Litz Wire in Electric Motors: EV Traction Motors, High-Speed PMSM, Aviation, Steppers and BLDC
October 2025 brought two pieces of news about the future of motor engineering at once. Fraunhofer, under the European Project AMBER, unveiled an electric aircraft with a motor delivering 1,000 horsepower at a mass of 94 kg, running at speeds up to 21,000 rpm. Hofer and Pankl simultaneously announced an integrated electric turbocharger built on Form Litz winding technology — profiled litz wire. Two independent announcements from Germany and Austria, two industrial products with a two-to-three-year time horizon. Both with litz-wire windings.
This is a telling snapshot of what has happened to litz wire in motors over the past three years. What in 2015 was a solution for narrow, specialized machines had, by 2025, become the mainstream of engineering development. The reason is physical: inverter switching frequencies have risen from a few kilohertz (IGBT) to forty (SiC and GaN), rotor speeds have reached 100,000-200,000 rpm in turbomachinery, and the weight-and-size requirements of electric transport and electric aviation have turned the fight for every percentage point of efficiency into the central engineering task. Under these conditions, litz wire in the winding is not an option but the only way to pack copper so that the winding works as a winding rather than as a heater.
This article covers five classes of motor where litz wire delivers a measurable gain, with concrete figures from IEEE and MDPI papers of 2023-2025, a description of the manufacturing details, and a note on where our products fit in.
1. Why motors turned to litz wire
An electric motor running at the 50 Hz utility frequency does not need litz wire. The skin effect in a 0.5 mm copper strand at that frequency is negligible — the skin depth is 9.3 mm and the strand is electrically uniform. Round enamelled wire, a hairpin bar, CTC — everything works. So why litz?
A modern motor does not run at 50 Hz. Three trends of the 2020s have pushed winding losses to the forefront:
Rising inverter frequency. SiC and GaN inverters switch at 20-40 kHz with edges shorter than 100 nanoseconds (Ji et al., IEEE TAES 2023). The winding-current spectrum is not a clean sinusoid at the utility frequency but the sum of a fundamental plus strong harmonics reaching tens of kilohertz. At 20 kHz the skin depth in copper is 0.47 mm. From that standpoint a round 2 mm strand is electrically four times too thick: the current flows in its outer ring, the center does no work, and the AC resistance rises.
Rising rotor speed. Traction motors on 800-volt platforms run up to 20,000 rpm, electric turbochargers up to 100,000, and in some turbo-electric-propulsion work up to 200,000 rpm (Zhang, IET 2018, 200 kRPM HSP PMSM). For a ten-pole motor at 200,000 rpm the fundamental electrical frequency is 16.7 kHz. That is already a normal operating frequency for litz wire, not a special case.
Current and packing density. A 1,500 kg electric vehicle needs a traction motor with a mass of 50 kg and a power of 150 kW. A regional-class electric aircraft needs a 500 kW motor at a mass of 70 kg. Such figures are only achievable at a copper packing density of 0.75-0.85 — and in that packing, round enamelled wire with gaps at the corners loses catastrophically to tightly packed litz wire.
The three trends — rising frequency, rising speed, rising density — are independent, yet all three point to one and the same engineering answer. Hence the wave of IEEE and MDPI papers in 2023-2025 on litz wire in motors.
All three conductors have the same copper cross-section, ~5 mm². At the 50 Hz utility frequency there is no difference — they all behave identically. At 10 kHz (the fundamental electrical frequency of an 8-pole EV traction motor at 15,000 rpm), 92% of the loss in the solid wire is parasitic eddy currents; for hairpin it is 74%; for litz wire, 13%. At 40 kHz (a normal SiC inverter switching frequency) the solid wire heats 45 times more than at DC, hairpin 5.5 times, litz 1.35. Figures after Born et al. (EDPC 2022) and Shevyreva et al. (MDPI Electronics 2025).
2. EV traction motors: hybrid hairpin + litz
2.1 The problem with pure hairpin
Since 2015 the hairpin winding — a U-shaped rectangular conductor inserted into the stator slot and laser-welded at the crown — has become the standard for traction motors. It is used by virtually every major manufacturer: Tesla Model S Plaid (a tri-motor system with a combined peak power of 760 kW), BMW iX M60 (455 kW on an 800-volt platform), Porsche Taycan Turbo S (560 kW), Mercedes EQS 580 (385 kW), VW ID.4 (the 150 kW APP310 unit), and Hyundai Ioniq 5 on the E-GMP platform. A slot fill factor of 0.7-0.8, automated assembly with laser welding at the crown, mechanical strength, and resistance to centrifugal loads — these are all strengths of hairpin.
