Researchers at Germany’s esteemed Fraunhofer research organization have developed a casting technique to produce lightweight aluminum windings with a higher groove fill factor than conventional copper wire.
The coils are composed of cast aluminum, and are based on a flat conductor arrangement, which leads to a higher slot fill factor and thus better use of the available installation space. Although the cast aluminum coils have a higher electrical resistance relative to the wound copper coils, the larger cross-section results in less resistance with respect to the entire coil.
Fraunhofer says the aluminum’s better connection to the laminated core and more efficient use of installation space results in much better thermal and electromagnetic behavior. To that end, manufacturers could replace copper wires with cast aluminum and enjoy improved performance and lower material costs.
Researchers tested the new technology on commercially-available e-bikes, and found that the aluminum coils increased the groove fill factor from 32% to 60% and led to a 10% weight savings. Torque increased by 30% and continuous power at operating temperature increased by almost 20%. Aluminum coils deliver heat more efficiently to the laminated core, which results in improved continuous performance, since the coils only reach the continuous operating temperature at higher currents.