August 12, 2025

The global shift toward energy efficiency, precision control, and reduced maintenance costs has accelerated the adoption of Electronically Commutated (EC) centrifugal fans across industries. At the heart of these fans is the Brushless DC (BLDC) motor, a technology that merges the electrical efficiency of DC operation with the convenience of AC mains connectivity through integrated electronics. While centrifugal fans have long been powered by traditional AC induction motors, the introduction of BLDC motors into fan design has transformed performance possibilities. EC centrifugal fans now offer superior energy efficiency, lower noise, precise airflow control, and extended service life—attributes directly linked to BLDC technology. What is an EC Centrifugal Fan? An EC centrifugal fan is a fan that uses a brushless DC motor powered by an integrated electronic control module. The “electronically commutated” part means that instead of using mechanical brushes and a commutator to switch current in the rotor windings, the switching is done electronically via a control circuit. Key Points: Power Input: EC fans are connected to standard AC mains (single-phase 110–240V or three-phase 380–480V). Motor Operation: Internally, AC is rectified to DC and supplied to the BLDC motor windings. Speed Control: Controlled by pulse-width modulation (PWM), 0–10V analog signal, or digital protocols like Modbus or BACnet. Airflow Generation: The centrifugal impeller accelerates air radially outward, creating a pressure rise for ducted systems. Inside the BLDC Motor A Brushless DC motor inside an EC fan consists of: Stator – Laminated steel core with copper windings, forming the stationary part of the motor. Rotor – Permanent magnets mounted on a shaft, replacing rotor windings found in AC induction motors. Position Sensors – Detection of rotor position using Hall-effect sensors or through sensorless control algorithms. Electronic Controller (ECU) – Rectifies AC to DC, manages commutation, regulates speed, and controls torque. Rotor Uses rare-earth permanent magnets (typically NdFeB) for high magnetic flux density. No rotor copper windings → eliminates rotor I²R losses. Light rotor reduces rotational inertia for faster speed changes. Stator Wound with enamelled copper wire. Optimized slot fill factor for higher efficiency. Often designed with skewed slots to reduce cogging torque. Commutation Performed electronically rather than mechanically. Switches current in windings in sync with rotor position to maintain torque production. Two main methods: trapezoidal (block) commutation and sinusoidal commutation. Trapezoidal: Simple, good for cost-sensitive applications. Sinusoidal: Smoother torque, lower noise, ideal for HVAC fans. How BLDC Motors Work in EC Fans Power Conversion Path AC Input: From mains power supply. Rectification: AC is converted to DC using a diode bridge or rectifier. DC Bus: Filters and capacitors smooth DC voltage. Inverter Stage: High-speed switching (MOSFETs or IGBTs) generates 3-phase AC for the BLDC motor. Electronic Commutation: Controller adjusts phase timing based on rotor position feedback. Output Control: Matches fan speed to required airflow or pressure setpoint. Why BLDC Motors Excel in EC Centrifugal Fans Efficiency BLDC motors achieve 80–90% efficiency compared to 60–75% for equivalent AC induction motors. Reduced rotor losses and optimized winding design. Speed Control Smooth variable-speed control from 20% to 100% of rated speed. High part-load efficiency—important for HVAC systems with variable airflow demands. Noise Reduction Sinusoidal commutation minimizes torque ripple. Precise control reduces mechanical vibration and aerodynamic noise. Compactness Higher torque per volume allows smaller motors for the same output. Eliminates bulky external VFDs by integrating control electronics. Performance Comparison: AC Induction vs BLDC in Centrifugal Fans Parameter AC Induction Motor Fan BLDC Motor EC Fan Motor Efficiency 60–75% 80–90% Speed Control Range Limited without VFD Wide (integrated control) Torque at Low Speed Reduced Maintained Heat Generation Higher Lower Noise Level Higher at part load Lower due to smoother commutation Maintenance Bearings only Bearings only Power Factor 0.6–0.85 >0.95 Design Considerations for BLDC Motors in EC Fans Motor Sizing Must handle peak torque during startup and transient load changes. Oversizing slightly can improve thermal performance and extend lifespan. Thermal Management BLDC motors generate less heat, but integrated electronics require cooling. Common