarity, which causes arcing of the brushes, which causes wear. The brushes are not there to energize the rotor; the rotor is just magnets after all. The brushes are there to tell the stator to change polarity.
Brushless DC motors don't arc -- because they switch stator polarity with electronics that sense the position of the rotor without rubbing parts. (They can also fine-tune the stator current spikes to make the motor very efficient over a wide speed range, which brushed DC motors cannot do.) The lack of arcing is more important than the fact that they don't have rotating contact points.
Brushed AC motors have rotating contact points (slip rings) but they don't arc (ideally), so the contact points don't degrade as fast as brushed DC motors do. But they do carry a lot of current because their purpose is to energize the rotor. Brushed AC motors are not ideal, but making an AC motor "brushless" is not nearly as big a win as making a DC motor brushless.
Wait. You're saying DC motors require current that's constantly switching polarity? So they're sort of really AC internally?
Yep. All motors require constantly changing current. The distinction between AC and DC motors is whether you feed the motor externally with current that is already alternating sinusoidally, or whether the motor itself turns external DC into some kind of AC.
"Replace the magnet with a controllable magnet" is probably the most automotive-engineering sentence possible.
Also known as: “we removed the rare earths and added software.”
Synchronous motors: running on software since the 1880s. Nikola really was ahead of his time!
He invented the induction motor which runs right off the grid.
Rare earth magnet motors require software too if you want them to be maximally efficient. You could embody that software in e.g. an FPGA of course, but it's still software.
"At the same time, China is also the world's leading producer of electric cars..."
Kind of interesting for a professionally branded company to use "..." like that
How soon to see rare-earth-free paired with CATL Sodium batteries? Seems a price war, range war is imminent.
Could be wrong, but AFAIK the CATL Sodium batteries haven't yet hit LFP pricing.
You are unlikely to see a vehicle with sodium batteries until after that happens, and it needs to be significantly less than LFPs as you Na batteries have more weight per Wh. I believe they also have a shorter lifespan (but not NMC short). Edit correction, looks like CATL is promising 15000 cycles, which is much longer than LFPs which usually come in at 7000 to 10000.
It seems far more likely to me that if the Na prices tank, you'll probably first see them deployed as grid and home battery solutions.
The energy density of LFP batteries are also 30-50% higher than sodium based battery chemistries. Even if sodium battery prices drop, the lower energy density is a big disadvantage. My understanding is that sodium batteries are aimed at stationary use-cases, like battery buffers for fast charging.
At the cell level yes. But at the pack level, you need less/no cooling and there is virtually no risk of runaway fires. This means the cells can be packed more densely and you get some weight benefits for all the stuff you no longer need for fire safety.
CATL already put sodium ion in cheap cars. And there are other benefits to this type of battery like a wider range of operating temperatures that cover essentially all of the extreme temperatures you'd find in the arctic and the hottest deserts.
I would not be surprised to find some of these batteries in big semis a few years down the line when the cost benefits make the space/weight sacrifices worth the trade off.
But you are right that domestic and grid storage are also going to be huge use cases.
One of the most interesting features of sodium batteries is that they still perform good in cold temperatures.
And high temperatures, too. Meaning they don't require cooling nor heating, basically matching the per kg capacity of ready modules with LFP while being significantly safer and less complex.
They're promising to start selling a Qiyuan A06 variant with Sodium batteries sometime this year... so if you went looking you could probably see one... or will be able to soon.
Looks ideal for a power wall at home.
Superior temperature range in cold weather as well IIRC.
Unlikely.
EESMs are primarily manufactured by European OEMs (ZF, MAHLE, Schaffler, AEM) and their Indian JV partners (Sona Comstar, Sterling, and the India branches of the OEMs listed). Both have been blocked via export controls from accessing battery tech from China over the past few years, and a major reason for the push for EESMs was for an ex-China supply chain, especially after China began export controlling rare earths to the EU [6].
Additonally, Chinese and American EVs tend to use PMSMs unlike European and now Indian EVs. Also, the EU is cracking down on automotive exports (cars and OEMs) from non-FTA states as part of the EU Industrial Accelerator Act (which btw has made China go ballistic [2][3][4][5]).
On the other hand, they will most likely use Japanese or Korean solid-state batteries as Idemetsu Kosan is in the process of mass producing them [0][1] as is LG [7], and both Japan+SK are FTA partners with the EU.