And it has the same weak spot: at high frequencies the copper loss rises quadratically. For a motor with an eight-pole rotor and a maximum speed of 18,000 rpm the fundamental electrical frequency is 1.2 kHz, but the SiC inverter switches at 15-20 kHz, and that entire frequency band reaches the winding as a noise spectrum of current. Shevyreva et al. measured, on a real 150 kW IPMSM for EV, that the RAC / RDC ratio of hairpin at inverter frequencies reaches 3.5-5 (MDPI Electronics, vol. 14, no. 17, 3350, 2025). Half, and sometimes the larger part, of the winding's heat generation comes not from the useful DC current but from parasitic eddy currents inside the solid rectangular conductor. Specifically: at a typical 90 km/h cruise with a 150 kW motor, the useful phase current is 85 A, the DC loss is 35 W per winding, and the AC contribution at RAC/RDC = 4 is another 105 W. That is, three quarters of the winding's heat generation is parasitic eddy currents that have to be eliminated somehow.
2.2 The hybrid architecture
From 2023-2024 a new design took hold in the industrial literature: hairpin in the slot plus litz wire in the end windings. The logic is simple. Inside the slot the magnetic field is comparatively uniform — the main proximity-effect losses arise where the field changes sharply, that is, in the end windings. Hairpin works in the slot but not in the end windings. So the slot stays on hairpin (preserving density and automation) while the end windings switch to continuously transposed litz wire.
The paper "Design Analysis of an Interior Permanent Magnet Synchronous Motor with Hybrid Hair-Pin and Litz Wire Windings" (Shevyreva et al., MDPI Electronics, 2025) presents a direct simulation over the leading WLTP Class 3 cycle: a hybrid IPMSM versus pure hairpin. The headline result is an average efficiency gain of 1.5-2 percentage points, and this is not a peak improvement but the average over the entire drive profile. At specific operating points — 50 N·m at 15,000 rpm and 90 N·m at 8,000 rpm — the gain reaches a 10-15% reduction in total losses.
Longitudinal section of the stator along the motor axis. The gray bars top and bottom are the iron stack (laminated stator iron); between them run two conducting paths (the upper and lower layers of the hairpin winding). To the left and right of the stack are the end windings, where the conductors exit and turn over to the neighboring slot. The red gradient = solid hairpin bar, with a bright core showing the concentration of eddy currents. The green dots = transposed litz wire, each dot a separate thin strand. In Hybrid mode the slot stays on hairpin (the field inside the iron is uniform — eddies are harmless), while the end windings are converted to litz (where the field "diverges," and the proximity effect accounts for most of the AC loss right there). Data on the right: 150 kW IPMSM, 20 kHz SiC inverter, 200 A RMS.
2.3 A parallel track: Formed Litz Wire
Another direction, developed at RWTH Aachen and Schaeffler, is Formed Litz Wire Stator Windings (Born et al., EDPC 2022; Wulfinghoff et al., ResearchGate ID 366408980). The idea: take high-frequency litz wire, profile it into a rectangular cross-section, and then insert it into the stator slot in the form of a rectangular bar instead of ordinary hairpin. The result is a structure externally identical to a hairpin motor but internally transposed, with the proximity effect suppressed.
A concrete calculation from Born et al.: a 150 kW IPMSM, 8 poles, 48 slots, maximum speed 18,000 rpm. Round enamelled wire with five parallel 2.2 mm strands in hairpin format gives RAC/RDC = 3.8 at 10 kHz and 5.5 at 20 kHz. Formed Litz of 450 strands of 0.1 mm, profiled into a 3.5×2.8 mm rectangle, gives RAC/RDC = 1.15 and 1.30 respectively. At an average phase current of 200 A that is a copper-loss difference of 180 W versus 30 W per winding — that is, litz wire removes 150 W from each of the motor's six windings, or 900 W in total.
In October 2024 Schaeffler announced the start of series production of stators using its Continuous Wave Winding (CWW) technology — automated stator assembly from a single, continuously wound litz-wire "web," formed into a rectangle and laid into the slots as one piece. This is a direct industrial outcome of the 2022-2023 RWTH Aachen work.