methods: heat sinks on controller housing, forced airflow from impeller. Magnet Selection NdFeB offers highest performance but can lose magnetism at high temperatures (>150°C). For high-heat applications, SmCo magnets may be used. Control Algorithms Field-Oriented Control (FOC) for optimal torque and efficiency. Sensorless control for lower cost, but Hall sensors often preferred for high reliability in HVAC. Integration with Fan Aerodynamics BLDC motors enable new aerodynamic optimizations in EC centrifugal fans: Direct-drive design eliminates belts and pulleys, improving mechanical efficiency. Lower rotor inertia allows adaptive speed changes to meet real-time airflow demands. Integration with variable inlet vanes or EC impeller blades for peak performance. Application Commercial HVAC Systems Fans for supply and return airflow in air handling units Demand-controlled ventilation with CO₂ or occupancy sensors. Data Centers Precise temperature and pressure control for server room cooling. EC fans integrated into Computer Room Air Conditioning units. Refrigeration and Cooling Towers Variable-speed fans reduce energy use during cooler ambient conditions. Improved defrost cycles. Cleanrooms & Laboratories Low-noise, precision airflow for controlled environments. Energy Savings Example Consider a 5 kW centrifugal fan running 6,000 hours/year: AC Induction Fan Efficiency: 70% Input = 7.14 kW Annual Energy Use = 42,840 kWh BLDC EC Fan Efficiency: 88% Input = 5.68 kW Annual Energy Use = 34,080 kWh Savings: 8,760 kWh/year (~$1,050/year at $0.12/kWh) CO₂ Reduction: ~6.2 metric tons/year (based on 0.7 kg CO₂/kWh grid emission factor) Reliability and Maintenance No brushes → no brush wear, less downtime. Bearings remain the only major wear component. Electronics are designed for 40,000–60,000 hour lifespans but require protection from moisture and surges. Industry Standards and Compliance BLDC-powered EC fans often meet or exceed: EU ErP Directive for fan efficiency. US DOE Fan Energy Index (FEI) requirements. ISO 5801 (airflow performance testing). IEC 60034-30-2 for motor efficiency classification. Future Trends Wide Bandgap Semiconductors (SiC, GaN): Improve inverter efficiency and reduce controller size. Sensorless High-Precision Control: For cost and reliability improvements. IoT Integration: Remote monitoring, predictive maintenance, real-time optimization. The Brushless DC motor is the technological backbone of EC centrifugal fans, delivering unmatched efficiency, control precision,

Centrifugal fans serve HVAC, industrial ventilation, clean rooms, electronics cooling, and various air-moving uses. They move air radially, changing its direction by 90 degrees and increasing its pressure. Traditionally, AC centrifugal fans—powered by alternating current induction motors—were the standard choice. However, in the last decade, EC (Electronically Commutated) centrifugal fans, which integrate a brushless DC motor with onboard electronics, have emerged as a high-efficiency alternative. Choosing between EC and AC centrifugal fans involves balancing performance, efficiency, cost, and application requirements. This article examines their differences in depth, providing data, examples, and recommendations. AC Centrifugal Fans Driven by asynchronous induction motors powered directly from the AC mains. Speed is determined by supply frequency (50 Hz or 60 Hz) and motor pole count. Speed control requires additional devices (e.g., VFDs or voltage regulators). Key Features: Simple, robust design. Long-established technology. Lower initial cost. EC Centrifugal Fans Use brushless DC motors with integrated AC-to-DC conversion electronics. Speed control is built-in and managed electronically. Motor commutation is handled via microprocessor-controlled electronics. Key Features: Higher efficiency. Integrated speed control. Precise airflow management. How They Work Feature AC Centrifugal Fan EC Centrifugal Fan Motor Type Induction motor (single or three-phase) Brushless DC motor with integrated electronics Power Supply Direct AC AC converted to DC internally Speed Control External (VFD, voltage regulator) Integrated electronic control Efficiency 50–70% (typical) 80–90% (typical) Maintenance Minimal, but higher wear over long term Very low, fewer wear parts Efficiency and Energy Consumption AC centrifugal fans have limited efficiency due to: Rotor slip losses in induction motors. Fixed speed operation. Lower power factor at partial load. EC centrifugal fans: Use permanent magnets → no rotor slip losses. Operate with variable speed and