Ferrite as a stator material?

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Kodin   1 kW

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Ferrite as a stator material?

Post by Kodin » Jul 15 2016 3:07pm

Just curious, (and it's probably been asked before,) why is ferrite not used more often as a stator core material? For that matter, why not cast a composite out of epoxy or something that has the right ratio of iron and other materials required rather than cut super-thin laminate stacks and glue them together? I'd guess if there aren't commercial options out there one could make something with enough time and resources...
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Re: Ferrite as a stator material?

Post by amberwolf » Jul 16 2016 1:24am

Eddy currents.

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Re: Ferrite as a stator material?

Post by atarijedi » Jul 21 2016 3:07pm

Kodin wrote:Just curious, (and it's probably been asked before,) why is ferrite not used more often as a stator core material? For that matter, why not cast a composite out of epoxy or something that has the right ratio of iron and other materials required rather than cut super-thin laminate stacks and glue them together? I'd guess if there aren't commercial options out there one could make something with enough time and resources...
You could make one out of ferrite, just not as a single monolithic object. The field created by the rotor will induce eddy currents in the stator, this is what leads to heating in the stator. To counter this, you want to make your stator of magnetic but high resistance material. Currently, they do this by using steel laminations coated in an insulative material, so the generated eddy currents are confined individually to each lamination. Since these laminations are so thin, they are high resistance. The combination thinness, and isolating each lamination, minimizes eddy current losses.

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Re: Ferrite as a stator material?

Post by major » Jul 21 2016 5:05pm

Hi guys,

Ferrites are iron alloys made into ceramic. The material exhibits very low conductivity or in other words, very high resistivity. This minimizes eddy currents in the material. It is used a lot for high frequency applications for this very reason as transformer and inductor cores.

I believe there are actually quite a few motos using ferrite cores. Especially small ones where power density isn't an issue. Once tooled, it is an inexpensive part. One downside is the density and volumetric flux density meaning larger cores per output. Then the larger cores require longer coil turns. Some parts of motor cores have used ferrite or powdered metal (similar to ferrite, I think)*, such as pole shoes in automotive cranking motors.

major

*edit. Powdered metal is different from ferrite as it is conductive. It was/is used in DC where flux doesn't alternate.
Last edited by major on Jul 22 2016 8:26am, edited 1 time in total.

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Re: Ferrite as a stator material?

Post by amberwolf » Jul 22 2016 1:54am

Ah; then my post is wrong, and I misunderstood how it works. :oops:

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Re: Ferrite as a stator material?

Post by KD5ZXG » Nov 07 2018 10:26pm

I've molded a few composite inductor cores of JBWeld (5% Ferrosilicon "steel" Filler). Can highly recommended for energy storage or flyback choke only, not for motor. Too much reluctance from too much distributed gap. Only conducts flux 3~6x better than air, which might be enough to guide the field out of (and not setting up eddy currents in) your wire. Its certainly suitable for gluing up blocks of ferrite or other sintered powders. Or when you don't want flux to mushroom as it crosses an unfilled gap. Or don't want a gap to be mechanically unsupported. I just shave a sliver to 3x the calculated air gap and glue it in, problem solved.

Now you can fill JB much further than 5% (with crushed material) to carry more flux. But even solid ferrite only carries about 1/3 the flux of iron. Its going to make for a very weak motor, unless perhaps you build for high RPM instead of high torque. Epoxy will
block eddies bigger than any conductive iron particles suspended in it, so long as they aren't packed so tight they touch. Plenty of magnetic materials, like ferrite, are near electrical insulators anyway.

So, lets talk about ferrite for moment. What it is and isn't. Its a crushed and sintered artificial gemstone. Made of Iron Oxide and Zinc Oxide. The iron is always a hard magnet, hard as in permanent like the back of a loudspeaker. Takes a lot of energy (high remnance) to flip from one pole to the other. For soft forgetful magnets (low remnance) like flyback transformers: Manganese Oxide and/or Nickle Oxide are added. I don't have a clue what the Zinc does, maybe its mechanical...

Manganese isn't magnetic by itself, and nickle just barely is. But put them in crystal with iron and they seem to pick up a clue about how to act like iron does, except they forget more easily than iron. But you have to operate below the threshold where disordered iron begins to get involved, or it starts to organize into domains, and then its ruined. Becomes lossy ferrite like you might see for a suppressor bead. Disorder can only be restored by putting in an oven, regular "demagnetizing" won't restore the required small scale disorder to the iron, only create a balance of ordered domains which isn't the same. Manganese knows and cares the difference.