Formed litz wire is exactly the product that we at Diada produce in a single pass together with the insulation (more in the article on rectangular litz wire). For traction motors a rectangular litz cross-section is not exotic but a working format. A typical grade for this task is LitzPr 200 PI (class 200, polyimide jacket for PDIV resistance under SiC inverter supply, rectangular cross-section matched to the geometry of the specific slot).
2.4 Figures and economics
A 150 kW traction motor, at an average annual EV mileage of 15,000 km, consumes about 2,500 kWh of energy per year. An efficiency gain of 1.5 percentage points is 37.5 kWh saved per year per car. Across a fleet of 100,000 EVs that is 3.75 GWh, equivalent to a continuous power of 430 kW. In the tariffs of the Russian market in 2026 (the wholesale electricity market) that is millions of rubles. But the main thing is the gain in driving range without increasing battery mass, which in the EV segment is deciding the competitiveness of specific models right now.
3. High-speed PMSM: e-turbo, e-compressor, turbomachinery
In marketing materials, electric turbochargers and fuel-cell compressors are often called "brushless motors" or "BLDC," but formally these are permanent-magnet synchronous motors (PMSM) under vector (FOC) control. We address the difference between PMSM and BLDC as classes separately in section 5 — there it bears directly on the choice. This section covers applications where the motor is always a PMSM with a distributed winding: high speed, sinusoidal field, litz wire in the winding.
3.1 Electric turbochargers (e-turbo)
An electric turbocharger is the turbocharger of an internal-combustion engine in which the turbine wheel is spun not by exhaust gases but by an electric motor. Applications include hybrid cars, diesel power plants, and electrically assisted marine engines. The characteristic rotational speed is 100,000-150,000 rpm and the power 3-15 kW.
Specific products on the market:
- BorgWarner 48V eBooster — fitted to the Audi SQ7, Bentley Bentayga, Mercedes-Benz S-Class. A 7 kW motor, speed up to 70,000 rpm, 48 V.
- Garrett Motion E-Turbo — fitted in series to the Mercedes-AMG C 53 and E 53 (hybrids), and to Formula 1 cars (ERS-K). The electrical part is 4 kW, speed up to 120,000 rpm.
- Mitsubishi Electric FCEV air compressor — for the fuel cells of the second-generation Toyota Mirai and the Hyundai NEXO. 25 kW, 100,000 rpm, direct winding with litz wire.
- MAHLE Powertrain e-compressor — a universal platform for BEV cabin air conditioning and FCEV air supply, 8-30 kW.
Lee et al. (MDPI Electronics, vol. 12, no. 13, 2937, 2023) describe an electric-turbocharger motor: 3 kW, 100,000 rpm, SPMSM, 6 poles. The electrical frequency at that speed is 5,000 Hz; the skin depth at that frequency is 0.93 mm, and round strands larger than 0.5 mm already become electrically thick. The design uses litz wire with thin strands (0.2 mm, 200 parallel strands) — otherwise the copper loss at the rated operating point exceeds the DC copper loss by a factor of 4, the winding overheats, the Nd-Fe-B magnets in the rotor lose their properties, and the motor fails within minutes of operation.
A typical litz-wire grade for such tasks is Litz 200 PI 200×0.2 or Litz PET 400×0.15 depending on the target winding temperature. A 0.1-0.2 mm strand series with a polyimide jacket for operation in the hot under-hood environment.
3.2 Integrated hofer/Pankl systems (2025)
In October 2025 hofer (Germany; electronics and motors) and Pankl (Austria; turbomachinery) announced an integrated e-turbo system built on Form Litz winding technology — profiled litz wire. The motor, inverter, turbomachinery, and controllers are designed as a single system. The goals are reduced mass, faster gas-dynamic response, higher efficiency, and a margin against vibration (NVH). Concrete numbers had not been disclosed at the time of publication, but the very fact that leading European turbomachinery developers are building a product on litz wire from scratch is a sign of the application's maturity.
3.3 Industrial turbomachines and generators
At the other end of the scale are large steam and gas turbogenerators in wind power. Here litz wire with thin strands is used together with Roebel bars in the stator windings of megawatt-class machines. The paper "Design and technology solutions for high-efficiency high-speed motors" (ResearchGate 261460810) describes real designs of 20 kW wind-power generators with litz-wire windings and epoxy vacuum pressure impregnation.
