liveforphysics
100 TW
This video does a great job of showing why motors have laminated stators.
[youtube]TPijeVdtMIw[/youtube]
[youtube]TPijeVdtMIw[/youtube]
A video showing why motors have laminations.
- Thread starter liveforphysics
- Start date
zap
100 W
Cool video!
I love messing with magnets, showing the neighborhood kids the effects with copper and aluminum.
I don't have enough discipline (or funds!) to goof around with a monster of that size.
I love messing with magnets, showing the neighborhood kids the effects with copper and aluminum.
I don't have enough discipline (or funds!) to goof around with a monster of that size.
Wierd phenomena like that are exactly why so many people get this urge to think magnets are the magic energy solution. :lol:
But it is really cool to see that thing actually pick up and move the aluminum plate, since "everybody knows" that aluminum isn't magnetically reactive.
But it is really cool to see that thing actually pick up and move the aluminum plate, since "everybody knows" that aluminum isn't magnetically reactive.
the reason why motors have laminations is a global conspiracy by the oil companies.
liveforphysics
100 TW
Toorbough ULL-Zeveigh said:
lol
liveforphysics
100 TW
Just in case anyone missed it, the good parts of this vid to see are when he tries to slide the magnet across the sheet of aluminum with about a 1/2" air gap, and you see the heavy sheet of aluminum dragged along with it. This is eddy current resisting the motion of the magnetic field through a conductor. All that friction-like (but not friction obviously) energy loss goes into heating the aluminum as he moves the magnet across it. Picture a motor's rotor packed with magnets trying to spin around a chunk of solid steel... It would be like the motor was packed full of cold peanut butter. If you just increased the power levels to it to make it spin, all the extra energy is going straight into heating the stator.
This is why we like our laminations as thin as possible, and from a metal that conducts as poorly as possible (while still having good magnetic flux guiding properties). Make a stack of a bunch of insulated 0.2mm thick silicon steel laminations, and now those magnets only get a path 0.2mm thick to induct a charge into, making the potential voltage difference very low, and the silicone steel makes the resistance of the steel high to limit the current flow potential from that small voltage difference, and being insulated makes them each behave like a separate unit, so if you've got a 3" thick stator or a 1" thick stator, it only behaves as the sum of the individual lams (rather than getting a huge voltage difference shorting across a wide stator).
This is why we like our laminations as thin as possible, and from a metal that conducts as poorly as possible (while still having good magnetic flux guiding properties). Make a stack of a bunch of insulated 0.2mm thick silicon steel laminations, and now those magnets only get a path 0.2mm thick to induct a charge into, making the potential voltage difference very low, and the silicone steel makes the resistance of the steel high to limit the current flow potential from that small voltage difference, and being insulated makes them each behave like a separate unit, so if you've got a 3" thick stator or a 1" thick stator, it only behaves as the sum of the individual lams (rather than getting a huge voltage difference shorting across a wide stator).
Thud
1 MW
I thought Eddie was the dog on the Fraiser show......
that is an awsome magnet the guy was playing with.....I would crush a finger for sure with that hog......or it would fly through the wall on its way to mate with th lathe! I had a stack of motor magnets in my pocket & ripped my Jeans when i got latched onto the macine....candid camera moment.
that is an awsome magnet the guy was playing with.....I would crush a finger for sure with that hog......or it would fly through the wall on its way to mate with th lathe! I had a stack of motor magnets in my pocket & ripped my Jeans when i got latched onto the macine....candid camera moment.
liveforphysics
100 TW
Thud said:
Yeah, when I just saw the guy pick that magnet up, I was thinking, hmm... danger! danger! You get a little too close to something steel with that, and they are going to touch, even if your fingers/hand etc was between them to begin with.
It still will be between them...just no longer attached to the rest of your body.
The good news is taht the more powerful the magnet, the closer it holds the field lines, so at least it probably isn't going to pull your fridge out of the room next to you. :lol:
If you had the same magnetic capacity in a looser-field magnet, like the old ceramic speaker magnets, it could affect things much farther away than a few inches....