[0] - https://www.chiyodacorp.com/en/projects/solidelectrolytefaci...
[1] - https://battery-tech.net/battery-markets-news/idemitsu-kosan...
[2] - https://www.globaltimes.cn/page/202605/1361926.shtml
[3] - https://www.globaltimes.cn/page/202605/1362200.shtml
[4] - https://www.globaltimes.cn/page/202605/1362161.shtml
[5] - https://www.ft.com/content/5903318c-319b-426e-b05d-062f7620f...
[6] - https://www.reuters.com/world/china/eu-lawmakers-rebuke-chin...
[7] - https://blog.lgchem.com/en/2026/03/25_solid_state_battery/
Electrically excited synchronous machines (EESMs), also known as wound field synchronous machines (WFSMs) have a number of potential advantages and disadvantages compared to interior permanent magnet synchronous machines (IPMSMs). IPMSMs are the dominant motor topology currently in use for North American electric vehicles.
Advantages:
- Not subject to the price and supply chain volatility of rare earth permanent magnets.
- For highway dominant drive cycles, the cycle efficiency of EESMs can be higher than state of the art IPMSMs. EESMs tend to have their best efficiency at moderate torques and high speeds because of their excellent field weakening characteristics. I tend to think that they would be a good fit for application in class 8 trucks or as auxiliary motors in automobiles with two powered axles.
- The output torque doesn't necessarily decrease with rotor temperature. In IPMSMs the permanent magnet flux linkage decreases with rotor temperature.
- At least theoretically, with proper control, it is possible to operate EESMs with unity power factor and decrease the kVA rating of the stator inverter.
- If there is a stator inverter fault, there are schemes to denergize the rotor which have some safety implications.
Disadvantages:
- DC current needs to be transferred to the rotating field winding. For automotive applications this tends to be done either with brushes and slip rings or brushlessly using a high frequency transformer with a rotating rectifier. In either case additional power electronics and other components are needed for the field power transfer and control which reduces some of the potential cost savings of the elimination of the permanent magnets. If brushes and slip rings are used with oil spray/oil jet cooling of the rotor they need to be sealed in a separate compartment. I am a little surprised that Renault has stuck with brushes and slip rings versus an inductive high frequency transformer solution. I think this has limited their power density.
- For very torque dense machines, cooling the rotor field winding is challenging, and in my opinion is best accomplished by oil spray/oil jet cooling.
- It is difficult to reach the same maximum speeds as IPMSMs in an automotive package size. The rotor field winding retention system to keep the field turns from moving into the airgap at high speeds needs considerable attention during the design.
- The overall axial length of the non-active region of EESMs is typically longer than IPMSMs because of the field winding end turns and field excitation system.
- EESM efficiency is dominated by the manufacturable slot fill of the field winding.
- High performance current/torque regulation is considerably more difficult.
High performance EESMs have been used in aerospace generator applications for decades, albeit with a different rotor excitation system than what is used in automotive applications. Renault (and their supplier Continental) really led the commercialization of EESMs into automotive mass production. Now BMW has followed suit and multiple suppliers have EESM designs (Mahle, ZF, etc.) GM had a really nice EESM design and high frequency transformer excitation which they published back in 2014. My colleagues and I built several generations of EESMs as part of U.S. Dept. of Energy projects (https://www.osti.gov/servlets/purl/1837809) and I think they have their place as EV traction motors for certain applications.
Weren't Tesla ACIM drive unit motors before Model 3 also magnet-free? I thought they used passive isolated bundles of copper wires and their reluctance as magnets.
https://youtu.be/FHufjrP0xDI?is=xmFQrXGa1dBHM67I
This is a helpful explanation of what this technology is and looks like. (Munro)
It was a dude with motors on a table with a flip board. No animations. No diagrams. When it got to the point about having one of each motor, and using the best, he then said that you use the permanent motor even when the other makes sense. Ok, well then why have the two different kinds of motors? No answer. Just handwaved. If you can't use the induction motor when its most efficient, because thats when the permanent motor is causing spin loss, why have the induction motor at all? No answer.
So. Analog presentation. Actual motors on a desk with a flip chart. No animations. No internal visualizations. One page had diagrams that would have been better super-imposed (or hey, animated). Then one page the begs questions with no answers given.