3.4 Airgap winding — a toothless design
A separate niche is high-speed PMSM with airgap windings. In such motors the iron stator teeth are absent altogether; the winding sits directly in the air gap between the stator yoke and the rotor. This produces two powerful effects: the losses in the iron teeth are eliminated (they generate a significant share of the loss at high speeds) and space opens up for a larger copper cross-section.
There is just one catch: in the air gap the magnetic field is huge and fast-changing (1 T at 15,000 Hz is typical for a 200 kRPM machine). For a round strand that means catastrophic eddy losses. An airgap winding is physically possible only with litz wire — neither hairpin, nor CTC, nor enamelled wire works under those conditions. A reference to 200 kRPM HSP PMSM prototypes with airgap litz windings is in the review by Zhang et al. (IET Electric Power Applications, 2018).
4. Aircraft motors: electric aviation and propulsion systems
4.1 The More Electric Aircraft (MEA)
The MEA concept replaces the hydraulic, pneumatic, and mechanical drives on board an aircraft with electric ones. The A380 has three autonomous AC buses for the wing actuators; the Boeing 787 has electric braking, air conditioning, and pumps. The power of the auxiliary electric motors ranges from hundreds of watts (valves) to tens of kilowatts (cabin compressors, pumps). Most of these motors run on PMSM with litz-wire windings, because aerospace requirements are simultaneously strict on weight, on efficiency (fuel burn), and on reliability over the range from −55 °C to +85 °C.
The review by Cao et al. in IEEE Trans. Ind. Electron. (vol. 59, no. 9, pp. 3523-3531, 2012) is a classic survey of motor selection for MEA. The field has developed rapidly since then, but the basic thesis is unchanged: for high-speed, high-power, inverter-fed motors litz wire is the primary winding choice.
4.2 1 MW-class electric propulsion
Since the 2020s the world has been actively developing regional-class electric and hybrid aircraft — range up to 1,500 km, capacity 20-80 passengers, pure electric propulsion. The main engineering challenge is a motor with a specific power above 10 kW/kg and an efficiency above 96%, running from a 400 V or 800 V inverter.
The paper "Optimization and Comparison of 1 MW-Class PM Motors for Aircraft Propulsion Using Litz Wire and Hairpin Windings" (IEEE Xplore, 2024, document 10908992) is a direct comparison. The authors take two variants of a 1 MW motor with 72 slots and 12 poles and a five-stage Halbach array and compute both windings — litz and hairpin — with a full FEA model. The main conclusion: hairpin gives a higher specific power by reducing the mass of active materials, but loses on AC losses; to reach the target efficiency it requires either additional genetic-algorithm slot optimization or a return to litz wire.
The general trend: every motor above 200 kW for electric aviation is today designed around a litz-wire winding by default. Hairpin remains only where the engineering team is willing to sacrifice percentage points of efficiency for specific density — in a number of prototypes that choice is made.
4.3 The cryogenic coaxial motors of the future
The most advanced direction is coaxial motors with cryogenic cooling, working together with superconducting rotor windings and a liquid-hydrogen cooling system. Such motors have already been prototyped (Ionel et al., Cryogenic Thermal System for Coreless Axial Flux PM Machine with Litz Wire Winding for Electric Aircraft Propulsion) and can deliver a specific power above 20 kW/kg at an efficiency above 99%. Here litz wire is the only winding material capable of operating across the working range from −269 °C (liquid helium) to +200 °C in the end windings — exactly the range that DuPont specifies for the Kapton films in our polyimide jacket.
