DC Motor Magnet Lifespan

Thread Starter

KCHARROIS

Joined Jun 29, 2012
302
Hello,

I will be machining something similar to a DC motor but will only turn 180 degrees. I will have a coil in the centre and 2 magnets on the rotating piece. So my question is without considering wear and tear on everything but the magnets, how long until the magnets lose their magnetic strength or should it even be considered? And what about 2 magnets facing each other north - north or south - south?

Thanks,
KCHARROIS
 

Dr.killjoy

Joined Apr 28, 2013
1,196
Hello,

I will be machining something similar to a DC motor but will only turn 180 degrees. I will have a coil in the centre and 2 magnets on the rotating piece. So my question is without considering wear and tear on everything but the magnets, how long until the magnets lose their magnetic strength or should it even be considered? And what about 2 magnets facing each other north - north or south - south?

Thanks,
KCHARROIS
Pics help out a lot ..
 

GopherT

Joined Nov 23, 2012
8,012
Shouldn't need a picture, just imagine a normal dc motor... What is the lifespan of a magnet in that motor, meaning until it has no magnetic strength?
I was just using some motors with perm magnets over 30 years old from an old HP pen plotter. No problem. Some degrade over time but that is because of oxidation I would guess (or demagnetized by something else). Most permanent magnets you buy today are made with pretty good technology to prevent oxidation or other issues - they will last 10+ years.
 

MaxHeadRoom

Joined Jul 18, 2013
19,430
Most of the rare earth magnetic materials retain there magnetic field for many decades (or more), some of the earlier motors recommended that a iron keeper be inserted when removing the armature, but I have not had that problem.
Max.
 

MrChips

Joined Oct 2, 2009
19,753
Permanent magnets are, well, permanent.

If you subject a magnet to high temperatures or physical shock the magnetic domains can randomly realign themselves and thus reduce the overall strength of the magnet.
 

Glenn Holland

Joined Dec 26, 2014
684
The life span of magnets depends on the material and also the conditions in which they operate such as a motor, lifting magnet, or a magnetic holding table such as those used on a surface grinder.

Alnico can experience accelerated decay (demagnetization) if the reluctance is cycled (by repeatedly increasing and decreasing the air gap) or subjected to an opposing field. Ceramics are better, but they can be demagnetized if misused by cycling the air gap. This commonly occurs when people play with magnets by sticking and removing ferrous objects. "Rare Earth" magnets are extremely rugged and they are used in applications with very high opposing fields such as motors.

In all cases, if a magnet is to be used for a critical application that requires constant flux, keep it away from ferrous objects until it is ready for installation in the final product.
 

Thread Starter

KCHARROIS

Joined Jun 29, 2012
302
Most of the rare earth magnetic materials retain there magnetic field for many decades (or more), some of the earlier motors recommended that a iron keeper be inserted when removing the armature, but I have not had that problem.
Max.
Great! Thanks for the replies. I guess its safe to say if i remain at normal room temp and have no corrosion they should last over ten years. So the second part now is what if I have a 2 magnets positioned facing each with the same poll like north and north or south and south. Will this degrade there magnetic strength quickly? Or is it likely that one magnet's poll's will change?
 

MaxHeadRoom

Joined Jul 18, 2013
19,430
This is the condition in most DC motors that poles alternate around the stator. So you end up with poles opposing on either side.
The only motors I have heard of that seem to suffer when dismantled for some reason is Stepper motors.
Max.
 
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