optimized control algorithms. Provides excellent efficiency across a wide range of operating conditions. Table 1: Typical Efficiency Comparison Motor Power (kW) AC Fan Efficiency (%) EC Fan Efficiency (%) 0.5 60 82 1.0 65 85 2.0 68 88 5.0 70 90 Energy Savings Example Consider a 2 kW fan running 4,000 hours/year: AC fan: 2 kW × 4,000 h ÷ 0.68 efficiency = 11,764 kWh/year EC fan: 2 kW × 4,000 h ÷ 0.88 efficiency = 9,091 kWh/year Annual Savings: 2,673 kWh/year, which could translate to $300–$500/year depending on electricity rates. Speed Control and Airflow Management AC Fans Speed changes require frequency inverters (VFDs) or voltage controllers. Each method adds cost and may introduce harmonic distortion. Mechanical dampers are an option but waste energy. EC Fans Built-in electronic control allows speed adjustment via: 0–10V control signal PWM signal Modbus or BACnet communication Allows dynamic adjustment for demand-based ventilation, leading to significant energy savings. Noise Performance AC fans operate at fixed speed, often generating more noise during low demand periods since airflow cannot be reduced without throttling. EC fans reduce noise by slowing down during partial load, cutting sound levels significantly. Table 2: Example Noise Levels Operating Mode AC Fan Noise (dB(A)) EC Fan Noise (dB(A)) Full Speed 75 74 70% Speed 75 (throttled) 66 50% Speed 75 (throttled) 60 Maintenance and Reliability AC Fans Consistent performance under tough industrial conditions. Bearings require periodic inspection/lubrication. Motor winding insulation can degrade over decades. EC Fans Fewer mechanical wear parts (no brushes). Electronics are the main wear point—quality design is crucial. Often have longer service intervals but can be more complex to repair. Cost Considerations Initial Purchase Cost AC centrifugal fans: 20–40% lower upfront price. EC centrifugal fans: Higher due to integrated electronics and permanent magnet motors. Lifetime Cost When factoring in energy savings and maintenance, EC fans often have a lower total cost of ownership (TCO). Example ROI Calculation (2 kW fan): AC Fan Cost: $1,000 EC Fan Cost: $1,400 Annual Energy Savings: $350 Payback Period: (1,400 – 1,000) ÷ 350 ≈ 1.14 years Environmental Impact EC fans contribute to: Lower CO₂ emissions due to reduced energy use. Compliance with efficiency regulations like EU Ecodesign Directive (ErP) or U.S. DOE fan efficiency rules. Applications and Suitability AC Fans: Best For Heavy-duty industrial settings where speed variation is not critical. Harsh environments where electronics may fail prematurely. Budget-sensitive projects. EC Fans: Best For Commercial buildings requiring variable air volume (VAV) control. Data centers, cleanrooms, and laboratories where precise airflow is critical. Energy-efficient retrofits to meet green building standards. Comparative Summary Table Factor AC Centrifugal Fan EC Centrifugal Fan Efficiency 50–70% 80–90% Speed Control External device required Integrated Noise Control Limited Excellent at partial load Maintenance Low to medium Low Initial Cost Low Higher TCO Higher (over lifetime) Lower (energy savings) Best Use Case Fixed-speed, industrial Variable-speed, efficiency-driven Real-World Example: Data Center Ventilation Upgrade A data center replaced 20 × 2 kW AC centrifugal fans with EC versions: Energy savings: 2,673 kWh/year/fan → 53,460 kWh/year total Annual cost savings: ~$8,000 (at $0.15/kWh) CO₂ reduction: ~25 metric tons/year Payback: 1.5 years Decision-Making Framework When choosing between EC and AC centrifugal fans, consider: Operating Hours – High operating hours favor EC fans for ROI. Airflow Variability – If demand fluctuates, EC offers more control and savings. Budget Constraints – AC may be better for short-term, low-cost installations. Environment – Harsh, high-temperature environments may still favor AC fans unless EC is specifically designed for such conditions. Regulatory Requirements – EC fans may be necessary to meet modern efficiency standards. Both EC and AC centrifugal fans have valid applications: AC fans remain reliable, cost-effective choices for fixed-speed, rugged industrial environments. EC fans shine in energy efficiency, noise reduction, and precision airflow control, making them ideal for commercial, residential, and high-tech facilities. If energy costs are significant and variable airflow is required, EC centrifugal fans almost always offer a better long-term investment. However, in cost-sensitive, fixed-speed industrial environments, AC centrifugal fans can still be the practical choice.

