How long do magnets keep their power ?

[Bazaki]

I wonder if our Ebike HUB motors will get less power after a while.

After 3000 km's km my Crsytalyte HS3540 still rides as new but if I install a brand new motor it "feels" a bit faster.

If a motor sits on the shelf for 5-10 years would the motor have less performance due to the magnets that will loose their power ?
And would there be difference between sitting on the shelf or ride it every day ?

On the other hand, you can still find old industrial DC motors from 1960 and they also still spin around.

My old '54 Chevy 3100 startermotor can be still original and delivers still enough power for it's job. 8)

 

[fechter]

NdFeB magnets can retain their magnetism for something like thousands of years if they are never overheated. If the magnets are subjected to excessive temperature, they can lose their power immediately.

 

[neptronix]

^--yup

A lot of us are overheating our hub motors. How many of you run your motor at the factory rated power of 500-1000W? continuous :lol:
It's those times where the magnets hit 80c-120c - that period just before the enamel starts melting off the copper on the stator - that they take damage. This damage can add up over many many rides.

I managed to slightly demagnetize my MAC motor running it up a 5-7% 2 mile continuous grade dumping 1600W into it at half it's loaded speed. I had been fairly nice to the motor before then. The motor got very hot and certainly lost some of it's poke, and efficiency. As the neo magnets wear, the more heat the motor makes.. and you can have kind of a cascading failure of sorts.

This is why it's important to not push a motor too hard over it's factory rated specs. The magnets should be strong for a long time if you run the motor closer to it's specs.

 

[sn0wchyld]

^--yup

A lot of us are overheating our hub motors. How many of you run your motor at the factory rated power of 500-1000W? continuous :lol:
It's those times where the magnets hit 80c-120c - that period just before the enamel starts melting off the copper on the stator - that they take damage. This damage can add up over many many rides.

I managed to slightly demagnetize my MAC motor running it up a 5-7% 2 mile continuous grade dumping 1600W into it at half it's loaded speed. I had been fairly nice to the motor before then. The motor got very hot and certainly lost some of it's poke, and efficiency. As the neo magnets wear, the more heat the motor makes.. and you can have kind of a cascading failure of sorts.

This is why it's important to not push a motor too hard over it's factory rated specs. The magnets should be strong for a long time if you run the motor closer to it's specs.

Not quite right. Neo magnets start loosing their power at temps north of 80deg c, though some magnets are stable as hugh as 150c. However, they do not keep loosing more flux for each trip north of their original max temp rating. If you loose some strength going to 90 deg on 80deg max mags for example, youll end up with weaker magnets, but theyll now not loose any more strength untill you go hotter than 90. Effectively giving you weaker magnets by a few% but with a higher temp rating.

I did read too that one guy tested some neos after 10years of use, theyd lost less than 1% of their strength, so yea... Not enough to loose sleep over.

 

[Arlo1]

I've over heated the PISS out of my motor many many times. I melted the solder off the hall sensors and nothing the magnets are just like they were when I first got the motor. Luke has fried hall sensors in a golden motor as well and still no issues. You will most likely have other issuses before you hurt your magnets.

 

[salty9]

Check http://www.rcgroups.com/forums/showthread.php?t=307133&highlight=gauss

In addition to showing how to make a Gauss meter it also discusses heat effects, demagnetization and remagnetization.

 

[neptronix]

Not quite right. Neo magnets start loosing their power at temps north of 80deg c, though some magnets are stable as hugh as 150c. However, they do not keep loosing more flux for each trip north of their original max temp rating. If you loose some strength going to 90 deg on 80deg max mags for example, youll end up with weaker magnets, but theyll now not loose any more strength untill you go hotter than 90. Effectively giving you weaker magnets by a few% but with a higher temp rating.

I did read too that one guy tested some neos after 10years of use, theyd lost less than 1% of their strength, so yea... Not enough to loose sleep over.

Okay, sounds like you know a bit more than me. My MAC motor has felt like it progressively lost power, then again, i did progressively put more and more power into it , so that explains.

Anyway i doubt any of our motors have 150c rated magnets. So 100c is prolly a safe estimation, no?

 

[sn0wchyld]

Not quite right. Neo magnets start loosing their power at temps north of 80deg c, though some magnets are stable as hugh as 150c. However, they do not keep loosing more flux for each trip north of their original max temp rating. If you loose some strength going to 90 deg on 80deg max mags for example, youll end up with weaker magnets, but theyll now not loose any more strength untill you go hotter than 90. Effectively giving you weaker magnets by a few% but with a higher temp rating.

I did read too that one guy tested some neos after 10years of use, theyd lost less than 1% of their strength, so yea... Not enough to loose sleep over.

Okay, sounds like you know a bit more than me. My MAC motor has felt like it progressively lost power, then again, i did progressively put more and more power into it , so that explains.

Anyway i doubt any of our motors have 150c rated magnets. So 100c is prolly a safe estimation, no?

I doubt its much more, if any lol.

no one on es knows the ratings on the magnets in our motors (atleast the common ones like cristalite/9c etc) so most go with the minumum of ~80C. going to 90C though from what I've read will make bugger all difference, you might loose 3 or 4%, maybe less. You're KV will actually go up by the same % too, so you'll get a slightly faster but lower efficiency motor. probably not enough to notice though.

And yea, if you're putting more power into a motor that's already overheating, then its gonna keep overheating by bigger and bigger margins, as your kv goes up (so low speed efficency goes down) as well as your peak (and overall) efficiency falling too. I'd think there's something else going on though, perhaps your bearings are shot, or the gears are causing more friction than when new... far more likely than damaged magnets.