Schaeffler CWW Stator
Details- Class
- IPMSM 150 kW
- Speed
- up to 18,000 rpm
- RAC/RDC
- 1.15 @ 10 kHz
LitzPr 200 PI 450×0.1Tesla Model S Plaid
Details- Power
- 760 kW peak
- Platform
- 400 V
- Winding
- Pure hairpin
BMW iX M60
Details- Power
- 455 kW
- Platform
- 800 V SiC
- Winding
- Hairpin, moving to hybrid
BorgWarner 48V eBooster
Details- Power
- 7 kW
- Speed
- up to 70,000 rpm
- Voltage
- 48 V
Litz 200 PI 200×0.2Garrett E-Turbo
Details- Power
- 4 kW
- Speed
- up to 120,000 rpm
- Class
- SPMSM 6 poles
Mitsubishi Electric FCEV
Details- Power
- 25 kW
- Speed
- 100,000 rpm
- Function
- Air supply to the fuel cell
Litz PET 400×0.15hofer/Pankl 2025
Details- Announced
- October 2025
- Integration
- Motor + inverter + turbomachinery
- Winding
- Form Litz from scratch
Rolls-Royce ACCEL
Details- Motor
- YASA, 400 kW
- Record
- 555 km/h (November 2021)
- Cooling
- Nitrogen
Fraunhofer AMBER
Details- Power
- 1,000 hp (736 kW)
- Mass
- 94 kg (7.8 kW/kg)
- Speed
- 21,000 rpm
magniX magni650
Details- Power
- 560 kW
- Application
- Electric conversion of the Cessna 208 Caravan
- Certification
- FAA 2026
Wright Electric WP-1
Details- Power
- 2 MW
- Market
- Short flights ≤1,000 km
- Platform
- BAe 146 retrofit
Siemens SP260D
Details- Power
- 260 kW
- Specific power
- 5.2 kW/kg
- Application
- Aerobatic aircraft
Abbott HeartMate 3
Details- Type
- Centrifugal motor
- Speed
- 5,400 rpm
- Condition
- Inside the patient's body
Litz PI 100×0.1 — minimal heat generationAbiomed Impella CP
Details- Speed
- 40,000 rpm
- Insertion
- Through the femoral artery
- Winding
- Litz PI thin strands
Baxter AK-98
Details- Type
- BLDC pump
- Duty
- Continuous, 4-5 h/session
- Medium
- Dialysis solutions
Litz F (PTFE for aggressive media)MRI gradient coils
Details- Frequency
- 20 - 300 MHz
- Type
- Rectangular litz
- Q factor
- Maximum
T-Motor MN505-S
Details- Diameter
- 60 mm
- KV
- 340
- Payload
- 15-30 kg
DJI Matrice 300 RTK
Details- Class
- Survey / mapping
- Motor efficiency
- 94% @ rated
- Application
- Professional aerial survey
Lin Engineering SP57
Details- Frame size
- NEMA 23
- Torque
- 2 N·m holding
- Application
- Precision drives
Click a card to flip it and reveal the specification and the typical grade marking per our TU. The filter at the top sorts by application class. The selection is not exhaustive: it is ≈20 landmark products across all five classes where the litz-wire winding is either already in series production or has been announced by leading manufacturers in 2023-2025.
5. Stepper motors and BLDC: where litz wire delivers a gain
5.0 Terminology: BLDC vs PMSM
BLDC and PMSM are two distinct classes of three-phase brushless permanent-magnet motors, differing in back-EMF waveform and control algorithm. A BLDC (Brushless DC) motor has a trapezoidal EMF, a concentrated winding, and is controlled by six-step block commutation from a simple ESC using Hall sensors — typical applications are drones, household appliances, and simple servo drives. A PMSM (Permanent Magnet Synchronous Motor) has a sinusoidal EMF, a distributed winding, and is controlled by continuous vector FOC using an encoder — typical applications are EV traction motors, turbochargers, CNC, and aviation.
Before discussing BLDC motors separately, let us untangle the terms. In Russian-language engineering literature — and, even more so, in marketing materials — BLDC and PMSM are often used as synonyms, which is incorrect. These are two distinct classes of electric machine with the same structural basis (a stator with a three-phase winding plus a rotor with permanent magnets) but a fundamentally different operating mode and control type.
| Parameter | BLDC (Brushless DC) | PMSM |
|---|---|---|
| Back-EMF waveform | Trapezoidal | Sinusoidal |
| Phase-current waveform | Rectangular 120° blocks | Sinusoid |
| Commutation algorithm | Block commutation, six-step | Field-Oriented Control (FOC), continuous |
| Position feedback | Hall sensors (3) or sensorless via EMF | Encoder / resolver / model-based sensorless |
| Winding type | Concentrated | Distributed |
| Magnet geometry | Surface-mounted (SPM) | Interior (IPM) or Halbach |
| Torque ripple | 5-15% (characteristic cogging) | Below 1% |
| Acoustic noise | Noticeable "whining" tone at commutation transitions | Low |
| Typical efficiency | 85-92% | 92-97% |
| Typical applications | Drones, household appliances, simple servo drives | EV traction, turbomachinery, CNC, aviation |
Structurally these machines are nearly identical — the same copper, the same magnets, similar magnetic cores. The whole divide lies in the field waveform and the inverter type. A distributed winding with the correct overlap of pole arcs gives a sinusoidal EMF → the motor is controlled by FOC → it is a PMSM. A concentrated winding with surface magnets gives a trapezoidal EMF → the motor is controlled by block commutation from a simple ESC → it is a BLDC.