So anyways, I ruined my first composite core by doing everything wrong, not knowing any better. I smashed up a bunch of supressor type ferrite beads, which makes a bunch of dangerous sharp and insoluble powder you do NOT want to breathe. Then inverted a ziplock bag over my hand (holding a neodymium in my fingers) to mop up the powder. Flipped the bag closed and man, I was a genius! WRONG...

1st mistake: Supressor ferrite. 2nd mistake: striking ferrite, unshielded from Earth's field. 3rd Mistake: picking up with Neodymium. I could have fixed all that in a sufficiently hot oven, or maybe a microwave. But didn't know I needed to, until after was already molded into an Epoxy that now wouldn't survive the Curie temperature. Had to start over, but eventually wound a racetrack core in Litz, good to 1MHz.

Want to make a boost converter for your bike? Maybe epoxy with ferrite filler is good stuff. Motor you are wasting time unless you got a plan way outside the usual box. I got no clues but absolutely silly RPM how you might approach that.

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Re: Ferrite as a stator material?

Post by liveforphysics » Nov 08 2018 1:03pm

Brilliant post, thank you for sharing KD5ZXG!

KD5ZXG wrote:
Nov 07 2018 10:26pm
I've molded a few composite inductor cores of JBWeld (5% Ferrosilicon "steel" Filler). Can highly recommended for energy storage or flyback choke only, not for motor. Too much reluctance from too much distributed gap. Only conducts flux 3~6x better than air, which might be enough to guide the field out of (and not setting up eddy currents in) your wire. Its certainly suitable for gluing up blocks of ferrite or other sintered powders. Or when you don't want flux to mushroom as it crosses an unfilled gap. Or don't want a gap to be mechanically unsupported. I just shave a sliver to 3x the calculated air gap and glue it in, problem solved.

Now you can fill JB much further than 5% (with crushed material) to carry more flux. But even solid ferrite only carries about 1/3 the flux of iron. Its going to make for a very weak motor, unless perhaps you build for high RPM instead of high torque. Epoxy will
block eddies bigger than any conductive iron particles suspended in it, so long as they aren't packed so tight they touch. Plenty of magnetic materials, like ferrite, are near electrical insulators anyway.

So, lets talk about ferrite for moment. What it is and isn't. Its a crushed and sintered artificial gemstone. Made of Iron Oxide and Zinc Oxide. The iron is always a hard magnet, hard as in permanent like the back of a loudspeaker. Takes a lot of energy (high remnance) to flip from one pole to the other. For soft forgetful magnets (low remnance) like flyback transformers: Manganese Oxide and/or Nickle Oxide are added. I don't have a clue what the Zinc does, maybe its mechanical...

Manganese isn't magnetic by itself, and nickle just barely is. But put them in crystal with iron and they seem to pick up a clue about how to act like iron does, except they forget more easily than iron. But you have to operate below the threshold where disordered iron begins to get involved, or it starts to organize into domains, and then its ruined. Becomes lossy ferrite like you might see for a suppressor bead. Disorder can only be restored by putting in an oven, regular "demagnetizing" won't restore the required small scale disorder to the iron, only create a balance of ordered domains which isn't the same. Manganese knows and cares the difference.

So anyways, I ruined my first composite core by doing everything wrong, not knowing any better. I smashed up a bunch of supressor type ferrite beads, which makes a bunch of dangerous sharp and insoluble powder you do NOT want to breathe. Then inverted a ziplock bag over my hand (holding a neodymium in my fingers) to mop up the powder. Flipped the bag closed and man, I was a genius! WRONG...

1st mistake: Supressor ferrite. 2nd mistake: striking ferrite, unshielded from Earth's field. 3rd Mistake: picking up with Neodymium. I could have fixed all that in a sufficiently hot oven, or maybe a microwave. But didn't know I needed to, until after was already molded into an Epoxy that now wouldn't survive the Curie temperature. Had to start over, but eventually wound a racetrack core in Litz, good to 1MHz.

Want to make a boost converter for your bike? Maybe epoxy with ferrite filler is good stuff. Motor you are wasting time unless you got a plan way outside the usual box. I got no clues but absolutely silly RPM how you might approach that.
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Re: Ferrite as a stator material?

Post by KD5ZXG » Nov 14 2018 9:30pm

Then let me ask a few physics question that's been puzzling me.

Why does flux in free space mushroom around the easiest path instead of the entirety taking the easiest path? I'm assuming its like different resistors in parallel, but I'm not sure. Then you got quanta, which means lines instead of a smooth spread?

How does iron provide a shortcut through free space? Or why does flux not store the usual toll of energy to cross iron space?

