Re: [CAD_CAM_EDM_DRO] Re: Stepper de-rating

I hope you don't mind my interjecting here a bit, but one does have to
be aware of the potential operating temperatures of steppers and
brushless DC moters for that matter. Some of these motors are designed
to run extremely hot and can result in very bad burns if touched at the
wrong time. So care should be taken with any stepper that has
recently been running.

The thermal issues may also cause you mechanical issues. It is a good
idea to make sure that the stepper mounting does not transmit thermal
energy to the bearings or lead screws.

Thanks
Dave


bull2003winkle wrote:

>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
>>
>>
>
>
>