Why e-turbo and e-compressor are in section 3 rather than here. The BorgWarner 48V eBooster, Garrett Motion E-Turbo, Mitsubishi Electric FCEV compressor, and MAHLE Powertrain e-compressor are all PMSM by construction: distributed winding, interior-magnet rotor, FOC with vector modulation, a fundamental frequency of 5-15 kHz, with litz wire removing AC losses to the level of R_AC/R_DC = 1.1-1.3. They work on the same physical principles as EV traction motors and aircraft propulsion machines — only in a different power and speed range. That is why the "high-speed PMSM" group brings them together.
Why drone motors and medical pumps are in this section. The T-Motor MN505-S, DJI Matrice 300 RTK, Tarot Pro 4120, Abbott HeartMate 3, and Abiomed Impella are classic BLDC: concentrated winding, surface-mounted magnets, control via an ESC with six-step commutation or a simplified FOC on STM32/ESP32-class controllers. The fundamental frequency is a few kilohertz, the ESC switching frequency 10-50 kHz. The physics is quite different, and the benefit of litz wire is of a different nature too — not fighting AC losses at the fundamental frequency, but reducing the heat generation from ESC harmonics.
Where the boundary blurs. Modern drone ESC controllers (Flipsky FSESC, VESC Mkx, T-Motor ALPHA) already support an FOC mode. The same T-Motor MN505-S, running through an FOC-ESC on a professional-class quadcopter, is already a de facto PMSM rather than a BLDC. Over the past five years the boundary between the classes has shifted toward FOC, and in the coming years the term BLDC will probably remain only for simple ESC drives with Hall sensors.
Having sorted out the classification, we turn to where litz wire in the windings of these motors delivers a measurable gain.
5.1 Stepper motors: microstepping and heating
A classic NEMA 17 or NEMA 23 stepper motor runs at low speeds (a few revolutions per second) and relatively low switching frequencies (up to 1 kHz with standard drivers, up to 50 kHz in chopper-based microstepping modes). One would think ordinary 0.3-0.5 mm enamelled wire would cope. And indeed, in most stepper motors it does.
It gets interesting in two cases.
Precision microstepping mode. Modern drivers (Trinamic TMC5160, Trinamic TMC2209, Analog Devices AMC7926) run a chopper up to 50 kHz, supplying the winding with a PWM current of sinusoidal envelope. The PWM edges are a few nanoseconds. As a result, harmonics up to several hundred kilohertz are present on the winding. At medium-to-high motion speeds this causes noticeable AC losses, which turn into heat in the motor housing. For a motor operating in a vacuum chamber or a sealed precision drive, every extra watt becomes a heat-removal problem. Specific applications where this is critical:
- Semiconductor lithography lines (ASML, Nikon) — nanometer positioning, vacuum chamber.
- AFM and STM systems (Bruker, Oxford Instruments) — tip positioning with sub-atomic precision.
- Medical radiotherapy systems (Elekta Versa HD, Varian TrueBeam) — positioning the proton-beam collimator.
- Precision manipulators by Mitsubishi, Yaskawa — for microelectronics assembly.
Litz wire with 0.07-0.1 mm strands removes AC losses by 30-50% and lets the motor run cooler at the same load. A typical grade for such applications is Litz PET 100×0.1 or Litz 200 PI 150×0.07 for especially sensitive tasks.
High-precision instrument stepper motors. Special models are produced in series with litz-wire windings:
- Lin Engineering Silverpack SP57 — NEMA 23 with a litz-wire winding, 2 N·m, specifically for medical/industrial use.
- Nanotec SCA2023 — NEMA 23 with a litz-wire option, for high-frequency microstepping.
- Oriental Motor AlphaStep AZ — a Japanese precision line, litz wire in the premium models.
The measured effect: a litz-wound motor shows 10-15% more torque at the same winding temperature compared with enamelled wire (data from a Lin Engineering technical bulletin, 2023).