Can't find any link that tells. All dumbed down to the point of lies, or mathed up to the point I can't even begin to understand. What gives here, flux tunnels across? Electron spins on opposite sides tangled? Wild guesses I just made up (file under lies), cause I really don't know...

Which brings me to electric charges. Is this the same as lines of flux, but punching through sideways from some additional dimension? Would kinda explain why equal positive and negative if the loop has to complete at another point somewhere nearby. Don't take as fact, I've probably got it all wrong.

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Re: Ferrite as a stator material?

Post by amberwolf » Nov 14 2018 10:22pm

KD5ZXG wrote:
Nov 14 2018 9:30pm

Why does flux in free space mushroom around the easiest path instead of the entirety taking the easiest path?
AFAIUI, in my extremely simple layman's view, it's because the lines push each other away.

When inside a concentrating material they can't do that as easily.

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Re: Ferrite as a stator material?

Post by fechter » Nov 14 2018 11:03pm

There's another material called Metglas that may have the best magnetic properties for a motor. Most ferrites will saturate at a much lower flux than steel. We want the highest possible saturation flux and at the same time, minimal eddy current and hysteresis losses. But Metglas would be hard to work with and it isn't cheap. It's mainly used for power line transformers where the reduced losses add up to a lot of money. Metglas might not be the ultimate in saturation flux either, but it would be a trade off for lower losses.
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Re: Ferrite as a stator material?

Post by Capo_au » Dec 18 2018 8:39pm

I know i'm a little late to the conversation but I might be able to shed a little light on the topic. As was mentioned above, ferrite only makes sense for high frequency applications where minimising core losses are your main concern. This is because of its low saturation magnetisation, which is typically less than 0.5 T for soft ferrites, will greatly limit the torque density of an electric motor compared to Fe-Si steel laminations.

Amorphous materials like those produced by Metglas have been investigated for use in electric motors.

The main benefits are:
  • The method of production (melt spinning) means they have an inherently low thickness of around 25 microns, which helps reduce corelosses
  • Their low coercivity of ~1 to 3 A/m helps minimise hysteresis losses.
  • A relatively high electrical resistivity when compared to Fe-Si steels, which helps minimise eddy current losses
The downsides are:
  • Amorphous materials are expensive to produce and expensive to stamp out due to their high hardness and high ductility
  • They typically have a very high saturation magnetostriction (shape change upon polarisation), making them noisy when used as an electric motor
  • Their saturation magnetisation at room temperature is only around 80% that of Fe-Si (3wt%) steel. It also falls off quickly as the temperature is raised
  • Their maximum service temperature is relatively low
  • Due to their low thickness the lamination stacking factor also tends to be quite low compared to Fe-Si steel lamination, further reducing a motors torque density.
I'm a materials engineer who develops soft magnetic materials for a living so feel free to pick my brain on the topic :thumb:

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Re: Ferrite as a stator material?

Post by spinningmagnets » Dec 18 2018 10:00pm

Ferrite is an element of the Lemco Agni motor, by Cedric Lynch. I don't understand it, though...

https://en.wikipedia.org/wiki/Lynch_motor

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Re: Ferrite as a stator material?

Post by fechter » Dec 19 2018 12:18am

Capo_au wrote:
Dec 18 2018 8:39pm
I'm a materials engineer who develops soft magnetic materials for a living so feel free to pick my brain on the topic :thumb:
Thanks. Magnetism is still sort of a black art.

I didn't consider the magnetostriction of Metglas. It might be good as an ultrasonic driver then.

Can you think of a better material for motor cores? Most seem to use silicon steel but if there was a more expensive but better performing material, we might want to use it.
"One test is worth a thousand opinions"

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Re: Ferrite as a stator material?

Post by Capo_au » Dec 19 2018 12:51am

Thanks for the link, that's an interesting read.

I may be wrong, but from the looks of it a Lynch motor is just a brushed axial flux motor with solid conductors for the armature and possibly more than three phases. While the wiki page does mention that earlier motors used ferrite cores it also says that they have since moved on to grain oriented (GO) Fe-Si steel. This is probably because the ferrite cored motors would have had a very poor torque density even if they did have a good efficiency. Their GO Fe-Si steel motors possibly have a better torque density and a good efficiency since GO Fe-Si steel has a coercivity about ~15% that of non-oriented Fe-Si steel. Magnax is another company that uses GO Fe-Si steel for this reason. Even then, the 1 kW/kg power to weight ratio for a Lynch motor is a fair bit lower than the numbers claimed by Emrax (dubious as those numbers are :shock: ) at 10 kW/kg.

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Re: Ferrite as a stator material?

Post by Archer321 » Jan 20 2019 12:08am

Ok, but if torque density is ignored for a moment, does a ferrite stator make for a more efficient motor?
Even if the motor has to be made physically larger to achieve the desired output.

