[userbinator]

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.

[WalterBright]

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]

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.

[psd1]

I like that story. I fixed a microwave door latch with a beer-can shim and some decorative ribbon; we used it another 11 years.

[fragmede]

there's also a plastic liner on them that I'm sure helps.

[echoangle]

It also helps that they are made from aluminum which doesn’t rust like iron does.

[hdrz]

It rusts just like iron, but the rust (AlOx, or alumina) stays bonded to the metal and actually protects it.

[lloeki]

Rust being literal Fe2O3 makes a convincing argument that aluminium sure oxidises but doesn't rust pretty much by definition ;)

[wongarsu]

In other words: it rusts, but it doesn't rust like iron. It rusts in a much less destructive way because the aluminum oxide protects the rest of the aluminum from oxygen

[euroderf]

And epoxy binds to aluminum just fine ? Epoxy is weird. What solid material does it NOT bond to ?

[AlotOfReading]

Polyethylene, like they use in food containers. Virtually nothing sticks to it unless specifically designed.

[mjanx123]

It does not bond to polypropylene and other low surface energy plastics

[ridgeguy]

Teflon.

[toss1]

One of my favorite sayings:

"Good judgement comes from experience; experience comes from bad judgement."

I commend your excellent use of bad judgement there, WalterBright (despite your mom's lack of enthusiasm)!

[rbanffy]

That 60Hz sound is a sure sign we did something very wrong. By the time you hear it it’s usually too late to say “Uh oh”

[actinium226]

Username checks out.

[Daub]

Been there. Im gonna guess that 90% of HN folk have similar stories to tell.

[WalterBright]

The Cub Scouts in the 1960s were a lot of fun. Each den meeting involved a project. The other one I remember was we each built a kite from scratch.

Mine was a bit fragile, and the first gust of wind shredded the sticks and plastic film.

But it was still fun!

As a teen I built a flame thrower. No, I'm not going to explain how to build one. My dad told me that God looks out for little boys, because otherwise they'd never survive to adulthood.

When I was 9, I found a book of his "Rocket Manual for Amateurs". The opening sentence was something like "if you're fascinated by things that burn and explode, this book is not for you." Who could resist a teaser like that? I promptly read it cover to cover. He wouldn't let me buy any of the necessary materials.

[ridgeguy]

"Rocket Manual for Amateurs" was my favorite book after I found it in 8th grade. In high school I had a chem teacher who would give me chemicals so I could experiment with what I'd read. A great book for budding Raketenkinder.

[Daub]

> if you're fascinated by things that burn and explode, this book is not for you.

Translation… ‘read me now!’

[anonymousiam]

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]

> 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.

[XorNot]

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]

And if you also ignore iron saturation.

[xeonmc]

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

[sitharus]

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.

[snovv_crash]

You can also make squirrel-cage rotors that are auto-inductive in the sense that they resist slip from the rotating field of the stator. This is also extremely simple to manufacture and doesn't require driving separate fields or anything similar.

[adrian_b]

This is mentioned in the parent page, where it is also mentioned that their disadvantage is a lower energy efficiency than either electrically-excited synchronous motors or permanent-magnet motors.

The lower efficiency means a lower range for the same battery, which is why the companies that have used them in the past, like Tesla, have abandoned them.

Permanent-magnet motors have the highest possible energy efficiency, followed by electrically-excited synchronous motors, than by the induction motors mentioned by you.

Both permanent-magnet motors and induction motors do not contain parts that need frequent maintenance, while this property is more difficult to achieve for electrically-excited synchronous motors.

[hulitu]

> The lower efficiency means a lower range for the same battery,

And some heat which must be dissipated or else they will dethrone the BMW as the leading burning car. /s

[ipbrown]

I am a little surprised that Renault is only claiming a drive cycle efficiency of 92% (unclear for which drive cycle). It is possible to design EESM with brushless high frequency rotating transformers and rectifiers for WLPT drive cycles with greater than 94% almost 95% efficiency.

[Rapzid]

To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.

[_kulang]

It’s a near-doubling of energy loss - probably a healthier way to understand it when the efficiencies are all 90%+

[Maxion]

Funnily enough if enough of that energy loss (heat) can be scavange, this wouldn't be nearly that bad for us living up here in the cold.

[antonkochubey]

In most EVs motors are watercooled, so that energy can indeed be scavenged – problem is, during low-speed driving, the heat output is not high enough to get noticeably above ambient temperature.

[_kulang]

Thermodynamically, heat is waste energy. EVs are so efficient that scavenging isn’t practical anymore; I’m not sure the temperature gets high enough to usefully extract the heat energy for heating. ICE cars obviously produce mostly heat so getting a radiator hot enough to heat the cabin is very easy

[tbrownaw]

You can get about 2/3 as much output power for a given amount of waste heat and cooling capacity.

It's like how laptop power bricks used to be big and get hot, and now they aren't and don't.

[handstitched]

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]

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]

Another comment said they're not using brushes, so they shouldn't need more maintenance.

[hackrmn]

Verbiage? What about the _nounage_?