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With windmills, strong magnets are useful because they reduce or eliminate the gearbox. PM motors can be efficient at lower speeds than induction motor so it s
by hwillis 9y ago
With windmills, strong magnets are useful because they reduce or eliminate the gearbox. PM motors can be efficient at lower speeds than induction motor so it simplifies and shrinks the nacelle, raises efficiency a bit, and might lower maintenance. That said, it's totally not necessary.
>electromagnetism/induction is somewhat more complex to manage but potentially more powerful and efficient.
Quibble- at certain RPM ranges an induction motor can be more efficient than a PM motor of equal cost, but in general a PM motor will always be smaller and more efficient than an induction motor if built to the same quality. For most applications, the cost of the motor is very minor.
Wind turbines are an exception because the converter is cheaper than the motor at that scale. Tesla uses induction motors for several reasons but the primary one is probably cost. The cost is actually more in materials handling and assembly than the magnets themselves, since magnets will always find a way to fuck up your life eventually. PM motors also have much more demanding requirements of controllers and more cogging, but in general they can only be as good as a PM motor at high speed and low load.
- strainer 9y agoInteresting but I am not sure you are not over generalising the legacy experience. With Tesla motors lately using induction motors for their top performance as well as their top economy models, that is a fair suggestion that 'PM free' can be superior, perhaps enabled by capabilities of modern power controllers.
- hwillis 9y agoTesla has very specific applications that make induction motors almost as good, but 3x cheaper. The efficiency of the motor is most important under that high-speed low-load point, when on the highway. PM motors have very large advantages over induction. They have half the iron laminations of an induction motor, so they have half the hysteresis losses. On an overall basis there is no way for an induction motor to make that up. Even at high RPMs I've only seen indications (papers/FEMM sims) that induction motors can roughly match PM motors, not surpass them.
- strainer 9y agoWhen I wrote the point of contention, i was thinking how it is possible to produce stronger magnetic fields electrically than ~materially, and what that should mean to ultimate motor performance. But I can see your correction is likely sound, that in practice PM options keep a performance edge -at least until the age of high temp superconductors arrive or other magic :)
- hwillis 9y agoSuch things exist: https://en.wikipedia.org/wiki/Superconducting_electric_machine https://en.wikipedia.org/wiki/Superconducting_electric_machi... A purely (doubly fed) superconductive motor would probably resemble a PM motor more than an inductive motor, but I'm not 100% sure. It would be for the same reduction in hysteresis losses. An air-core motor would also be possible, but that would result in 30 Tesla fields swinging around wildly, which would be a Bad thing. You could probably get good gains with metal glass laminations, if you were gonna make a hilariously expensive motor. It's got very low core loss and extremely high permeability, which lets you shrink the motor and have a higher ratio of copper/iron, lowering winding resistance. Still, electrical machines are so efficient it's kind of just not worth it. The friction in the bearings and the viscosity of air are significant factors in a motor's efficiency.