Analysis of Silicon Steel Sheets in Brushless Motors

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The rotor of a brushless motor consists of two parts: an internally composed rotor core made of silicon steel sheets and a surface-mounted permanent magnet. This is the surface-mounted permanent magnet structure.

Why does a brushless motor need silicon steel sheets?

Isn’t it said that a current-carrying conductor can produce an effect in a magnetic field? Then why do we need silicon steel sheets? Air has weak magnetic conductivity, but iron is magnetic conductive. The role of silicon steel sheets is to guide the magnetic path of the magnet and form a loop, requiring the magnetic reluctance (think of it as resistance) of the brushless motor to be relatively small. However, you may wonder why both the stator and rotor are made up of laminated sheets?

Do you know the principle of an induction cooker?

Why does an iron pot placed on an induction cooker heat up? This is because materials similar to iron placed in a rapidly changing electromagnetic field (think of alternating current; that electricity is flying back and forth momentarily, unlike direct current that always goes from positive to negative) will generate eddy current losses and heat up, with the heating effect increasing with higher frequencies. Silicon steel sheets placed in the rotating magnetic field of the motor encounter the same issue, and the solution is to add silicon to the steel and create thin sheets. Theoretically, the thinner the silicon steel sheet, the smaller the eddy current losses.

So, do you now understand why conventional fixed-wing motors mostly use thicker 0.35mm silicon steel sheets, while helicopter and ducted fan motors mainly use 0.2mm silicon steel sheets? The faster the motor speed, the faster the magnetic field changes, resulting in larger eddy current losses. Nowadays, most brushless motors use 0.2mm single-piece silicon steel sheets, reducing iron losses in the motor.

This concludes the analysis of silicon steel sheets in brushless motors. We hope this information is helpful to users. Faradyi Motors Co., Ltd specializes in the research and development of brushless motors, DC brushless motors, brushless drivers, and other motion control products, providing professional technical support and customized solution development.