Here's a nice discussion about Switched Reluctance Motors courtesy of TI (and control thereof):
http://www.ti.com/lit/an/spra420a/spra420a.pdf
An electric motor that does not need expensive rare-earth magnets
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Re: An electric motor that does not need expensive rare-earth magnets
#12The AC induction motor used in the Tesla doesn't use permanent magnets, so no rare earth metals either.
Re: An electric motor that does not need expensive rare-earth magnets
#13'rare-earth' does not mean 'rare' Wikipedia: > Although it belongs to the rare earth metals, neodymium is not rare at all.
It's also "not profitable" enough for corporation to mine in the USA.
But I believe Canadian corporations own the largest deposits in the USA?
Re: An electric motor that does not need expensive rare-earth magnets
#14Induction motors have long been in existence and they achieve the same goals too. In fact, many popular automotive companies still use Induction motors in their cars (Eg.Tesla). What makes these switch reluctance motors attractive over the induction motors , then? Could someone please clarify?? Thanks.
Full rated torque at 0 rpm.
Re: An electric motor that does not need expensive rare-earth magnets
#15Induction motors have long been in existence and they achieve the same goals too. In fact, many popular automotive companies still use Induction motors in their cars (Eg.Tesla). What makes these switch reluctance motors attractive over the induction motors , then? Could someone please clarify?? Thanks.
Induction motors are good for some things, bad for others
It has all to do with speed x torque (x power) behaviour, and how it's controlled.
To change the speed on an induction motor is complicated, as opposed to changing the speed in a DC motor, where you just change voltage supplied
Re: An electric motor that does not need expensive rare-earth magnets
#16"to deliver a given amount of twisting force—or torque—a reluctance motor has to be larger than an equivalent permanent-magnet motor"
Anyone know how much larger a reluctance motor would need to be? Seems like this would be a problem, since bigger usually means heavier, especially given that the motors are made of iron.
Re: An electric motor that does not need expensive rare-earth magnets
#17I went to the trouble of learning this just now, so I might as well share:
The most basic electric motor is to have two electromagnets which can rotate with respect to each other. You can make one fixed, but the other has to rotate while still being powered. This requires an electrical connection for a spinning part, and the easiest way was "brushes", apparently. These are literally just metal wires with some spring to them so they can maintain some contact with a rotating part. As you can imagine, this leads to frictional losses and wear, so low reliability.
Another option is to replace the spinning electromagnet with a spinning permanent magnet. That way you don't need the electrical connection, but you do need expensive rare-earth metals to form the permanent magnet.
Re: An electric motor that does not need expensive rare-earth magnets
#18'rare-earth' does not mean 'rare' Wikipedia: > Although it belongs to the rare earth metals, neodymium is not rare at all.
This is very true. If you are interested in learning about Nd magnets, have a read of my May 2012 article for Front of House(FOH) a professional audio trade magazine. Its on page 32 of the following link:
http://digitaleditiononline.com/publication/?i=110979
Apologies for not being able to provide a direct link, it is one of those "virtual issue" magazine sites.
Neodymium-based magnets are very important for the solenoid motor structures used in many types of loudspeakers.
Re: An electric motor that does not need expensive rare-earth magnets
#19I went to the trouble of learning this just now, so I might as well share: The most basic electric motor is to have two electromagnets which can rotate with respect to each other. You can make one fixed, but the other has to rotate while still being powered . This requires an electrical connection for a spinning part, and the easiest way was "brushes", apparently. These are literally just metal wires with some spring…
And then there is the option mentioned in the article, where the spinning permanent magnet is not made of expensive rare-earth metals, but rather of a metal in which a magnetic field is induced by stationary windings.
Re: An electric motor that does not need expensive rare-earth magnets
#20Squirrel Cage Induction Motors have been around for years and have been used in Industry forever.
No brushes, no magnets...