Re: Stepper de-rating

Depends entirely on the drive type and if you are microstepping or
not. Resistive heating (I^2*R) is only a part of it. The other heat
cause is iron losses (eddy current and hysterisis) which are
independent of the set phase current.

Chuck a stepper in a drill press, wires unconnected, and see if you
can touch the motor after spinning it for 5 minutes. The heat is due
to iron losses.

Good microstep performance requires running the motor at its rated
current. Less than rated operation leads to unpleasant interactions
between the switching freq and step freq at high speeds (instability).

Step motors are designed to run hot. The case temp is rated at 85C
for most motors.

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "bull2003winkle"
<bull2003winkle@y...> wrote:

> I hope this is not off topic, tell me if it is.
>
> I am wondering if all the stepper experts can advise and old servo
> motor guy about the merits and problems of derating a stepper. I
> understand why steppers dissipate power, there is always current

flowing.

>
> What would happen if one were to size a stepper at twice what the

load

> needed and ran it at half rated current. It seems it would have to
> operate at a much lower temperature. If the increased rotational
> inerita were not a problem, what else might be.
>
> Thanks;
>
> Ken