Axial flux motors (AFMs) offer exceptional torque density, a compact form factor, and high efficiency, making them ideal for electric vehicles, aerospace, industrial automation, robotics, and renewable energy applications. A critical design parameter in AFMs is the winding configuration—how the copper coils are arranged around the stator. Two dominant approaches are: Distributed winding (also known as lap winding or distributed armature winding) Concentrated winding (also called tooth-coil winding) The choice between these winding techniques has profound implications on: Motor efficiency Torque ripple Manufacturing complexity Thermal management Cost and weight Axial Flux Motor Winding In an axial flux motor: The stator contains coils that produce an alternating magnetic field when energized. Permanent magnets on the rotor interact with the field to generate torque. Unlike radial flux motors, axial flux motors feature a flat, disc-shaped design, with coil placement optimized for magnetic flux flowing axially.The winding configuration determines: Slot fill factor (how efficiently copper occupies slot space) Inductance and resistance of the coils Magnetic flux distribution Thermal dissipation efficiency Distributed Winding in Axial Flux Motors Definition In distributed winding, the coils are spread over multiple stator slots per pole per phase. Each phase winding is distributed across several slots, resulting in overlapping coil sides. Example: For a 12-slot, 10-pole motor, a phase winding may span several slots in a wave-like pattern. Characteristics Produces a sinusoidal magnetomotive force (MMF) distribution, reducing harmonic content. Higher copper usage compared to concentrated winding. More complex coil insertion and end-winding design. Advantages Low harmonic distortion → minimizes eddy current loss within the rotor magnets Lower torque ripple → smoother operation. Better efficiency at high speed due to reduced core loss from harmonics. Disadvantages Longer end windings → higher copper losses (I²R losses). Heavier and bulkier due to more copper. More complex manufacturing and winding insertion process. Concentrated Winding in Axial Flux Motors Definition In concentrated winding, each coil is wound around a single tooth or stator pole. The coil sides are concentrated on one tooth rather than distributed over several. Example: For a 12-slot, 10-pole motor, each tooth carries one complete coil. Characteristics Produces a more trapezoidal MMF waveform, increasing harmonic content. Shorter end windings, reducing copper length and weight. Easier manufacturing and coil replacement. Advantages Higher slot fill factor → better thermal dissipation and compact design. Lower copper usage → reduced resistance, less I²R loss. Simpler winding process → suitable for automated manufacturing. Disadvantages Higher torque ripple due to harmonic components. Higher AC copper losses at high speeds from increased harmonic currents. Requires additional design measures to control eddy current loss in magnets. Key Performance Metrics: Distributed vs Concentrated Table 1: Comparison of Distributed and Concentrated Winding in Axial Flux Motors Parameter Distributed Winding Concentrated Winding MMF waveform Sinusoidal (low harmonics) Trapezoidal (high harmonics) Torque Ripple Low Higher Copper Usage Higher (longer end windings) Lower (shorter end windings) Slot Fill Factor Medium High Efficiency at High Speed Higher Lower (due to AC losses) Manufacturing Complexity High Low Weight Higher Lower Thermal Management More challenging (dense winding) Easier (compact coil on single tooth) Cost Higher Lower Electromagnetic Impact of Winding Choice Harmonics and Losses Distributed winding minimizes slot harmonics, reducing iron and eddy current losses in rotor magnets. Concentrated winding increases harmonic content, leading to higher eddy currents, especially in surface-mounted permanent magnets. Efficiency Trends Test data for a 5 kW axial flux prototype: Winding Type Peak Efficiency (%) Torque Ripple (%) Copper Loss (W) Core Loss (W) Distributed 95.2 2.5 140 60 Concentrated 94.1 5.8 110 85 Thermal Management Considerations Distributed Winding More copper per slot → higher thermal mass, but longer end windings can be harder to cool. Requires advanced cooling: forced-air or liquid cooling channels in the stator. Concentrated Winding Shorter end windings and compact coils make cooling more direct. Easier to integrate direct winding cooling (DWC) systems. Manufacturing and Cost Implications Distributed Winding More labor-intensive due to overlapping coil placement. Ideal for limited runs