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Re: Ferrite as a stator material?

Post by fechter » Jan 20 2019 12:45am

I would think so. Less loss = more efficient. Go one step further and use an ironless motor.
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Re: Ferrite as a stator material?

Post by spinningmagnets » Jan 20 2019 1:13am

Cedric Lynch could have used a motor style with very thin laminations, but I was under the impression that he was seeking very high efficiency in a specific size of motor package. His aero semi-recumbent E-motorcycle was his vision of a light and cheap single-rider vehicle to reduce the use of 4,000-lb four-seat cars burning gasoline.

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Re: Ferrite as a stator material?

Post by Archer321 » Jan 20 2019 1:28am

fechter wrote:
Jan 20 2019 12:45am
I would think so. Less loss = more efficient. Go one step further and use an ironless motor.
Interesting thought...but my understanding is that ironless motors are less efficient although I'm not sure why. Perhaps the benefit of having the "iron" in the stator to augment and channel the flux of the windings is greater than the losses due to eddy currents.
Which leads us back to ferrite with it's poor electrical conductivity and subsequent less eddy current losses.

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Re: Ferrite as a stator material?

Post by Jaan » Jun 08 2019 12:00am

Really interested topic and I hope once a day you people will successfully design a low losses, high efficiency, low premibility with high torque motor, because the technology is endless...
Just like ceiling fan example conventional fans takes 70-80W the ferrite Fans with BLDC will be 5-15W, let's who will be won to discover the same (waiting for next who will be the thomas Edison, Nicolas Tesla, Albert Einstein...
As per my poor knowledge the
a) ferrite is a miniature iron + other magnetics alloy + epoxy...
The ferrite's material is the most important part to provide a good flux with low losses,
b) In steel lamination stators, the peoples are using with thinest iron/steel plates to design stator and rotor, silicon Stator. The stator core uses an isolated thin silicon steel plate that consists of oxide and varnish. Therefore, the hysteresis loss and eddy current loss in the inner magnetic material can be minimized.
c) in ferrite all iron dust powder isolated with epoxy composites materials which is provide excellent ellectro-magnetic effects, compare to steel laminations. hysteresis loss and eddy current losses will be much reduced.
d) I have an experienced in ferrite core chopper/transformers, inductors, coils please note:
If i have a Vicore power supply circuit 2MHZ, and installed xyz core from TDK cores manufacturer, you cannot replace with the exact size of any other manufacturers, until the ferrite materials is 99% accurate, you never get the actual results until the ferrite materials are same as 99%...
e) the shapes of the stator and rotor is also important factor because all present motors are designed on 50, 60 Hz, and 400hz is entirely different construction, if you are using ferrite materials you must apply a more then 500Hz for good result, please search on Google iron core, ferrite core and air core frequencies range, mutal induction etc...
f) also am interested to work on these...
Thank you
Regards
Jaan

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Re: Ferrite as a stator material?

Post by ridethelightning » Jun 28 2019 4:59am

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Re: Ferrite as a stator material?

Post by stan.distortion » Jun 28 2019 4:25pm

Capo_au wrote:
Dec 18 2018 8:39pm
I know i'm a little late to the conversation but I might be able to shed a little light on the topic. As was mentioned above, ferrite only makes sense for high frequency applications where minimising core losses are your main concern. This is because of its low saturation magnetisation, which is typically less than 0.5 T for soft ferrites, will greatly limit the torque density of an electric motor compared to Fe-Si steel laminations.

Amorphous materials like those produced by Metglas have been investigated for use in electric motors.

The main benefits are:
  • The method of production (melt spinning) means they have an inherently low thickness of around 25 microns, which helps reduce corelosses
  • Their low coercivity of ~1 to 3 A/m helps minimise hysteresis losses.
  • A relatively high electrical resistivity when compared to Fe-Si steels, which helps minimise eddy current losses
The downsides are:
  • Amorphous materials are expensive to produce and expensive to stamp out due to their high hardness and high ductility
  • They typically have a very high saturation magnetostriction (shape change upon polarisation), making them noisy when used as an electric motor
  • Their saturation magnetisation at room temperature is only around 80% that of Fe-Si (3wt%) steel. It also falls off quickly as the temperature is raised
  • Their maximum service temperature is relatively low
  • Due to their low thickness the lamination stacking factor also tends to be quite low compared to Fe-Si steel lamination, further reducing a motors torque density.
I'm a materials engineer who develops soft magnetic materials for a living so feel free to pick my brain on the topic :thumb:
Is carbon fibre suitable for a core material or are there any lightweight options? Thanks.

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