Echoing, in this editor’s mind, the collaboration between Oxford University and YASA motors, a recently announced motor from Belgium’s Ghent University and Magnax, makers of what they term an “axial flux machine.” Similar to YASA’s products, the motors are yokeless, which the makers claim promotes lower weight and the shortest possible flux path.
Beyond this feature, the motor/generators offer “A patented system for cooling the windings, for the lowest possible stator temperatures.” According to Magnax, their Dual permanent magnet rotors give “the highest possible torque-to-weight ratio.” Rectangular section copper wire fills more area than round wire and concentrated windings allow “the lowest possible copper losses (no coil overhangs).” Grain-oriented electric steel lowers “core losses by as much as 85-percent.”
The company’s white paper gives graphic and written explanations as to why these factors enable the Magnax motors to achieve 96-percent efficiency. While the company compares their motors to large, stationary industrial motors which apply radial flux to their operation, it might be more productive to compare them to other lightweight axial flux units, such as those from Emrax or YASA.
Magnax shows, in its white paper, that their motors can be as small as 150 millimeters (5.9 inches) in diameter to over 5,400 mm (212.6 inches). The larger sizes would be destined for industrial or wind turbine applications.
Emrax motors range from 188 mm to 348 mm, all designed for power applications on lightweight devices. The 188 mm unit produces 70 kilowatts (93.8 pounds) from 6.8 kg. (14.96 pounds), while the 348 mm motor can put out 300 kW (402 hp.) from its 40 kilogram (88 pound) mass. Peak torques for the larger motor is a massive 1,000 Newton-meters (737 foot-pounds). The 188 produces 6.27 hp. per pound: the 348 makes about 4.6 hp. per pound.
Magnax’s white paper makes a direct comparison between YASA’s P400S and their AXF275. The 305 mm. diameter P400S weighs 27 kilograms (59.4 pounds), while the AXF275 (mm. diameter) weighs 24 kg. (52.8 pounds). The P400S puts out 160 kilowatts for a maximum power density of 5.92 kilowatts per kilogram. Magnax takes it up a notch, though, with its claimed 300 kilowatt maximum power for a power density of 12.5 kilowatts per kilogram.
The company hopes to have production motors available by the end of this year, with some introductions in October. With direct drive and significant power-to-weight ratios, Magnax’s intended markets in transportation and wind turbines seem like logical places to see this technology in action. Now, if we could see a similar improvement in batteries….