Brushless DC Motors Sohaib Hasan

Motor Basics What is a motor –Converts electrical energy into kinetic energy Where did it come from –Identification of rotating magnetic field principle by Nicola Tesla in 1882 –Introduction of Electric Motor by Nicola Tesla in December 1889 (U.S. Patent )

Parts of a Motor 1.End Bell Fastners 2.Shaft Key & Keyways 3.Bearing & Brushings 4.End Ball Flanges 5.Identification Plates 6.Wire Warnish 7.Commutators 8.Brush Holders 9.Laminations 10.Conduit Connection Box 11.Magnets (Ferrites) Brushless Motor Components Brush Type Motor Components Images courtesy of Hernon Adhesives & Sealents (

Parts of a Motor Images courtesy of How Stuff Works (

How It Works When electric current passes through a coil in a magnetic field, the magnetic force produces a torque which turns the motor. Force in Motor: F=ILB F = Force B = Magnetic Field L = Length of Conductor I = Current in Conductor Torque in Motor: T = IBA sin θ A = LW L = Length of Winding W = Width of Winding Images courtesy of Wikipedia (

Motor Types

Brushless DC Motor No Commutators Position of Coils with respect to the magnetic field is sensed electronically. Current is commutated through electronic switches to appropriate phases.

How it Works Halls Sensors sense the position of the coils The Decoder Circuit turns appropriate switches on and off The voltage through the specific coils turns the motor Images courtesy of Servo Magnetics (

Advantages Increased Reliablilty & Efficiency Longer Life Elimination of Sparks from Commutator Reduced Friction Faster Rate of Voltage & Current Precision Voltage & Current Applied to Field Coils

Applications Low Power –Consumer Electronics –Medical Field High Power –Industrial Machinery –Vehicles –Airplanes

Disadvantages Requires Complex Drive Circuitry Requires additional Sensors Higher Cost Some designs require manual labor (Hand wound Stator Coils)

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