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| Switched reluctance motors will save the planet? |
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| EEVblog:
--- Quote from: wraper on July 27, 2020, 11:13:48 pm ---They are also used in microwave oven fans BTW. --- End quote --- Microwave oven fans would be the epitome of the cases where it doesn't matter. i.e. you have an already high load (1000W) working for only a few minutes a day. |
| james_s:
Shaded pole motors are used everywhere, bathroom vent fans, desk fans, AC powered muffin fans, furnace and boiler draft inducers, medium sized fountain pumps, anywhere that requires a cheap low power AC motor. There are other types of induction motor such as PSC or even 3 phase motors that can easily be scaled down into these sizes, they just typically aren't because it costs so much more. My ~15 year old Maytag Neptune washing machine has a switched reluctance motor. It works fine although these days it seems like VFDs are cheap and good enough that ordinary 3 phase induction or BLCD motors probably make more sense. If they banned shaded pole motors I suspect PSC and BLCD would take over most applications where they are now used. |
| filssavi:
Now I didn’t watch the video, but I can assure switched reluctance machines are absolutely a thing, the operating principle is the same as the BLDCs however instead of magnet the rotor is has a highly asymmetric radial reluctance profile. You also have synchronous reluctance (synrel) machines that work more like PMSMs but use the same principle. There are even hybrid machines where some torque is due to magnets and some torque is due to reluctance. Performance wise they are (for most Typical applications) strictly worse than permanent magnets machines, and typically(though not necessarily) have a terrible power factor (0.5-0.7 lagging) however they cost much less and you don’t rely on a single country for rare earths magnets. They are still better than induction machines though as there are no rotor copper losses That said these type of machines are extremely rugged, as the rotor is basically a hunk of solid steel, they don’t have brushes, rotor bars that can break, magnets that demagnetise etc just stamped steel laminations bonded together. |
| Jay_Diddy_B:
Hi, Switched reluctance motors have been around a long time, at least 40 years. The Dyson digital motor used the Dyson vacuum cleaners and hand driers are switched reluctance motors. They are very similar to stepper motors. They tend to by noisy and have pulsating torque, the rotor tends to 'snap' from one position to another. There is a Goodness Factor for electric motors: More here: https://en.wikipedia.org/wiki/Goodness_factor#:~:text=The%20goodness%20factor%20is%20a,efficient%20magnetic%20levitation%20induction%20motors.&text=From%20this%20he%20showed%20that,likely%20to%20be%20relatively%20large. This helps explain why switched reluctance motors are good. Ae is relatively large, short windings of thick wire. Le is the length of the electrical circuit, it can be short. W is large high RPM They also need a driver. This goodness factor explains why large machines are better, more efficient than small ones. If you scale the linear dimensions, the areas, Ae and Am scale with the linear dimensions squared, Le and Lm increase proportional to the linear dimension. So goodness gets better. It also explains why switch mode power supply transformers are better than line frequency ones for a given size. The idea that the switch reluctance motor will save the planet seems like a lot of hype to me. Jay_Diddy_B |
| filssavi:
--- Quote from: james_s on July 28, 2020, 04:02:30 am ---My ~15 year old Maytag Neptune washing machine has a switched reluctance motor. It works fine although these days it seems like VFDs are cheap and good enough that ordinary 3 phase induction or BLCD motors probably make more sense. If they banned shaded pole motors I suspect PSC and BLCD would take over most applications where they are now used. --- End quote --- Switched reluctance machines require a VFD just as much as a BLDC, the main reason they are not used in white goods and general consumer crap is not the drive requirements, but just the higher cost, that is not justified by any real advantage. Powe density is fine and good, however there is plenty of space inside the whashing machine. Efficiency wise the difference, at the low power levels we talk about is negligible (you will have maybe few watts difference if that) |
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