What I found interesting is that the shape of the magnets had a significant influence on the temperatures they could handle. the flat type ones like in hub motors are the most susceptible to heat damage, where as the narrower/thicker style ones like those found in 80100 out runners and similar can handle much higher temperatures, in excess of 110. This is all on a simulator though, I've done no real world testing to confirm it.

 

[neptronix]

Actually my 38 volt loaded RPM went up from ~320RPM when i first bought it to ~360RPM.
And it does have less torque as well.

It does not cruise at a faster speed per volt, but the powerband after cruising speed to unloaded speed seems longer.
For example, i was pedaling probably at 120-140 cadence or something crazy going down a hill and on 12S nominal voltage ( 46.5v-ish), i usually cruise at around 29mph on the flats, and can pedal up to about 31-32mph, but i was hitting 38mph! and the motor still contributed a little bit of power at that point

 

[Bazaki]

But what about some kind of magnet motor ? I thought these magnet motors can work, but only for a few hours since the magnets are out of power.
Or are all of these fake ?
https://www.youtube.com/watch?v=usGzQFKOEfM

 

[bigmoose]

Here's a little chart on Neo magnet properties. Max use temps, Currie temps, and a few others:

 

[Spacey]

Ok so this hurts my brain, where does the power come from natural earth magnets. How can it be able to apply a force constantly with no fuel....brain hurts.

 

[bigmoose]

Ok so this hurts my brain, where does the power come from natural earth magnets. How can it be able to apply a force constantly with no fuel....brain hurts.

Spacey, you are pondering the foundational wonders of the universe! For I too feel that magnetism is in the realm of electrostatic, strong nuclear, weak nuclear, and gravitational forces. We can describe them, and their effect upon nature... but what are they really? I personally do not think any human knows...

This link may help with the basis of permanent magnetism:
http://en.wikipedia.org/wiki/Dipole

 

[John in CR]

But what about some kind of magnet motor ? I thought these magnet motors can work, but only for a few hours since the magnets are out of power.
Or are all of these fake ?
https://www.youtube.com/watch?v=usGzQFKOEfM

It's the initial force put into them that gets the spinning going, which is why they all eventually stop, making them effectively a good hybrid bearing, not a motor.

 

[amberwolf]

Ok so this hurts my brain, where does the power come from natural earth magnets. How can it be able to apply a force constantly with no fuel....brain hurts.

Naturally-occuring magnets are typically very weak, and usually get their magnetism from the Earth's own field, as they cool from molten or otherwise-sufficiently-heated material containing iron/etc., and the crystals that form in them self-align to the Earth's magnetic field as it exists at the time. If the field is strong, it induces a stronger field in the material, and if it is weak, the induced field is weaker.

The Earth's own field's power comes from the rotation of the Earth itself, and the heat within the planet, both of which originally came from the kinetic energy of the materials in the planetary nebula that the solar system formed from, as it collapsed from it's own gravity, and from the kinetic energy of collisions of bodies and particles since that time.

So none of hte energy was "free", it all came from somewhere, going back to the origin point of the universe itself. Past that point, who knows?

 

[fechter]

Spacey, you are pondering the foundational wonders of the universe! For I too feel that magnetism is in the realm of electrostatic, strong nuclear, weak nuclear, and gravitational forces. We can describe them, and their effect upon nature... but what are they really? I personally do not think any human knows...

Quite true. Nobody even has a remote clue how gravity works. I think all these fields are interrelated. The relation between magnetic and electric fields is well explored, but I think all the fields interact with each other in a similar fasion. To me, there is one more field: momentum. Momentum exists everywhere and can exert forces on matter just like the other fields. Gravity waves are really probably gravity-momentum waves and some theorize they travel at the speed of light squared (that's really really fast).

Now back to the magnets, the 'power' of a permanent magnet is not really creating or expending energy. It can simply store some like a spring or rubber band. You won't ever get more out of it than was put into it orginally.

 

[Toorbough ULL-Zeveigh]

Or are all of these fake ?
https://www.youtube.com/watch?v=usGzQFKOEfM

wow, did you realize by an amazing synchronicity the answer that the OP is looking4 was to be found buried in the comments of that utube vid?

Een Neodynium Magneet verliest 1% kracht in 100 jaar.

here is some quantitive data if your interested.

 

[athlon]

Ok so this hurts my brain, where does the power come from natural earth magnets. How can it be able to apply a force constantly with no fuel....brain hurts.

force is not power , there is no need of fuel to make a force , there is need of fuel to create power , power is a force times travel.

think aobut the magnet as a hill , when you go uphill the hill repels your bike with a force , but if you leave the hill alone for many years this will not make this force weaker.


Demagetization occurs when you overhead your magnet and the loos ther strenght .

 

[kennybobby]

Ok so this hurts my brain, where does the power come from natural earth magnets. How can it be able to apply a force constantly with no fuel....brain hurts.

i'm gonna guess that you were probably really interested in the high strength "rare earth" magnets since that is what is used in most of the newer BLDC motors, and not the weak 'natural' ones and the earth's magnetic field,--there are no real motors use naturally occuring magnets.

So the energy or 'power' for these man-made magnets comes from the initial magnetization. The metal is formed into the desired shape and has no magnetic field. Then the blank is put into the chamber of a device which applies a very strong magnetic field along the desired field axis which aligns the metal and creates the 'permanent' magnet. The chamber's strong field comes from the volts and amps applied to the coils in the chamber and Power = volts x amps...

 

[boostjuice]

The Magnet Manufacturing Process