5.2 Brushless DC motors (BLDC)
BLDC is a huge category, from quadcopter motors (10-50 kHz ESC) to high-speed industrial drives. Litz wire is used where high frequency and a high loss level with plain enamelled wire coincide.
Commercial-class drones and UAVs. The paper "Penerapan Kawat Litz Pada Motor BLDC Untuk Peningkatan Gaya Dorong Per Daya" (ResearchGate, 2024) is a direct measurement on a propeller rig. The winding resistance with litz wire is 0.38 ohm versus 0.43 ohm for enamelled wire (same copper), with a corresponding reduction in copper loss at full throttle. For a drone with a 30-minute flight time this gives an additional 2-3 minutes of flight at the same battery capacity — a practically significant result for commercial tasks.
Medical equipment. Brushless motors in medical devices operate under conditions where excess heat generation can disrupt the process: Abbott HeartMate 3, Abiomed Impella CP, Medtronic HVAD, Baxter AK-98, Fresenius 4008. A typical grade for medical BLDC is Litz PI 100×0.1 (polyimide for chemical and thermal stability during sterilization) or Litz F for pumps in contact with aggressive media (dialysis solutions, saline).
6. What changes in the manufacturing process of a litz-wound motor
Switching from enamelled wire or hairpin to litz wire is not just a material substitution. It is a change in the winding and acceptance process.
Winding. Litz wire is softer than round enamelled wire of the same cross-section — this gives more freedom in laying it down, but requires care with tension. Too much tension flattens the bundle; too little, and the turns lie loosely, losing fill density. Modern winding-shop machines — Marsilli M530 / M540, Meteor-Elektronika-Zipper MW-4000, Aumann Limbach MaxE, RWTH Aachen PEM Statomat — have dedicated tension modes for litz wire with wire-force feedback.
End termination. For class F grades with self-bonding enamelled wire, the strands are tinned en masse by dip-tinning the end of the bundle in solder at 380-400 °C. Equipment — AMTech SolderMate (USA) or ETMA DIP (Germany). For class 200 on PAI varnish this trick does not work — it requires either laser cleaning (equipment TRUMPF TruMicro Series 2000, Coherent HighLight FL-ARM — adopted in Russian production from 2023), or chemical stripping with a solvent, or friction-mechanical stripping.
Vacuum pressure impregnation. A litz-wire winding is more "open" than a solid-wire one — there are voids between the strands. During vacuum impregnation (equipment Elantas Elmotherm VPI, Von Roll Samicatherm) the compound penetrates inside the bundle and bonds the strands together with the varnish. This matters for three reasons. First, micro-air-gaps are eliminated — the gaps where partial discharges ignite under inverter supply. Second, the winding's thermal conductivity improves (the copper is bonded to the structure through the compound rather than through air). Third, the winding mechanically locks into a single mass and withstands the centrifugal loads of high-speed rotors.
This is exactly why, in my article on choosing a litz-wire grade, I specifically stressed the importance of adhesion to compounds (PET and multifilament Arselon/PP wet out excellently; PTFE does not wet at all). In motor manufacturing this is not a theoretical parameter but the basis of the finished motor's reliability.
Quality control. For series production of litz-wound motors, an additional acceptance parameter appears — measuring RAC at the operating frequency. The DC resistance of a litz winding is indistinguishable from a single-wire one of the same cross-section, but the AC resistance at the target inverter frequency is exactly what you paid for when ordering litz wire. Modern impedance analyzers (Keysight E4990A 20 Hz - 120 MHz, Hioki IM3590 40 Hz - 200 kHz, Zurich Instruments MFIA 1 µHz - 5 MHz) allow RAC to be measured in a band up to 10 MHz with 0.5% accuracy. For acceptance against a spec, this is the instrument that separates a winding "made of litz wire that worked as intended" from one "made of litz wire but with the transposition disrupted during winding" — cases that are externally indistinguishable.
Summary: where litz wire is used in electric motors today
Five classes of application where litz wire in motor windings delivers a measurable gain and has already become an industrial standard or is rapidly becoming one:
- EV traction motors — in hybrid hairpin+litz configurations (MDPI Electronics 2025: +1.5-2% efficiency on WLTP) or in formed litz windings of the Formed Litz type (RWTH Aachen + Schaeffler).
- High-speed PMSM — e-turbo, e-compressor at 100,000-200,000 rpm (hofer/Pankl, Lee et al. 2023), airgap windings in coaxial prototypes.
