Re: Stepper de-rating

Mariss:

Thanks, does this mean that if I want to use steppers I should expect
an 80 deg. C operating temperature even with a good drive like the
G201. I understand eddy currents and iron losses but I guess I did not
realize they were that large. Is this true if you turn off drive
current after a motion. My application only calls for motion at less
than 10% duty cycle and the lead screws cannot move the stepper when
it is off.

The only reason I thought about steppers in the first place is that I
want to keep the handwheels and their micrometer dials. None of these
problems exist with servo motors but they are geared down and hard to
turn manually.

Ken


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
<mariss92705@y...> wrote:

> 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