Renault frames the EESM as a way to eliminate dependence on neodymium and dysprosium — materials whose supply chain is dominated by China and now subject to tightened October 2025 export controls. The company emphasizes that the Megane E-Tech, Scenic E-Tech, and new R5 ship with zero rare earths in the rotor, positioning supply-chain sovereignty as the primary win.
Argues the design itself is century-old electrical engineering — wound-rotor synchronous machines have powered TGVs since the 1980s and the original Zoe in 2012. What changed in 2026 isn't the physics but the geopolitics: China's 0.1% rare-earth threshold rule makes even 'non-Chinese' magnets touched by Chinese refineries export-controlled, forcing automakers to revive an older architecture.
Renault openly acknowledges the architecture introduces moving electrical contacts (carbon brushes and slip rings that wear), an extra control variable in the rotor excitation current, and a small efficiency penalty at partial load. They claim 96% peak efficiency at 200 kW — within roughly two points of an equivalent PMSM — framing the gap as acceptable given the supply-chain benefits.
Frames the EESM honestly as a trade-off: you swap permanent magnets for wound copper, gaining rare-earth independence but accepting brush wear, extra control complexity, and a ~2-point efficiency penalty versus PMSMs that dominate Tesla, BYD, and Hyundai. Notes BMW (iX, i4) and Nissan (Ariya) have already validated the architecture is production-viable.
Renault Group published a technical explainer this week — picked up by Hacker News to 379 points — on the electrically-excited synchronous motor (EESM) it now ships in the Megane E-Tech, Scenic E-Tech, and the new R5. The pitch is simple: zero rare earths in the rotor, zero neodymium, zero dysprosium, and zero exposure to a Chinese export-control regime that tightened again in October 2025.
The design itself is not new. Wound-rotor synchronous machines have powered French TGVs since the 1980s and showed up in the first-generation Renault Zoe back in 2012. What's new is the manufacturing maturity: Renault and Valeo's joint motor, built in Cléon, hits 200 kW at a claimed 96% peak efficiency — within roughly two points of an equivalent permanent-magnet synchronous motor (PMSM), the architecture that dominates Tesla, BYD, Hyundai, and essentially every other production EV.
The mechanism: instead of embedding permanent magnets in the rotor, Renault winds copper around it and runs current through carbon brushes and slip rings to create the magnetic field on demand. No magnet, no rare earth. The trade-off is exactly what you'd expect — moving electrical contacts (brushes wear), an extra control variable (rotor excitation current), and a small efficiency penalty at partial load. BMW ships the same architecture in the iX and i4. So does the Nissan Ariya. The HN thread's most-upvoted technical comment summarized it bluntly: "This is 1890s electrical engineering, productionized in 2026 because the geopolitics changed."
The rare-earth supply chain is not a market — it's a chokepoint. China refines roughly 90% of the world's neodymium and over 99% of the heavy rare earths (dysprosium, terbium) that magnets need to survive a hot motor. In October 2025, Beijing extended its export-license regime to cover magnets containing as little as 0.1% Chinese-origin rare earths — meaning even "non-Chinese" magnets touched by a Chinese refinery now require an export license. The license takes 45 days minimum. Several European Tier-1 suppliers reported June-quarter production pauses.
What Renault is demonstrating is that the workaround was sitting in textbooks the whole time. The cost is roughly 2-3 percentage points of efficiency, 5-8% more copper, and a brush service interval somewhere around 300,000 km. For a passenger car, that is not a catastrophe. For a fleet operator running million-kilometer commercial duty cycles, it might be. The point is that the trade is now legible, not hypothetical.
The HN comment pattern is worth reading. The top thread is not the usual EV-vs-EV flame war — it's mechanical engineers and power-electronics people explaining, calmly, why this architecture was abandoned in the first place (magnets got cheap, dysprosium got abundant, control electronics for rotor excitation were expensive in the 90s) and why each of those conditions has now reversed. SiC inverters made the control problem trivial. Magnet prices spiked 4x between 2020 and 2024. Dysprosium is now a national-security line item in three different countries' industrial policy documents.
The contrast with how the U.S. and Tesla are responding is sharper than the press releases admit. Tesla's announcement that the next-gen drive unit would use "a permanent magnet motor with no rare earths" — made at Investor Day 2023 — has produced no shipping vehicle as of mid-2026. The credible read is that they're chasing ferrite-magnet PMSMs, which work but cap out at lower torque density. Renault took the other fork: keep the torque density, accept the brushes, ship now.
If you build hardware, this is the template. The 2026 cost of avoiding a geopolitical chokepoint is no longer measured in dollars — it's measured in engineering complexity you have to choose to absorb. Your BOM has a Chinese-controlled component. You can (a) pay the export-license tax and the 45-day lead time, (b) substitute an inferior material and eat the spec hit, or (c) redesign around a different physical principle and eat the engineering hit. Renault picked (c). Most of your competitors are still hoping (a) holds.
The pattern generalizes beyond motors. Gallium for RF power amplifiers. Germanium for fiber optics and IR sensors. Tungsten for, well, everything that needs to be hard and heat-resistant. Each one is sitting at >80% Chinese refining share. Each one has a textbook substitute that was abandoned when the dominant material got cheap. The engineering work to bring those substitutes back to production is real, but it's bounded — it's not a research problem, it's a manufacturing-process and tolerance-stack problem.
For software people watching from the sidelines: the analog is real. You depend on a registry, a CDN, a base image, an API. The cost of multi-sourcing looks pure overhead until the day the chokepoint closes. The discipline of asking "what's our wound-rotor fallback for this?" — and actually building the prototype before you need it — is the same muscle whether the dependency is dysprosium or a particular hosted vector database. The comfortable answer is that the chokepoint will hold. Renault is hedging that it won't.
Expect VW, Stellantis, and at least one Korean OEM to announce EESM programs within twelve months — most of the IP is generic and the supplier base (Valeo, ZF, Bosch) is already tooled. The interesting question is whether the U.S. industrial base catches up: GM and Ford have no announced rare-earth-free production program, and the IRA's domestic-content rules incentivize sourcing, not redesign. If the next round of Chinese export tightening lands in 2027 as several analysts expect, the OEMs without a wound-rotor option in the pipeline will be the ones explaining to investors why their margins just compressed.
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.
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.
Clearly making a motor with induced magnetic fields both for the stator and rotor isn't the innovation here, since a large fraction of industrial motors do not have permanent magnets.I would assume the innovation here would need to be making it small and efficient for any meaningful torque outp
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.
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Unfortunately, their Web page does not say a single word about the important problems of their motors.The electrically excited synchronous motors have been known forever, but they had not been used in EVs because of 2 disadvantages.The first is that traditional EESMs require brushes, i.e. sliding el