Re: Re: Power Supply

Actually, Larry has it more correctly in this situation, with qualifiers.

Heat will demag a rotor, but only if you get up around the curie
temperature. For Samarium cobalt magnets (very common rare earth magnet)
you need to be in the 700 degree F range. For Neodymium-iron-boron magnets
(higher strength but can't take the heat), you are in the 300 degree F
range. If your motors are getting that hot, you are seriously overdriving
them, or doing something that you shouldn't.

Excess current will demag a rotor as well. If you look at the B-H curve for
a SmCo or NdFeB magnet, at elevated temperature, the curve develops a
"knee". This means that if you have too high a current, the magnet actually
can be demagnetized. When the current is removed, the strength of the
magnet is permanently impaired. Usually what happens when you demag a rotor
this way is that the motor will run but at nowhere near the power you used
to get.

Gary

> > There is something I read that is very important to
> > the point of running stepper motors at current levels
> > above there rating.
> >
> > What I read says that every time the current level
> > exceeds the rated level it has the effect of
> > demagnitizing the motor,deterorating the torque that
> > the motor is capible of.
> >
> > I can't say that this is true for all motors or at
> > all, but I read it. If there is a magnet inside the
> > motor it makes sence.
> >
> > Larry Wright
>
>
> What damages the motor is heat. It is the I^2*R (the current
> squared times
> the motors winding resistance) heat dissipation (in watts) of
> the motor.
> This heating is at the highest when the motor is stalled. It
> is the HEAT
> that demags a motor. Some magnets are more heat resistant
> then others.
>
> Jeff Martin