- Aircraft motors — MEA systems on the 787/A380 and 1 MW-class electric-aircraft propulsion motors (IEEE 2024, Fraunhofer Project AMBER).
- Stepper motors — precision drives with litz-wire windings (Lin Engineering, Silverpack), vacuum and medical applications.
- BLDC — drones with extended flight time, medical pumps, precision drives.
In each of these classes we produce litz wire: for EV — mostly rectangular cross-sections of 2:1...3:1 in class F or 200 with a PET/polyimide jacket; for high-speed PMSM — round litz with thin strands (0.071-0.1 mm) in polyimide; for aviation — custom class 200 configurations with a combined PTFE/Arselon jacket; for steppers and BLDC — most often standard round catalog positions. The choice of a specific grade is discussed separately for each application — the long article on selection contains the full procedure, and the calculator gives a first approximation for your frequency and current.
If you are designing a motor in any of the five classes, send us the operating point (inverter frequency, rotor speed, phase current, slot-window geometry) along with your weight/efficiency/temperature requirements. We will compute a configuration, propose a grade, and if needed make a trial run. On particularly interesting motor tasks — aviation, new engine types, non-standard configurations — we are prepared to make trial batches at our own expense, in exchange for the option to include the results, anonymized, in our publication base.
References
- Shevyreva A., Wang Y. et al. Design Analysis of an Interior Permanent Magnet Synchronous Motor with Hybrid Hair-Pin and Litz Wire Windings. MDPI Electronics, vol. 14, no. 17, 3350, 2025.
- Winding Loss Suppression in Inverter-Fed Traction Motors via Hybrid Coil Materials and Configurations. Applied Sciences (MDPI), vol. 13, no. 20, 11429, 2023.
- Ji Y., Giangrande P., Zhao W., Madonna V., Zhang H., Galea M. Inverter-Fed Electrical Machines Exposed to Prevailing Electrical Stress. IEEE Trans. Aerosp. Electron. Syst., vol. 59, no. 9, pp. 9368–9378, 2023.
- Born H.C., Keller A., Baumann M., Heine M., Mertens A. Manufacturing Process and Design Requirements of Litz Wire with Focus on Efficiency Improvement of Traction Motors. 12th International Electric Drives Production Conference (EDPC), Regensburg, 2022.
- Development of a Production Process for Formed Litz Wire Stator Windings. RWTH Aachen University + Schaeffler, ResearchGate ID 366408980, 2022.
- Optimization and Comparison of 1 MW-Class PM Motors for Aircraft Propulsion Using Litz Wire and Hairpin Windings. IEEE Xplore document 10908992, 2024.
- Lee G.-H., You Y.-M. Performance Validation of High-Speed Motor for Electric Turbochargers. MDPI Electronics, vol. 12, no. 13, 2937, 2023.
- Zhang X., Bowman C., O'Connell T., Haran K., Jones W. Large Electric Machines for Aircraft Electric Propulsion. IET Electric Power Applications, vol. 12, no. 6, pp. 767–779, 2018.
- Cao W., Mecrow B.C., Atkinson G.J., Bennett J.W., Atkinson D.J. Overview of Electric Motor Technologies Used for More Electric Aircraft (MEA). IEEE Trans. Ind. Electron., vol. 59, no. 9, pp. 3523–3531, 2012.
- Litz Wire Strand Shape Impact Analysis on AC Losses of High-Speed PMSM. IEEE Xplore document 9425656, 2021.
- Comparative Analysis of AC Losses with Round Magnet Wire and Litz Wire Winding of a High-Speed PM Machine. IEEE Xplore document 8922173, 2019.
- Arruti A., Aizpuru I. et al. Evolution of Classical 1-D-Based Models for Litz Wire Losses. IEEE Trans. Power Electron., vol. 39, 16371, 2024.
- Penerapan Kawat Litz Pada Motor BLDC. ResearchGate, 2024.
- Charged EVs. hofer and Pankl develop integrated e-turbo system, Chargedevs.com, October 2025.
- Electric aircraft motor achieves 1,000 hp with 207 pound weight. Fraunhofer Project AMBER, October 2025.
- US Patent 11942842. Compressed motor winding. USPTO, 2024.
- Ionel D.M. Cryogenic Thermal System for Coreless Axial Flux PM Machine with Litz Wire Winding for Electric Aircraft Propulsion, 2021.