What actually is saturation? Is it like a hysteresis effect where the stator isn’t able to magnetize/demagnetize fast enough so it can’t effectively increase torque output?
You lost me at
All I know is there’s a point where the slope of the torque vs amps relationship starts to approach 0
There is a point over which efficiency tanks. Nothing would prevent you from exceeding it, as long as nothing was too hot.
A magnetic field is generated by drawing a current through a conductor. For any given coil(like one in a motor), once you reach a certain amp the field generated by this current can’t grow any stronger(atleast not in significant amounts). This is when it saturates. Its like pouring water into an already full cup. Like some already mentioned, this correlate to the torque as well.
This is also part why you usually hear that more copper equals stronger/better motor. Which is true for two equal motors with different amounts of copper.
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I’ll add to this being an EE as well, that the stator structure (how much cross-sectional area there is for the magnetic fields to form through) affects the maximum magnetizing force (ampere-turns).
“The magnetising force is provided by passing current through a wire or similar. The unit has the value amp-turns per metre , in the sense that the magnetising force is amplified by the number of turns of a coil of wire.”
This means that assuming that the amount of copper is the same, then you can have the same magnetizing force at different currents based on the turns wrapped around the stator teeth.
Had to learn and understand this concept as I was practising designing custom inductors/transformers and was looking at different core sizes, shapes and materials to use based on the wanted inductance and saturation currents.
There is also back-iron saturation in motors, which means that the amount of iron behind the magnets in an outrunner’s rotor for example is not thick enough to contain the magnetic field lines and they break out, which also lowers the inductance without increasing the generated torque. Although I don’t know if the 63xx motors are anywhere near those limits.
Now I suspect that the max currents that motors often specify is the reasonable limit where the saturation has caused like a 30% decrease in the inductance, but this should be tested and verified in a motor dyno with a standstill test with a lever arm against a scale and see how the motor’s torque is affected by the current and graph it out.
Here’s an example of a inductance/current graph from a pretty beefy inductor and you can see that the inductance is fairly stable until a certain current amount is reached and then it falls of very sharply. This behavior is also affected greatly by the material choice/mix of the core material. (https://www.digikey.fi/en/products/detail/würth-elektronik/7443642200/4865753)
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I tried to not complicate it too much, mentioning inductance is fair tho.
While I agree with the amp-turns explaination. I wonder how it applies to EDF motors that physically berly has one turn(basically just a short) but still seem to be total powerhouses.
Vedder plays around abit with it here; https://youtu.be/fbK2dcoYS7g?si=ta3QMAP7nvlKq5Zi&t=284
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The saturation point is solely determined by the core material. Regardless of how many amp-turns are around it the core has a maximum field strength it can hold before saturating and with electrical steel it’s like 1.7 Tesla and you can push it to maybe 2 Tesla maximum while saturating. If it’s maybe 3 amp turns and 100 amps or 10 amp turns and 30 amps the field strength limit will still be the same based on the core material. You can add more core for more surface area and torque but the field strength limit of the material is the same
If u have a coreless motor you can make a much stronger magnetic field with less heat as the core (electrical steel for us) isn’t saturating and MRI and superconductors don’t have a core …but need extreme cooling.
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Interesting. why does that happen?
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I think the field strength can infinitely increase (?) as you add current and heat is the only limitation when talking about just a coil (inductor) but the field strength is hard to build with just a coil. Adding a core in the coil can hugely increase the magnetic field strength but only up to the point of the core material’s ability to generate or hold that field.
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Physics
Looking at the equation, B → infinity when I does. But in order for that to happen you need a super conductor… and endless amounts of amps. (calculation is for a straight wire, slightly different for a coil where turns amplifies)
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Yes I’m aware of that equation. But my understanding is that saturation is essentially where this relationship starts to break down right? Are you saying that the material properties of copper change in some way as heat increases which hampers its ability to increase field strength ?
I only ask because my understanding was that saturation was related to the actual current level as opposed to thermal conditions. I thought it was essentially what governs maximum torque even over instantaneous timescales where thermal effects do not apply.
There’s no saturation with copper and just ferromagnetic or ferrimagnetic materials
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Huh When is there saturation?
Wow dudes, you guys know your shit i gotta tell ya 
You’ve lost the OP here i think though … 
And myself too i must add 
When u have a ferromagnetic core. IT saturates.
It’s not complicated folks. If ur confused read it again and then bam 
you know it
@b264 dont know what ur sad about.
They could be using some specific stator/core material blend with lower permeability, which gives in inductors a lower inductance for given turns, but a higher saturation current. Usually the cores (assuming same geometry, but different core material) with high inductance factor (less turns of wire for given inductance), would saturate at a lower current than a low inductance factor core with higher turn count of wire. Of course the high inductance factor core would likely be underwound, aka wasted space for more copper.
smaller EDF disassembly video, revealing a normal outrunner in it’s guts, looks like multiple turns of wire:
The EDF motor vedder had in the video is this (couldn’t find any info on number of turns used or pole count, but they’re outrunners), so I don’t think there is any special per say going on in the motor, but it is a specialized and expensive piece of kit, so I wouldn’t be that suprised if it has some more specific material choices being used:
He said he took it apart and inside was only what could be desribed has berly half a loop of a bussbar 
he said and I quote: “I have no idea why this spins, seems impossible, but it does”
Only core materials I’ve ever heard of being worthwhile for a motor of any type are electrical steel (iron) and maybe with a bit of cobalt