Mentioned in another HN thread [0]:
They're also used by Nissan [1], BMW [2], and Indian EVs [3].
European firms like ZF, Valeo, MAHLE, and Schaffler along with British firms like AEM have been working with their Indian JVs as well as Indian players like Sona Comstar and Sterling for a couple years now to integrate supply chains for mass-producing EESMs.
EESMs as well as the larger OEM story played a role in helping land the EU-India and the UK-India FTAs because the supply chains for French+Italian (Renault, Stellantis), Japanese (Toyota, Honda, Suzuki), Korean (Hyundai-Kia), and Indian automotive manufacturers merged.
On the other hand, EESM EVs aren't a thing here in North America nor China yet as both primarily use PMSMs (edited typo).
[0] - https://news.ycombinator.com/item?id=48510402
[1] - https://leandesign.com/nissan-ariya-magnet-free-motor-teardo...
[2] - https://www.bmwblog.com/2025/02/20/bmw-gen6-electric-motors-...
[3] - https://www.reuters.com/world/china/india-revs-up-alternate-...
---
Edit: can't reply
> does Nissan still use these motors, the car in the linked article has been discontinued
Yes. The Ariya was discontinued in North America (EDIT: USA, TIL still sold in Canada) but is still manufactured and sold in Asia.
> European and Indian manufacturers/engineering are definitely not in the same category though
It's the same manufacturers and supply chain now.
Renault and their OEMs are the biggest driver for EESM, and Renault's largest markets and manufacturing hubs are France, India, and Romania. Heck, Renault is now going to start exporting it's Made in India cars and parts back to the EU [0] becuase of the EU-India FTA.
And the European OEMs have transferred the IP for EESMs to Indian JVs as I mentioned. It's the same style of tech transfer as Samsung did for BYD and TDK for CATL for battery chemistry in the 2000s. Heck, Valeo [1], MAHLE [2], ZF [3], and Schaffler [4] are opening and expanding factories and R&D hubs dedicated to EV transmission manufacturing in India for domestic and export usecases.
Also, if you've ever driven a Japanese (Toyota, Honda, Suzuki) or Korean (Hyundai, Kia) make care in the EU, Australia, Middle East, Africa, or Asia outside of their home countries their parts sourcing and even the entire manufactured car would have come from India, such as the Toyota Urban Cruiser EV [5].
[0] - https://m.economictimes.com/industry/auto/auto-news/india-eu...
[1] - https://www.valeo.com/en/valeo-inaugurates-new-electric-powe...
[2] - https://auto.economictimes.indiatimes.com/news/auto-technolo...
[3] - https://press.zf.com/press/en/releases/release_66050.html
[4] - https://www.basispointinsight.com/Story/schaeffler-india-ope...
[5] - https://newsroom.toyota.eu/the-all-new-toyota-urban-cruiser/
No, and it was mentioned by the consortium of European cars manufacturers after the joint press release with Der Leyen herself: the implementation of factories and research centers in India is solely to be able to sell on that market. It is the exact same process that happened with China in the past. The exact same also happened with Airbus.
You are also wrong on the market importance for Renault. For 2024, France was the biggest, followed by Italy, Turkey, Spain, Germany, Brazil, UK, Morocco, BENELUX, Romania, Poland, Netherlands and... #13 India with 0.9% market share...
Supply chains didn't change at all, in fact it did the opposite, and Europeans won't rely on anything Indian made for the near future, as local re-industrialization is already acted on and even accelerated since the pandemic.
Production numbers across all manufacturers even Volkswagen (which was unexpected) show the number of cars manufactured in Europe increased in the past 2 years.
Electric cars in Europe mostly come from China, the US and European brands. Nothing Indian-made, not even parts.
Not sure why this was voted down, it was the most useful comment here.
does Nissan still use these motors, the car in the linked article has been discontinued, and then only real info I can find on their site about the leaf is about their ROCKIN' bose sound system/s
Because it's grossly untrue and backed with propaganda slop articles. I suspect this is a bot.
European and Indian manufacturers/engineering are definitely not in the same category though.
> The Ariya was discontinued in North America but is still manufactured and sold in Asia.
The Nissan Ariya is NOT discontinued in North America. Nissan no longer sells it in the USA because of Trump's tariff war.
