loss of magnetism in permanent magnets

THE_RB

Joined Feb 11, 2008
5,438
Yes I think your quite right there is a possible repulsion as the stator N drags the rotor S there will be a stator S pushing the rotor S.

It's been 30 years since I sat in the classroom doing DC machines theory but from memory the rotor will align almost perfectly with the unlike stator pole at light loads, (ie N to S) and then is only deflected a small amount under normal loads, so the magnetic field lines closely link the pulling N pole with the S rotor pole being dragged very slightly behind it.

To answer you question, I guess when the PM motor is off the iron stator acts like a "keeper" and helps the PMs retain their magnetism. Then when running there is a very high field strength through the stator and through the rotor from N to S etc, and very little if any opposing of N to N poles. That picture you posted in #17 shows the field path of the strongest magnetic field lines.

Maybe an expert will chime in here as I'm far from being an expert in DC machines!
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
Ok, so Amilton posted a video in another thread that confirms my repulsion theory (time: 5:08 to ~6:20).

So I guess my theory now hinges on 1 question:
If holding permanent magnets in opposition depletes them, does holding them in attraction charge them at the same rate, so that the net charging/depleting forces are zero?
 

THE_RB

Joined Feb 11, 2008
5,438
That would be my understanding.

But with the extra thought that the pushing and pulling forces are not always going to be even as the unlike poles will stay relatively closely locked, so the majority of "lines of force" of the field are in the forward direction through any permanent magnets.

So in your words there is probably more of the "charging force".

Forget permanent magnets for a moment and think more of the design of solenoids.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
Ok thanks RB and all, I think I get it now. I think you're right; most of the force put on the magnets would be in the unlike poles direction (or charging as I said) .
 
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