Electric motors with no rare earths

> such motors require frequent maintenance for changing the brushes.

"Frequent" is all relative.

The Renault Zoe, 10y ago, was already using a synchronous engine with wired rotor. And most were going over 150kkm without any issues nor brush changes.

> because the electrical currents that circulate through the rotor windings must generate heat

Currently stator heat in wired synchronous engine is less a problem than in SynRMs with permanent magnets.

Most neodymium based permanent magnets start to be irreversibly damaged id they heat up beyond 100°C. That's currently why Tesla has such a good cooling system in their engine.

Wired rotor are bunch of copper coil, as such they are much more resistant to temperature gradients.

Munro took apart a Nissan Ariya which has this exact kind of motor. The maintenance is basically removing a tiny cover and replacing the tiny and cheap carbon brushes every 100k km or more. It's basically cabin filter level maintenance.

And they said that PMSM motors are more efficient at low RPM, but their coils get saturated at higher RPMs meaning they lose efficiency at highway speeds (which actually affect the range number people car about).

So overall not such a bad tradeoff, if it makes cars less expensive.

Interesting question, it looks like they are / will be brushelss:

> Group will gradually embed new technological improvements from 2024 on its EESM: stator hairpin, glued motor stack, *brushless* and hollow rotor shafts.

[0] https://www.evspecifications.com/en/news/6ec9484

That said, what sibling says about the maintenance problems is very true. :-/

> The second disadvantage is a lower efficiency than with permanent magnets, which cannot be improved so much as to match PM motors, because the electrical currents that circulate through the rotor windings must generate heat. The lower efficiency also makes cooling more difficult.

It depends.

With PM motors if you exceed the Curie temperature, the magnets lose their magnetism. Also one can control the rotor excitation current on EESMs so core saturation is less of an issue compared to PMSMs.

The brushes are also quite long lasting and easy to change on a good design so maintenance is not as a big of an issue.

ASMs are even more robust but they have lower power density and efficiency but are better for coasting.

There is also the SynRM which uses an unwound rotor with flux barriers (cutouts) that aligns with the stator flux, no magnets needed. It's basically as robust as the ASM but without its lower efficiency disadvantages and also no brushes, at the cost of more complex power electronics and lower speed noise.

TFA does specifically call out the lower efficiency of eesm. I guess it was edited after you wrote your comment.

Efficiency schmischiency. I see your 3% and raise you the abolition of SUVs.

I see your motor-brush maintenance burden with my washer fluid, tyres, brakes, seals bearings bulbs filters etc etc. Then I raise you control modules that send your car to three garages and the scrapyard. Cars have wear items, you heard it here first.

Efficiency varies according to the load and RPM.

Permanent magnet motors have higher peak efficiency but EESMs are better in non ideal conditions, particularly low torque high RPM i.e. highway cruising where efficiency is more critical than at low speeds.

> so such motors require frequent maintenance for changing the brushes.

Define frequent. I maintain machinery with brushes so I have a decent idea of what life span should be depending on the environment. If the housing for the slip ring setup is well protected from dirt and the slip rings aren't cleaned by a cave man you can get a few years of life from the brushes.

Not sure how familiar you are with Renault, but “maintenance problems” pretty much sums up a lot of older Renaults.

> The second disadvantage is a lower efficiency than with permanent magnets, which cannot be improved so much as to match PM motors, because the electrical currents that circulate through the rotor windings must generate heat. The lower efficiency also makes cooling more difficult.

Wouldn't the back EMF help here? In brushed DC motor it surely does, reducing losses way below what full voltage over winding resistance would incur.

> electrically excited synchronous motors

So hold on, their amazing technological innovation is... <drum roll please>

a washing machine motor?

Amazing breakdown for someone (me) who knows literally nothing about how motors work.

>Losing a few percents in efficiency is an acceptable compromise for avoiding the use of expensive and supply-constrained chemical elements.

Is it? A 1% decrease in efficiency means increased fuel costs for the user. Acceptability should be based on the long term costs v short term savings to the customer.

It's this myopic, Thinking from the pov of the company, that leads to enshittification. I don't think we should be unquestionly accept that pov.

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.

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.

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).

What advantage do permanent magnets provide that it isn't the case that all motors are made without them?

Verbiage? What about the _nounage_?

[flagged]

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?

    > BMWs have a terrible record for needing expensive repairs.

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.

I don't know. Europe had the opportunity to make themselves energy independent multiple times; instead they doubled down on Russian oil, and in response to the latest invasion, they instead doubled down on Qatar natural gas...

Germany spent enough on solar to have nuclear power for winter heating and instead they get nearly nothing from it when energy (note I said Energy not Electricity) demand is the highest: winter heating.

Now, if they had put that solar in North Africa and ran cables, sure, but they didn't. Or if they did Drake's landing solar storage, that would also work. But they spent a fortune only to still be completely dependent on fossil fuels and are destroying the economic base because of the cost.

In the long term solutions will be found, but in the short term they can gain an enormous bargaining chip. If food prices double because we've burnt the last drop from the Strategic Petroleum Reserve, the administration will give them just about anything they want to avoid utter political destruction.

The game theoretic definition of a threat is something that harms you, but harms them so much that they will avoid forcing you to trigger the threat. It's a different matrix from the Prisoner's Dilemma, but still leaves you guessing about the personality of your opponent. The personality of Iran seems reasonably consistent. The US, less so.

"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.

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).

It's brushless: https://www.evspecifications.com/images/news/6ec9484/additio...

The real innovation is in making them brushless and essentially maintenance free while still being efficient enough.

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.

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/

I see another advantage..

You can switch a motor without permanent magnets to "idle mode".

I understand in Tesla dual motor configurations, the front motor is without magnets. The excitation field will be turned on when you need extra power, but at crusing speed it does not cause extra "drag". From one teardown I've seen, they even went so far to use cheaper and less efficient IGBTs for the front drive, and more efficient SiC Mosfets for the rear motor (in the same vehicle!). If you need extra acceleration briefly, lower efficiency can be accepted.

It’s interesting that EESMs can be more efficient at high/highway speeds, and it’s something I had read before. This seems to me to be a key advantage of EESMs, because when people worry about EV range, they worry mainly about range on long-distance, high-speed journeys.

(I have a Renault EV and it’s excellent. Aside from the motor technology, it’s relatively light, has a heat pump as standard, and a good-sized battery).

As said in the parent Web page, lower energy efficiency, thus shorter range with the same battery.

Another poster has mentioned that BMW also uses EESMs instead of permanent-motor magnets.

BMW uses EESMs as the main motors, on the rear axle, while they use induction motors as auxiliary motors on the front axle.

Besides being cheaper, the induction motors have the advantage that if they are used only as auxiliary motors, you can cut the power supply to them at any time, in which case they will consume nothing.

So their lower efficiency does not matter, because most of the time they are turned off.

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.

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.

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?

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

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?

They are electronically commutated. The stator field is more or less variable AC.

I iiiioiooo iko to keep up ok it iiiioiooo the same i

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/

Yes: IIRC some large generators work exactly like this, as the energized rotor gives a lot more flexibility in managing frequency and power output.

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.

Practically speaking, yes: I have a Renault EV and the battery % goes up on long descents.

I also have a Zoé (an R135). Wonderful little machine.

no, but requires introduces brushes (slip-rings really) which is a wear item

Also known as: “we removed the rare earths and added software.”