4 ms·

Brushes and slip rings seem like they would be more efficient, but they are adding friction and sparking that isn’t part of this, and as they wear become less e

Brushes and slip rings seem like they would be more efficient, but they are adding friction and sparking that isn’t part of this, and as they wear become less efficient. BLDC showed that induction wins through one conversion, but this is making 2. Simple napkin math: If you compare BLDC to Brushed efficiency. Best BLDC is 90% efficiency and best brushed is 80%. Even if the inductive rotor loses as much energy as the complete BLDC motor, it would still perform on par with a brushed motor.

TaylorAlexander 3y ago
Well, BLDC doesn’t really use induction at all. It just makes a magnetic field that pushes on magnets.
- deleted 3y ago
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- TaylorAlexander 3y ago
  I don’t understand why this is being downvoted? Is this a terminology thing? I design my own brushless motor controllers. A brushless motor operates by generating a magnetic field in fixed coils and using that magnetic field to directly act on magnets. Wikipedia defines magnetic induction thusly: “Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field.” So basically using a changing magnetic field to create voltage in a conductor. While it is true that induction occurs in a brushless motor as a secondary effect (the rotating rotor induces back EMF on the stator coils), the primary mechanism of movement is a magnetic field physically acting on permanent magnets - no induction involved. This is distinct from an AC induction motor, about which Wikipedia says: “An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.” Basically in an induction motor, induction is a required effect for the operation of the motor, rather than a side effect as in a brushless motor. So while induction occurs in a brushless motor, if induction could be magically disabled the motor would still work. This is not true for an induction motor.
  - effie 3y ago
    Indeed, BLDC doesn't use EM induction to excite the rotor, instead it uses directly macroscopic magnetic force due to current in stator acting on the permanent magnets in the rotor. The EM induction is present in the winding of the stator, and to some extent has to be present, to keep the current there low enough, otherwise we would get locked stator situation, and the winding would burn out.
    - TaylorAlexander 3y ago
      That’s true, each individual coil is an inductor, and without that inductance you would need a more complex drive circuit.

TaylorAlexander 3y ago

Well, BLDC doesn’t really use induction at all. It just makes a magnetic field that pushes on magnets.

deleted 3y ago
[deleted]
TaylorAlexander 3y ago
I don’t understand why this is being downvoted? Is this a terminology thing? I design my own brushless motor controllers. A brushless motor operates by generating a magnetic field in fixed coils and using that magnetic field to directly act on magnets. Wikipedia defines magnetic induction thusly: “Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field.” So basically using a changing magnetic field to create voltage in a conductor. While it is true that induction occurs in a brushless motor as a secondary effect (the rotating rotor induces back EMF on the stator coils), the primary mechanism of movement is a magnetic field physically acting on permanent magnets - no induction involved. This is distinct from an AC induction motor, about which Wikipedia says: “An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.” Basically in an induction motor, induction is a required effect for the operation of the motor, rather than a side effect as in a brushless motor. So while induction occurs in a brushless motor, if induction could be magically disabled the motor would still work. This is not true for an induction motor.
- effie 3y ago
  Indeed, BLDC doesn't use EM induction to excite the rotor, instead it uses directly macroscopic magnetic force due to current in stator acting on the permanent magnets in the rotor. The EM induction is present in the winding of the stator, and to some extent has to be present, to keep the current there low enough, otherwise we would get locked stator situation, and the winding would burn out.
  - TaylorAlexander 3y ago
    That’s true, each individual coil is an inductor, and without that inductance you would need a more complex drive circuit.