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A historical pioneer in the complex technology of electric motors without magnets Those who know the history of electric machines will find the title and verbi

A historical pioneer in the complex technology of electric motors without magnets Those who know the history of electric machines will find the title and verbiage very amusing. Motors with no permanent magnets were the first practical ones, and at this point wound-rotor motors are over a century old. It's worth noting that some of the biggest motors have always been designed this way, because the size of magnets required would make them both too expensive and dangerous, and still not powerful enough for their size; a field coil can generate a field that's only limited by the current and resistive heating of the winding, but rare earth magnets have fixed limits on field strength.

XorNot 4mo ago
Not quite true: you're also limited by the mechanical strength of your windings and core (this is the upper limit on superconducting magnets like at CERN and in fusion plants).
- Jblx2 4mo ago
  And if you also ignore iron saturation.
butWhathuh 4mo ago
[flagged]
- deleted 4mo ago
  [deleted]
xeonmc 4mo ago
What advantage do permanent magnets provide that it isn't the case that all motors are made without them?
- sitharus 4mo ago
  A lack of wear components. A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement. Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field. This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency. You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
  - Rapzid 4mo ago
    To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
    - handstitched 4mo ago
      It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
      - namibj 4mo ago
        The actual alternative is induction motors, which are just a bit less efficient than PMSM and otherwise basically the same. Except that the frequency fed to them isn't exactly proportional to speed. They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
      - mcdonje 4mo ago
        Another comment said they're not using brushes, so they shouldn't need more maintenance.
    - _kulang 4mo ago
WalterBright 4mo ago
Long ago, when I was in Cub Scouts, one of the projects was to build an electric motor. The parts list was: 1. a plank to form the base 2. several 6 inch nails 3. wire 4. a tin can (as a source of sheet metal) 5. tape No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in. A loud vibration ensued, and then it burst into flames. My mom wasn't happy.
- WalterBright 4mo ago
  P.S. I still use tin cans as a source of sheet metal. There was a big storm a while ago, with tree branches whistling by at high speed. (Not a good time to be outside.) Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing. I've used coke can metal for shingles and flashing, too. They don't rust.
  - fragmede 4mo ago
    there's also a plastic liner on them that I'm sure helps.
    - echoangle 4mo ago
      It also helps that they are made from aluminum which doesn’t rust like iron does.
      - euroderf 4mo ago
        And epoxy binds to aluminum just fine ? Epoxy is weird. What solid material does it NOT bond to ?
        ridgeguy 4mo ago
        Teflon.
anonymousiam 4mo ago
You're right about the verbiage being amusing. All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient. In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.
- rdtsc 4mo ago
  > field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient That and not having huge strong magnets is nice when doing maintenance.
hackrmn 4mo ago
Verbiage? What about the _nounage_?

XorNot 4mo ago

Not quite true: you're also limited by the mechanical strength of your windings and core (this is the upper limit on superconducting magnets like at CERN and in fusion plants).

Jblx2 4mo ago
And if you also ignore iron saturation.

butWhathuh 4mo ago

[flagged]

deleted 4mo ago
[deleted]

xeonmc 4mo ago

What advantage do permanent magnets provide that it isn't the case that all motors are made without them?

sitharus 4mo ago
A lack of wear components. A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement. Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field. This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency. You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
- Rapzid 4mo ago
  To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
  - handstitched 4mo ago
    It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
    - namibj 4mo ago
      The actual alternative is induction motors, which are just a bit less efficient than PMSM and otherwise basically the same. Except that the frequency fed to them isn't exactly proportional to speed. They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
    - mcdonje 4mo ago
      Another comment said they're not using brushes, so they shouldn't need more maintenance.
  - _kulang 4mo ago

WalterBright 4mo ago

Long ago, when I was in Cub Scouts, one of the projects was to build an electric motor. The parts list was: 1. a plank to form the base 2. several 6 inch nails 3. wire 4. a tin can (as a source of sheet metal) 5. tape No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in. A loud vibration ensued, and then it burst into flames. My mom wasn't happy.

WalterBright 4mo ago
P.S. I still use tin cans as a source of sheet metal. There was a big storm a while ago, with tree branches whistling by at high speed. (Not a good time to be outside.) Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing. I've used coke can metal for shingles and flashing, too. They don't rust.
- fragmede 4mo ago
  there's also a plastic liner on them that I'm sure helps.
  - echoangle 4mo ago
    It also helps that they are made from aluminum which doesn’t rust like iron does.
    - euroderf 4mo ago
      And epoxy binds to aluminum just fine ? Epoxy is weird. What solid material does it NOT bond to ?
      - ridgeguy 4mo ago
        Teflon.

anonymousiam 4mo ago

You're right about the verbiage being amusing. All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient. In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.

rdtsc 4mo ago
> field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient That and not having huge strong magnets is nice when doing maintenance.

hackrmn 4mo ago

Verbiage? What about the _nounage_?