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.
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.
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]
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.
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.
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.
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.
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.
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.
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.
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].
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
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.
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).
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.
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.
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.
It's still good to know that SOTA is further, and we can expect the more advanced designs to seep into more affordable segments.
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]
[0] - https://www.reuters.com/world/china/renault-ceo-asks-eu-enco...
"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.
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.
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.
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/
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.
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.
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.
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.
let me guess.. but its 2x the price?
no, but requires introduces brushes (slip-rings really) which is a wear item
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.
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/
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?
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.
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.
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.