Re: Why do stepper motors lose their magnetism when disassembled?

Hi,

I have a book here that deals with building a coil and using it to
magnatize the ignition components of a Ford Model T, not exactly a
new machine using modern materials. It states that half of the
magnetic force is lost if a keeper is not connected across the magnet
before removing it from the magnetizing coil. If the keeper is not
used the magnet will not generate enough force to make a spark for
the plugs.

It has been my experience the more powerful the magnet, using modern
materials, the more marked the loss of power removing it from the
coil without a keeper.

I have a magnetic chuck which I took to bits and just takin out the
magnets and putting them back made the chuck useless. I will be
building a coil soon to remagnetize them and make sure I use a keeper
to move them from the electro-magnetic coil and while refitting in
the chuck.

I have no interest in getting into the physics I just know it happens
and why.

Regards, Terry

> I don't understand. Keepers are there to prevent demagnetization

that

> takes months or years... and the modern materials like neodymium do

not

> self-demagnetize like the old stuff.
>
> Danny
>
> wotisname wrote:
> > Hi,
> >
> > The reason is very simple. Magnets need a keeper plate to stay
> > magnetized, some magnets loose their magnetism quicker than

others

> > dependent on the material they are made from. When you open a

stepper

> > motor you destroy the keeper which in this case is the motor

armature

> > and casing and half the magnetium effectively escapes, a bit like
> > letting the smoke out of electronic components when you blow them

up:-)

> >
> > Regards, Terry
> >
> >
>