Re: [CAD_CAM_EDM_DRO] A little experiment on demagnetization

I seem to remember that dc servomotors fitted with Alnico magnets suffered
from the same problem of demagentisation. However the way to overcome it is
using a keeper (ring shaped piece of iron) that is slid into the space
vacated by the rotor as the rotor is removed.

Ferrite magnets don't suffer and motors fitted with them can be disassembled
without a problem.

In both cases the real problem is the physical problem of being able to pull
the rotor out and replace it without damaging the magnets or picking up
particles of magnetic material that jam the airgap.

There is a magnetic reason for all this - permeability, remnance and all
that stuff!!

regards Peter

----- Original Message -----
From: <mariss92705@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, February 04, 2003 4:45 PM
Subject: [CAD_CAM_EDM_DRO] A little experiment on demagnetization


> Hi,
>
> When I don't know for sure, I run an experiment:-)
>
> 1) I took two identical motors, (Rapidsyn 23D6209, 4.7A @ 1.7VDC)
> connected in full-winding mode and set the current to 2.4A per phase
> on a G201. The power supply was 25VDC.
>
> 2) I removed the rotor from one motor, waited 5 seconds, then
> replaced it. The other motor was unmolested and would serve as the
> baseline unit.
>
> 3) Both motors were then run on a dyno and data was taken at 5 revs
> per second (1,000 full steps per second).
>
> 4) The baseline motor delivered 18.25W to the dyno at that speed for
> a torque of 82.3 in-oz.
>
> 5) The molested motor delivered 11.75W for a torque of 52.9 in-oz.
>
> 6) The calculated torque (and power) output for the disassembled
> motor was 64% of the intact motor.
>
> 7) I removed the rotor again, leaving it out overnight before
> reassembling it for the second time and ran the above tests again.
> There was no additional deterioration in performance.
>
> Conclusions:
>
> 1) Demagnetization occurs immediately on disassembly.
>
> 2) The motor loses about 1/3 of its holding torque and and power as a
> consequence.
>
> This experiment applies to standard magnet motors. I have not tried
> it on the newer, rare-earth magnet motors. I like the ones I have too
> much to find out. Any volunteers?
>
> Mariss
>
>
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