userbinator
A historical pioneer in the complex technology of electric
motors without magnetsThose 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.
|
> xeonmc
What advantage do permanent magnets provide that it
isn't the case that all motors are made without them?
|
> > sitharus
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.
|
> > > Rapzid
To a layman that seems like a really small
efficiency tax if you can't get your hands on
the magnets for some reason.
|
> > > > handstitched
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.
|
> XorNot
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).
|
> > Jblx2
And if you also ignore iron saturation.
|
bgarbiak
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.
|
> PedroBatista
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?
|
> > lostlogin
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.
|
> > nine_k
It's still good to know that SOTA is further, and
we can expect the more advanced designs to seep
into more affordable segments.
|
> > fnord77
same order of magnitude :)
|
> > alephnerd
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-as
ks-eu-enco...[1] -
https://www.globaltimes.cn/page/202605/1361926.sht
ml[2] -
https://www.chinausfocus.com/finance-economy/dear-
brussels-d...[3] -
https://www.globaltimes.cn/page/202605/1362161.sht
ml[4] -
http://news.china.com.cn/2026-06/10/content_118541
873.shtml[5] -
https://fddi.fudan.edu.cn/_t2515/57/f8/c21257a7434
16/page.ht...[6] -
https://www.reuters.com/business/aerospace-defense
/russians-...[7] -
https://www.pravda.com.ua/eng/news/2026/06/12/8039
041/
|
> Quarrel
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.
|
> > andwur
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.
|
giobox
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.
|
> hnav
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).
|
> > genter
I've probably taken apart 10 automotive
alternators. Every single one had brushes.
|
> > > hnav
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).
|
> > dheera
Slip rings have brushes.
|
> > > raverbashing
Yes but they wear less than DC brushed motors
exactly because it's a slip ring and not a
commutator
|
> > > > ahartmetz
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.
|
willXare
"Replace the magnet with a controllable magnet" is
probably the most automotive-engineering sentence
possible.
|
> pfannl
Also known as: "we removed the rare earths and added
software."
|
> > Jblx2
Synchronous motors: running on software since the
1880s. Nikola really was ahead of his time!
|
> > > hnav
He invented the induction motor which runs
right off the grid.
|
numpad0
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.
|
delfugal
How soon to see rare-earth-free paired with CATL Sodium
batteries? Seems a price war, range war is imminent.
|
> cogman10
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.
|
> > Manuel_D
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.
|
> > MaKey
One of the most interesting features of sodium
batteries is that they still perform good in cold
temperatures.
|
> > > cromka
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.
|
> > gpm
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.
|
> > nine_k
Looks ideal for a power wall at home.
|
> > AtlasBarfed
Superior temperature range in cold weather as well
IIRC.
|
> alephnerd
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/solidelectroly
tefaci...[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-062
f7620f...[6] -
https://www.reuters.com/world/china/eu-lawmakers-rebuk
e-chin...[7] -
https://blog.lgchem.com/en/2026/03/25_solid_state_batt
ery/
|
ipbrown
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.
|
MrDrMcCoy
It's a bummer they are not really available in the US.
|
> alephnerd
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/
|
alephnerd
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-tear
do...[2] -
https://www.bmwblog.com/2025/02/20/bmw-gen6-electric-motor
s-...[3] -
https://www.reuters.com/world/china/india-revs-up-alternat
e-...---Edit: can't reply> does Nissan still use these
motors, the car in the linked article has been
discontinuedYes. 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 thoughIt'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-po
we...[2] -
https://auto.economictimes.indiatimes.com/news/auto-techno
lo...[3] -
https://press.zf.com/press/en/releases/release_66050.html[
4] -
https://www.basispointinsight.com/Story/schaeffler-india-o
pe...[5] -
https://newsroom.toyota.eu/the-all-new-toyota-urban-cruise
r/
|
> IlikeMadison
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.
|
> analogpixel
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
|
> > IlikeMadison
Because it's grossly untrue and backed with
propaganda slop articles. I suspect this is a bot.
|
> heresie-dabord
> 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.
|
> IlikeMadison
European and Indian manufacturers/engineering are
definitely not in the same category though.
|
> AtlasBarfed
what is a prsm? Do you mean pmsm?
|
isopede
Does regenerative braking work with a motor like this?
|
> cwillu
Yes: IIRC some large generators work exactly like
this, as the energized rotor gives a lot more
flexibility in managing frequency and power output.
|
> > fc417fc802
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
|
> ahartmetz
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.
|
> > maxerickson
There are electromagnets in the rotor, it is
directly energized.
|
derac
https://youtu.be/FHufjrP0xDI?is=xmFQrXGa1dBHM67IThis is a
helpful explanation of what this technology is and looks
like. (Munro)
|
> lowbloodsugar
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.
|
dmitrygr
Seems to be: replace permanent Nd magnet with an
electromagnet.
|
> somat
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.
|
> > userbinator
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.
|
> > cyberax
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.
|
> cyberax
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
|
> dyauspitr
So does it consume significantly more electricity?
|
> > cyberax
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.
|
hijinks
let me guess.. but its 2x the price?
|
> hnav
no, but requires introduces brushes (slip-rings
really) which is a wear item
|
> > themafia
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.
|
> > > drnick1
> mature service industry for themThe 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.
|
> > > hnav
so apparently on the BMW i4s it requires a
rear subframe drop which isn't going to be
cheap (10s of hours).
|
Onavo
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).
|
> maxerickson
They are electronically commutated. The stator field
is more or less variable AC.
|