1. May 21, 2010

### SciencePF

Hello!
What is the lifetime of a permanent magnet? How we calculate it?
Thanks

2. May 21, 2010

### Rajini

I think there is no formula to find such a lifetime for permanent magnets.
Magnets (i mean the normal one found in loud speakers, fridge doors, horse shoe) doesn't loss its magnetic property significantly over time. The factor that influence lifetime are: temperature, shock (& hitting), placing magnets such that north facing close to north of other magnet, etc.
But magnetic properties due to electron stays forever.

3. Apr 2, 2011

### satya98

How far we can generate electricity from a rare earth magnet(permanent)?

4. Apr 2, 2011

### JaredJames

Do you mean how much can we generate with a permanent magnet or how long for could we generate before it loses it's magnetism?

5. Apr 2, 2011

### Antiphon

Indefinitely. The energy doesn't come from the magnet. It comes from whatever is pushing the magnet near a wire.

6. Apr 2, 2011

### JaredJames

So the magnetism of a natural magnet never dies off? It doesn't have a life span?

7. Apr 2, 2011

### pallidin

From an earlier PF post of mine:

"In your context, magnetism, such as with a magnetized iron bar or neodymium(for example) composition DOES have a "lifespan"

A "magnetised" iron bar effects a "dissorientation" that is not "normal"
In time, the iron bar will re-orient into a non-magnetic, normal state.

Not sure about the figures, but I recall that it is somewhere around 300+ years for an "iron" magnet, and several thousand(perhaps 10's of thousands) for neodymium.
Again, I may have my figures wrong in exact detail, but nonetheless, YES... there is a "lifespan"

Source: https://www.physicsforums.com/archive/index.php/t-121135.html

8. Apr 2, 2011

### davenn

yes but you are referring to iron that has been magnetised and thats fair comment :)

but for naturally occurring magnetic iron or other rare earth minerals its more likely to be indefinately

We can (in geology) measure paleomagnetisim in rocks ging back 10's and more of milions of years

Dave

9. Apr 3, 2011

### satya98

I did'nt get u correctly. wat my question is how long the electricity can be generated from a permanent magnet.
For suppose I am generating electricity from a permanent magnet by shaking(lenz's law). How long I can generate electricity by this process if I shake it for a life time

10. Apr 3, 2011

### JaredJames

11. Apr 3, 2011

### satya98

I am working on project regarding this concept. If , what we thought is true, then a generator of life time validity is going to be invented

12. Apr 3, 2011

### JaredJames

How is that?

Natural magnets are no where near as useful for power production as electromagnets. Far too weak.

You also still have the problem of bearings wearing out and other components failing. The magnets are only a small part of the overall system.

I get this twitch in my neck every now and then. I've found it's a good indicator of when a topic is about to hit the realms of perpetual motion machines. And here it comes again...

13. Apr 3, 2011

### Neight

I was actually wondering the same thing about rare earth magnets, so thanks for posting this question. and it's not about perpetual motion :P looking into the validity of Bedini SSG motor to play with. don't care about perpetual motion, just interested in how much actual work you can get from that kind of a system, short of part failure. i read somewhere the opposing magnetic forces would "blow away" the magnetism of a magnet.
trying to verify if that is true or not.
(though i have to admit, it is pretty funny to read these kinds of posts and see everyone groan when there is a suggestion of perpetual motion, i can almost hear your headaches starting :P)

14. Apr 3, 2011

### Neight

I was actually wondering the same thing about rare earth magnets, so thanks for posting this question. and it's not about perpetual motion :P looking into the validity of Bedini SSG motor to play with. don't care about perpetual motion, just interested in how much actual work you can get from that kind of a system, short of part failure. i read somewhere the opposing magnetic forces would "blow away" the magnetism of a magnet.
trying to verify if that is true or not.
(though i have to admit, it is pretty funny to read these kinds of posts and see everyone groan when there is a suggestion of perpetual motion, i can almost hear your headaches starting :P)

15. Apr 3, 2011

### JaredJames

I can't find a wiki page (or anything short of sites screaming crackpot) on this "Bedini SSG motor".

From the few items I have seen, it looks like a load of non-sense and some variation of a PMM. However, without something in detail on it I can't say one way or the other.

16. Apr 3, 2011

### pallidin

From: http://www.eamagnetics.com/gen_faq.asp#How_long_will_a_permanent_magnet_last

How long will a permanent magnet last?

A permanent magnet will retain its magnetism unless it is affected by a strong outside magnetic or electrical force, or elevated temperatures. If they are not exposed to any of these conditions, permanent magnets will lose magnetism on their own, however this degradation is very slow, on the order of one percentage point every ten years or so.

17. Jun 10, 2011

### scotia

What, if anything, would cause a permanent magnet to lose its 'power' over time? Would it eventually be reduced to zero, even if only in theory?

18. Jun 10, 2011

### pallidin

"...The length of "life" of a permanent magnet depends on many factors. When the domains are randomized again, the material will cease being magnetic, but this can be a very gradual process. This re-randomizing is affected by several things. The higher the temperature, the faster this process will happen..."

Source: http://education.jlab.org/qa/permmagnet_01.html

19. Jun 10, 2011

### rollcast

If you intend to use it in a generator as it will be generating a current in the stata coils there will be a magnetic field formed in these that will oppose the field of your magnets. this will very very very slowly degrade the magnet, probably the earths magnetic field would have more of an effect.

All depends on the size of the stata coils and the strength of the magnet