The good news is taht the more powerful the magnet, the closer it holds the field lines, so at least it probably isn't going to pull your fridge out of the room next to you. :lol:
If you had the same magnetic capacity in a looser-field magnet, like the old ceramic speaker magnets, it could affect things much farther away than a few inches....
Microbatman
1 kW
liveforphysics said:
Agree Thanks for pointing this Important variable out.
Anyone know what thickness the laminations are on the Crystalyte X5 series?
Is the X5 a "cast" stator?
What about the lamination thickness on the 9c series?
Still looking for that .2mm thick N45+ mag direct drive motor. Preferably in an Axial rather than radial design.
.
.
Jeremy Harris
100 MW
One consequence of eddy current loss (and the subsequent heating effect) caused me some angst on the first prototype boat outrunner propulsion unit I made. To protect the motor and controller from getting wet I put them inside an alloy box. Unfortunately, the box I used was a bit small, so the clearance between the outrunner bell and one inside face of the alloy box was only around 1mm (I actually had to use the Dremel to grind the inside out to stop the motor touching in places).
I didn't notice any particular problem when bench testing (with the case off), but when I ran the motor at speed on a boat the case soon started to get pretty hot, almost too hot to touch after about ten minutes or so. I couldn't understand where the losses were coming from at first, because whenever I took the case off to bench test the motor everything seemed fine. It was only when I went to slide the case on when the motor was running that I felt the drag and realised I'd been a complete plonker............
This is worth knowing about if you're fitting an outrunner close to anything metallic. There's enough rotating leakage flux coming through the outside of the can to cause potential problems if you have anything metallic within about 10mm or so of it. My present set up uses a much bigger alloy box, with the motor well clear of the case, and doesn't seem to suffer any additional losses from eddy currents, as far as I can tell.
Jeremy
I didn't notice any particular problem when bench testing (with the case off), but when I ran the motor at speed on a boat the case soon started to get pretty hot, almost too hot to touch after about ten minutes or so. I couldn't understand where the losses were coming from at first, because whenever I took the case off to bench test the motor everything seemed fine. It was only when I went to slide the case on when the motor was running that I felt the drag and realised I'd been a complete plonker............
This is worth knowing about if you're fitting an outrunner close to anything metallic. There's enough rotating leakage flux coming through the outside of the can to cause potential problems if you have anything metallic within about 10mm or so of it. My present set up uses a much bigger alloy box, with the motor well clear of the case, and doesn't seem to suffer any additional losses from eddy currents, as far as I can tell.
Jeremy
liveforphysics
100 TW
Jeremy Harris said:
OMG! Now it seems so obvious, but you just helped me realize why my no-load current is 1.5amps higher when the motor is bolted to my mounting bracket than when it's off the bike on the test bench! I hadn't even given it much thought, but that's ~100w of waste heating I could get out of the system. LOL! Thanks for the mental swat on the head my friend.
I wonder if this could be an effect with any consequence on hub motors in close-clearance forks? Or if it makes a difference to heating of the motors because of the cast motor centers (not the lams but what the lams/etc are affixed to)?
How would one be able to test for this kind of issue?
I know some motors use laminated construction all the way to the axle, like my cieling fan motor (rewound to become a BLDC eventually, once I can get magnets for it). Would those theoretically have lower losses of this type than the hub motors that only have laminates at the windings, but solid metal inside that radius?
What we need is a camera that can see magnetic fields just like IR or light or whatever.
How would one be able to test for this kind of issue?
I know some motors use laminated construction all the way to the axle, like my cieling fan motor (rewound to become a BLDC eventually, once I can get magnets for it). Would those theoretically have lower losses of this type than the hub motors that only have laminates at the windings, but solid metal inside that radius?