prioritizing performance over cost Concentrated Winding Easier to automate with pre-formed coils. Preferred in mass production applications like electric two-wheelers, drones, and some EV motors. Application-Specific Recommendations Application Recommended Winding Reason High-performance EV traction Distributed High efficiency, low torque ripple Light electric vehicles (e-bikes) Concentrated Cost-effective, compact, easy to produce Aerospace actuators Distributed Precision motion, low noise Drones & UAVs Concentrated Lightweight, high torque-to-weight ratio Industrial automation Distributed Smooth motion, reduced mechanical vibration Portable tools Concentrated Low cost, simplified manufacturing Design Optimization Strategies For Distributed Winding: Use fractional-slot winding to further minimize torque ripple. Employ skewed slots to reduce cogging torque. Optimize end-winding shape to reduce copper loss. For Concentrated Winding: Apply magnet segmentation to reduce eddy current loss from harmonics. Use high-resistivity magnet materials (e.g., NdFeB with Dy additions). Incorporate fractional-slot concentrated winding (FSCW) to balance harmonic suppression and compactness. Case Study: EV Axial Flux Motor Motor Specs: Power: 100 kW Diameter: 320 mm Cooling: Liquid Distributed Winding Design: Efficiency: 96.2% peak Torque ripple: 1.8% Manufacturing cost index: 1.4 Concentrated Winding Design: Efficiency: 94.9% peak Torque ripple: 4.5% Manufacturing cost index: 1.0 For premium EVs, distributed winding is chosen for its smoothness and efficiency. For budget EVs, concentrated winding offers competitive performance at lower cost. The choice between distributed and concentrated winding in axial flux motors depends on performance priorities, cost constraints, and application needs: Distributed winding: Best for applications needing high efficiency, low torque ripple, and smooth operation, though at higher manufacturing cost. Concentrated winding: Ideal for cost-sensitive, lightweight, and compact designs, especially in mass production. Future innovations—like fractional-slot distributed winding and segmented magnet designs—are helping bridge performance gaps, allowing engineers to tailor winding configurations more precisely to application requirements.

Axial flux motors (AFMs), also known as pancake motors, offer distinct advantages over their radial flux counterparts—including high power density, compact form, and efficient thermal management. Central to their performance are magnet configurations, particularly in single-rotor and double-rotor designs. Understanding differences in magnetic layout, flux behavior, performance metrics, and trade-offs is essential to choosing the optimal configuration. Axial Flux Motor Basics Axial flux motors generate electromagnetic torque via interaction between permanent magnets (usually rare-earth) on a disc-shaped rotor and windings on a stator, typically sandwiching one or more rotor discs. Characteristics include: Compact axial length — resulting in higher torque density (Nm per liter) Short magnetic flux path — reduces magnetic losses and enables high efficiency Surface- or interior-mounted magnets — affects flux penetration and mechanical protection Magnet configurations influence: Flux density in the air gap (B_g) Cogging torque Thermal performance Mechanical complexity Key magnet layout types: Surface-Mounted Permanent Magnets (SPM) Interior Permanent Magnets (IPM) Halbach arrays (a specialized SPM array enhancing one-sided flux) Single Rotor Configuration In this design: One rotor disc bears magnets, typically facing a stator on one side. Commonly arranged as rotor–stator–[air gap]–housing. Magnetic Behavior Flux crosses a single air gap. Magnetic circuit simpler: one stator–rotor interface. Ease of manufacturing and assembly. Performance Characteristics Cogging Torque: Present; design mitigations like skewing or fractional slot winding help. Efficiency: High, but slightly lower than double-rotor due to single-sided flux utilization. Thermal Management: Easier—stator and windings accessible. Use Cases E-bikes, drones, appliances, low-cost industrial motors. Applications where thickness must remain minimal. Advantages Disadvantages – Simple design – Easier cooling – Lower cost – Lower torque density – One-sided flux only Double Rotor Configuration Two rotor discs, each with magnets, sandwich the stator in a rotor–stator–rotor (R–S–R) arrangement. Essentially, two flux paths operate in parallel. Magnetic Behavior Dual air gaps: one between each rotor and stator. Flux splits across two gaps; ideally symmetric to maximize