View Full Version : Remagnetizing stepper motor rotor

04-11-2004, 02:33 AM
Actualy I am not shure this is the right forum to post this but anyway.

So I took the rotor out of the stator and do not even know the specs of the stepper. 86 mm diam motor.
From seeing the rotor it looks like somethin metallic, definately not neodimium but more like AIN. How many poles do a rotor has?

I have 25 NeFb magnets grade 35, dimentions 2"x1"x0.5" for a windturbine project. Supposing if the rotor has 4 poles N S N S
I could arrange 4 of my neodimium magnets like this, just in the entrance of the stator,

. N
. |
S- -S
. |
. N

so when I introduce the rotor back in the stator, the neodimium magnets will remagnetize the rotor.

I guess I could find out the number of poles with a small magnet, I would have to take the rotor out again though. When I had my rotor outside I tested the magnetic field by getting close a small washer and the magnet wasnt very strong either.

A specialized rewinding shop could reassemble a motor and remagnetize it based on original specifications, but I dont know the specs of my motor anyway.

04-11-2004, 08:59 AM
If it's a stepper the magnet usually have one pole each end with something that looks like a gearwheel at each end. The teeth are staggered on these 2 wheels. I don't think you can remagnetize it with the magnets you have. Reassemble it and see how it performs. I''ve tried disassembling a couple of motors before I knew this (bad excuse, I'm curious enough to do it anyway). One, a small one from an old 5,25" floppy drive seemed to survive without any noticeable loss of torque. The other one a 90oz/in SlowSyn is definately junk. Almost total loss of torque.

You probably have difficulties measuring the torque, but try this: Chuck the axle of a known good motor of exactly same type in your lathe. Connect a VOM across one winding measuring VAC. Prevent the motor case from turning then start your lathe and record the voltage. Do the same with the questionable motor. If about the same voltage then the magnets are also about the same strength. The voltage measured will be proportional to speed, magnet strength, number of winding turns and also frame and other construction features. Due to these last mentioned, the 2 motors need to be the same type.

When you say there was not much magnetism, maybe it is not. Some steppers (variable reluctance) don't have magnets. Easily recognizeable in that they don't have any detent torque, and will output almost no voltage in the above test.

04-11-2004, 09:47 AM
I have dismantled a 5.25 floppy stepper as well and seen those gear like dents. The one I want to remagnetize is from this thread Help to identify this stepper" (http://www.cnczone.com/forums/showthread.php?s=&threadid=3863) . The rotor of this stepper has no dents and its very flat.