What we need is a camera that can see magnetic fields just like IR or light or whatever.
liveforphysics
100 TW
amberwolf said:
Do a no-load RPM test with the motor clamped to a piece of wood or something, then do a no-load test with it mounted in the bike. Fortunately, I think it would be pretty mild loss because the forks/stays aren't quite in the axis that is prime for making eddy losses.
amberwolf said:
I think as long as the flux limits of the stator tooth aren't near saturation, then the eddy current induction area is pretty contained in the tooth and tooth back iron ring, so the eddy losses dont reach the core material the stator lams are bonded upon, but I'm no expert.
So it's only those madmen overvolting and amping their hubs that would probably have to worry about that? :lol:
I'd guess that if it's got enough power being pulled thru it that it could get saturated, and at that point it'd begin showing this type of problem?
Regarding the test on wood blocks, I was also thinking of the hub's own case interfering with the stator fields, causing some heating (though this might not be as bad with the fields switching on and off so fast?).
I guess one could make plastic covers out of machined lexan or delrin or polycarbonate or whatever, replace the metal ones, and try it out. Since the test would not have to be with the bike bearing weight, just on a test stand, it should be ok stress-wise I'd think.
I assume the current drawn would also go up if there are eddy losses happening?
I'd guess that if it's got enough power being pulled thru it that it could get saturated, and at that point it'd begin showing this type of problem?
Regarding the test on wood blocks, I was also thinking of the hub's own case interfering with the stator fields, causing some heating (though this might not be as bad with the fields switching on and off so fast?).
I guess one could make plastic covers out of machined lexan or delrin or polycarbonate or whatever, replace the metal ones, and try it out. Since the test would not have to be with the bike bearing weight, just on a test stand, it should be ok stress-wise I'd think.
I assume the current drawn would also go up if there are eddy losses happening?
dak664
1 kW
- Joined
- Aug 17, 2008
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A similar inductive loss can occur where a wire carrying AC current enters a metal electrical box. If it is paired with the return wire the magnetic fields tend to cancel, if not paired the losses can be as high as a few watts per amp. If you ever find a warm electrical panel check the cables with a clamp-on ammeter for unpaired currents. Probably why you don't see hub motors with power leads coming out both sides of the axle.
Jeremy Harris said:
some types of plastics too.
Really? Is it because of the carbon content and structure, or is it from metallic additives?
liveforphysics
100 TW
SoSauty said:
Many inrunners (maybe all?) have enough flux leakage you can trigger your hall sensors from the outside of the case just by taping them onto it.
This means, the more conductive material on the outside, the more waste heat, lower efficiency, etc.
Somebody with a bunch of inrunners and heatsinks should try to quantify the amount lost to see if it's trivial or significant.
salty9
1 kW
I can remember a monster horseshoe magnet in our freshman physics class that demonstrated magnetic flux clearly. If a penny was pitched toward it at the right speed and distance the penny would move in a circular arc. My best effort was almost 180 degrees.
jonescg
100 MW
This is interesting... I have a lot of aluminium around my motors - the plates they are bolted to, and the frame of the bike...Hmm, next bike is going to be a carbon fibre one, with carbon fibre mounting brackets and carbon fibre bolts...
liveforphysics
100 TW
jonescg said:
Carbon fiber conducts pretty damn well. Fiberglass, bakelite, kevlar, poly-carb, etc would be the path to take for things near spinning magnetic fields.
jonescg
100 MW
So do you reckon my motor plates will present a significant loss?
liveforphysics
100 TW
Nope.
It's brushed, so the perm magnets are bonded to the iron backed flux plate that stays stationary to the aluminum plates. You could only be getting losses from the flux that leaks off the rotor, but those axial flux motors are pretty damn good about keeping the flux in the flux gap.
I think you're good-to-go.
If that was a giant outrunner brushless motor or something, then you would be hosed.
It's brushed, so the perm magnets are bonded to the iron backed flux plate that stays stationary to the aluminum plates. You could only be getting losses from the flux that leaks off the rotor, but those axial flux motors are pretty damn good about keeping the flux in the flux gap.
I think you're good-to-go.
If that was a giant outrunner brushless motor or something, then you would be hosed.
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