32 n MOTORS May 2025 www.drivesncontrols.com How to optimise the thermal performance of flat motors Flat brushless DC (BLDC) motors – so called because of their form factor – are used when small dimensions are essential, and the high performance typical of BLDC motors is required. This makes them ideal for applications such as robots, drones and medical devices. However, despite their advantages, their small surface area reduces heat dissipation, and requires additional considerations to improve thermal management. This is vital to optimise performance and eciency, and to ensure reliability and a long service life. The compact size and geometry of a at motor play a crucial role in its thermal performance. Extending their surface area to improve heat dissipation would compromise a major attraction. To improve the thermal management of the at design, materials need to be assessed. Metals with high thermal conductivity – such as copper and steel alloys, and aluminium – are ideal because they enhance heat dissipation, while materials with low thermal conductivity – such as plastic and rubber – act as insulators and can trap heat. Magnet quality also aects the heat generated by hysteresis losses, which occur when the magnetic core magnetises and demagnetises repeatedly, causing energy losses through heat due to material resistance. Samarium cobalt (SmCo) and aluminium nickel cobalt (Alnico) magnets oer improved thermal stability compared to neodymium (NdFeB) magnets, though super-high (SH) and ultra-high (UH) grade NdFeB magnets can be used for hightemperature requirements. Thinner laminations in the stator core might be needed to reduce eddy current losses. These circulating currents induced by changing magnetic elds cause resistive heating. If required, laminations made of nickel and cobalt alloys can enhance thermal stability compared to typical silicon iron materials. Winding design also has a signicant role, because increasing the number of turns adds to the length of the wire, raising its resistance, and causing further heat losses. Wire gauge and winding patterns also in uence heat generation and dissipation, while the wire insulation material aects heat management. Resin or epoxy coatings can be applied to the windings to withstand thermal shock and improve thermal integrity. Design elements may also be needed, such as ventilation slots to enhance thermal performance. This can improve heat transfer from core components, while heatsinks and conductive materials further help passive cooling. Active cooling methods – such as fans or forced air through tapered rotor slots – can also be integrated. In the compact footprint of a at motor, minimising heat-causing friction between moving parts is also vital. Understanding the demands that will be placed on the motor during operation is also key to optimising thermal management. Higher loads result in increased currents, leading to copper losses due to the resistance of the windings, so understanding the motor’s thermal limits under dierent load conditions is crucial. The duty cycle also aects the motor’s thermal behaviour. Motors in continuous operation or with high duty cycles will typically generate higher temperatures, requiring more robust cooling. Alternatively, applications that require dynamic control will generate high peak currents, also resulting in specic heat generation patterns. Speed aects heat generation due to increased windage and electrical losses. Highspeed operation can aect cooling eciency if the cooling mechanisms are not adequate, although for outer-rotor motors, higher speeds also help with natural air convection and heat dissipation. The environment in which a at motor operates is another crucial consideration. Higher ambient temperatures make it more dicult for the motor to cool down, increasing the dependency on design, as well as material and lubricant selection. This issue is compounded when heat radiation sources are present, and in such cases, eective heat shielding is required. Humidity can also impact thermal performance by causing insulation breakdown and electrical short circuits. Moisture build-up can disrupt heat dissipation, reduce eciency and cause corrosion, so adequate sealing and moisture protection are crucial to maintaining reliable operation. While materials and design features are crucial, sub-assembly and motor assembly processes also aect thermal performance. Precision tools and manufacturing processes are needed to ensure that motor assembly achieves precise tolerances. In high-performance applications involving BLDC at motors, thermal management is a vital consideration. With appropriate specication, BLDC at motors can be reliable and durable. n The small size of brushless DC at motors means that careful thermal management is required. Portescap design engineer, Vishal Sapale, explains the process of motor selection for e ective thermal management. In high-performance applications involving BLDC at motors, thermal management is vital.
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