The Nissan Ariya is still sold in Canada.
what is a prsm? Do you mean pmsm?
It's a bummer they are not really available in the US.
EVs in the US and China tend to use PMSMs, though GM, Stellantis, the DoE, and the DoD are funding an EESM startup [0]
[0] - https://nironmagnetics.com/
Does regenerative braking work with a motor like this?
Yes: IIRC some large generators work exactly like this, as the energized rotor gives a lot more flexibility in managing frequency and power output.
Not just some, approximately all of them. It greatly complicates the logistics of a black start. † Of course that situation has additional complexity due to the need for substantial additional power in order for the various fuel supply systems to operate but I digress.
† https://en.wikipedia.org/wiki/Black_start
After watching a Munro video about it, I see your point. In the motor shown, the rotor gets its magnetic field simply by inducing a current and a field in it in reaction to the stator's field. There are no electromagnets in the rotor like I expected. In that case, I'm not sure either... I'd say more likely than not but it's complicated since the stator basically needs to induce a field and at the same time recover energy from the field that comes back from the rotor. I would further guess that the phase shift between the two components makes it possible to treat them separately.
Previous comment: Don't see why not - the "field" coils (the ones that replace the permanent magnets) need to be energized, which can initially come from the batteries if necessary.
There are electromagnets in the rotor, it is directly energized.
Seems to be: replace permanent Nd magnet with an electromagnet.
There is something... weird about this. this tech has existed.... a long time. And I am not familiar with what is common in electric cars so may be missing something obvious but thought this was already how it was done. let me explain my limited understanding.
With ac motors electromagnets can be used in the rotor. there is even a super clever way to do it where the electromagnet in the rotor is driven wirelessly via induction. there are some downsides but having no physical sliding electrical connection to the rotor is a huge upside. The ac can be dynamically formed from DC via high speed switching(transistors, in industry often called a VFD).
Due to the upsides of ac induction motors I sort of assumed this was already what was found in cars. I am a bit surprised to find out there were rare earth magnets in the first place.
Permanent magnet motors are simpler and cheaper to make, at least in the small (yes, small --- there are electric motors in the MW range in industrial applications, which are themselves larger than an average car) sizes found in EVs.
AC motors are not magic. The core is essentially just a coil with one turn, so it can generate only a very limited magnetic field. So they have to be bulkier for a given power density and generally slightly less efficient.
They even use regular carbon brushes to supply power to the magnet. Munro has a teardown video for a similar motor for Nissan: https://www.youtube.com/watch?v=BFmp9ODkCA8
So does it consume significantly more electricity?
Not really. The excitation power is a small fraction of the total.
The problem is that it makes the rotor far less mechanically robust and also heavier. That's why these motors are less powerful.
let me guess.. but its 2x the price?
no, but requires introduces brushes (slip-rings really) which is a wear item
I don't think car owners have to worry about this the first half million miles or so with these motors. Electrical motors last a long time. We'll know for sure in a few decades, I guess. That's how long it will take for a significant number of their cars to actually drive that far.
Also, compare this to ICE engines which experience continuous explosions, lots of mechanical parts, extreme temperature swings, etc. and still manage pretty decent durability. There's simply no base for assuming that parts like this wearing out and needing to be replaced is going to be a common thing.
The Continental and Renault motors like those in my Kangoo ZE and Zoe have so far proven fairly reliable, with the occasional exception being shaft bearings. The Q210 is particularly robust. I'm not aware of anybody having brush/slip ring issues yet.
Cars already have lots of wear items and a mature service industry for them. If I can reliably get at least 50k miles out of it, then I wouldn't be all that bothered, as this is not likely to be an expensive part or service.
> mature service industry for them
The car service industry is a scam, and I am glad that EVs require minimal to no servicing that cannot be easily DIY like tires and brakes.
so apparently on the BMW i4s it requires a rear subframe drop which isn't going to be cheap (10s of hours).
The main difference between this and your typical AC induction motors (also magnet free) is that this is a DC motor so you need a commutator. Your AC induction magnet free motors are very similar to drone motors in that you don't have any electrically active moving parts like slip rings and commutators. But for AC induction there will be a slight lag (known as slip).
They are electronically commutated. The stator field is more or less variable AC.
The inductance ones yes, not these ones.