Electromagnet Strength vs Permanent Magnet Strength

Thread Starter

DefaultZero

Joined Apr 19, 2018
4
Hello,

Here is what I am comparing.
12v 500 Newtons Electromagnet with a 12V 2A power supply.
N45 150 Newtons 1.5" x 1/4" Neodymium Disc Magnet

When I compare the two magnet's strength, I find that the neodymium magnet is much much more powerful especially from a distance.
The electromagnet seems to work only at really close distances.
I initially thought this had something to do with the circuit I had with the electromagnet, but I removed basically everything and now just have the power supply plugged straight into the electromagnet. No difference.

Would anyone know why this would be? Why are the force ratings of the neodymium are 1/3 of the electromagnet, but yield maybe 4-5x the perceived strength, especially from a 2" distance?

Thank you,
 

AlbertHall

Joined Jun 4, 2014
12,072
It may because of the physical arrangement of the two magnet systems.
The permanent magnet has its poles on opposite sides so the lines of force go all the way round the magnet from one side to the other. hen the magnet is stuck to something the lines of force still have to go through the air to get to the other pole.
The electromagnet is lik a 3D U shape so both poles are on the same side. The lines of force just hop from one to the other and when it is stuck to something the magnetic path is completely closed - no air gap in the path.
 

BR-549

Joined Sep 22, 2013
4,928
I wouldn't count on the specs. Does it take ~100 lbs of force to remove electro?

And you might compare the difference in area.
 

Thread Starter

DefaultZero

Joined Apr 19, 2018
4
When attached to a solid steel surface, does the electromagnet still appear weaker than the neodymium one?
I did not measure it, but when I attached a steel brick to electromagnet, it was really tough to pull it off. I could probably say that it felt like a stronger pull when the steel brick was connected when comparing the permanent magnet the same way.

I'll need to setup some scales and test them out.
 

Thread Starter

DefaultZero

Joined Apr 19, 2018
4
It may because of the physical arrangement of the two magnet systems.
The permanent magnet has its poles on opposite sides so the lines of force go all the way round the magnet from one side to the other. hen the magnet is stuck to something the lines of force still have to go through the air to get to the other pole.
The electromagnet is lik a 3D U shape so both poles are on the same side. The lines of force just hop from one to the other and when it is stuck to something the magnetic path is completely closed - no air gap in the path.
Would you happen to have an image of this? The images of magnet visualization I'm finding for both permanent and electromagnets look the same.
But that would explain things if the two magnets behave differently. Thats sorta what I experienced when I tested them at 0 distance. Pulling the steel object off was probably more difficult than with the permanent magnet. Again, I'll need to get scientific and get actual data to prove that.
 

Thread Starter

DefaultZero

Joined Apr 19, 2018
4
I wouldn't count on the specs. Does it take ~100 lbs of force to remove electro?

And you might compare the difference in area.
When sourcing the two magnets, I tried to get the surface areas to be the same.

I guess what I'm beginning to think is that the two magnets just have different shaped magnectic fields. Is this true?
 

BR-549

Joined Sep 22, 2013
4,928
You could get some iron filings and have a peek. The filings should also point out the areas and relative strength of the flux.

The pattern and density of filings will show the stronger magnet without measurement....and quickly.

Edit: You could mix up some Ferrofluid.
 
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AlbertHall

Joined Jun 4, 2014
12,072
Would you happen to have an image of this? The images of magnet visualization I'm finding for both permanent and electromagnets look the same.
But that would explain things if the two magnets behave differently. Thats sorta what I experienced when I tested them at 0 distance. Pulling the steel object off was probably more difficult than with the permanent magnet. Again, I'll need to get scientific and get actual data to prove that.
The one you linked to above looks to be constructed as described here:
https://en.wikipedia.org/wiki/Electromagnet#Closed_magnetic_circuit
 

-live wire-

Joined Dec 22, 2017
956
Here is an interesting graph that explains it well. Just click on the "technical". Compare case 1 to case 3. It shows you that they both decrease exponentially, but with a different ratio. It is not exactly the same thing, but it should give you an idea of why you are experiencing those differences.
https://www.kjmagnetics.com/proddetail.asp?prod=BX8X8C-N52

Or even better, compare case 1 to case 3 here:
https://www.kjmagnetics.com/largergraph.asp?CI=3&pName=BX8X8C-N52
https://www.kjmagnetics.com/largergraph.asp?CI=1&pName=BY0Y0Y0

So try and find more info if you can. Don't just look at the rated pull force under ideal conditions.
 
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