utilization. Magnetic flux density can be higher for same magnet volume. Performance Characteristics Torque Density (T_d): Generally higher than single rotor, due to doubled interacting surface. Torque Calculation: Approximate torque scales near 2× single rotor (minus minor leakage losses). Cogging Torque: Can be reduced if rotor magnet poles are offset relative to each other or stator. Efficiency: Improved electrical-to-mechanical conversion due to better flux utilization. Complexity: Higher—requires supporting two rotors; mechanical alignment critical. Thermal Management: Slightly more complex due to sandwiched stator; but heat can flow from both sides to cooling surfaces. Use Cases Automotive traction motors (EVs/hybrid systems) Heavy-duty industrial drives Applications demanding high torque in limited axial space Advantages Disadvantages – Higher torque density – Better efficiency – Lower cogging – Higher cost – Complex alignment – Harder cooling Quantitative Comparison Below is a hypothetical comparative table based on typical small to medium-sized axial flux motors (e.g., 10 kW class), illustrating key metrics: Parameter Single Rotor (SR) Double Rotor (DR) Air Gap Count 1 2 Magnet Volume (V_magnets) 1 unit ~1.8–2 units* Peak Torque (Nm) 50 90 Torque Density (Nm/L) 45 80 Cogging Torque (% of T_peak) 5% 3% Efficiency (%) 93 95 Axial Length (mm) 100 150 Structural Complexity Low Medium-high Thermal Access Excellent Moderate Estimated Cost Index 1.0 1.3 (due to parts & assembly) DR requires more magnet material, but improved magnetic utilization may allow using slightly less per rotor than SR per rotor. Notes on Data: Magnet Volume: A double-rotor design uses more magnets, but each rotor can be slightly thinner if the flux paths share better, sometimes resulting in ~1.8× rather than a full 2× increase. Torque Density: DR yields ~1.8× to 2× the torque, reflecting two active faces. Cogging: Offset magnet arrangement mitigates torque ripple better in DR. Efficiency: Gains derive from reduced magnetic leakage and better utilization—typically 1–2 percentage points. Axial Length: DR is thicker, impacting form factor. Cost: Higher due to more rotor parts, dual bearings, more complex assembly. Design Considerations and Trade-offs Magnet Usage & Material Cost Rare-earth magnets (e.g., NdFeB) dominate cost. DR uses more magnets, increasing cost—but higher performance may justify it. Designers often balance magnet grade (remanence, coercivity) and volume. Mechanical Complexity SR: single shaft and rotor assembly, simpler bearings and alignment. DR: requires two rotors, careful axial concentric alignment, often double bearings or a thrust bearing. Structural Support & Stiffness DR’s additional rotor adds weight and potential flex. Housing must be robust to sustain torque and axial forces. Cooling & Thermal Path SR: stator typically on exterior, easy to cool. DR: stator is in the middle—an internal stator requires heat paths both sides, often using cooling plates or fluid channels. Magnetic Design Complexity Flux cancellation and leakage must be controlled. Cogging reduction strategies: skewing, fractional slots, magnet angular offset (especially effective in DR by anti-phase rotor placement). Control Strategy Both use typical control (e.g., field-oriented control), but DR may have symmetric inductance profiles aiding smoother control. Applications and Case Examples Electric Vehicles and Traction Double Rotor AFMs excel where axial space exists (e.g., between output shaft and chassis). Example: A 50 kW DR AFM used in an EV delivers high torque density—peak 300 Nm in a 180 mm thick motor pack. Aerospace and Drones Single Rotor AFMs favored in lightweight, thin packages (e.g., propeller-driven drones). Example: A 5 kW pancake motor, diameter 200 mm, axial length 60 mm, weighing 2 kg—suitable for multicopter propulsion. Industrial Automation Both types used for servo motors or direct-drive applications. DR proves advantageous in limited axial envelope but high torque need (e.g., robotic joints). Simulated Performance Modeling Consider two simulated 20 kW motors for a robotics application: SR Model: Diameter: 250 mm Axial length: 90 mm Magnet volume: 0.005 m³ equivalent Simulated flux density (B_g): 0.8 T Peak torque: ~200 Nm Estimated efficiency: 93% DR Model: Same diameter Axial length: 140 mm Magnet volume: 0.0085 m³ equivalent Simulated B_g per side: 0.75 T Peak torque: ~350 Nm Estimated efficiency: 95% Key insights: DR achieves about 1.75× torque increase for ~1.7× magnet volume increase. Efficiency gain of ~2 points likely due to improved flux utilization and