Re: [CAD_CAM_EDM_DRO] Re: Members

mariss92705@... wrote:

> Hi,
>
> Actually a variable voltage is more for the motor's benefit than
> anything else.
>
> Step motor heating has two sources, one obvious, one not.
>
> The obvious one is the heat generated anytime current passes thru a
> resistance. The resistance here is the motor winding, and automatic
> standby current schemes are used to reduce this heating when the
> motor is stopped.
>
> The other heating source is "iron losses" (eddy current and
> hysterisis). You can think of it as a "friction" in the iron as the
> magnetic dipoles switch back and forth. This heat quadruples when
> voltage doubles.
>
> A fun way of proving this exists is to chuck-up a step motor in a
> drill press. Set it to high speed and make sure the motor leads are
> not touching each other. The motor will be too hot to touch in about
> five minutes, yet no current was flowing in the windings!

Interesting experiment. But, I think, if you analyze the conditions,
that this is actually WORSE than normal operation. In normal, electrically-

driven stepper systems, the winding currents are driving the stator
field, which then moves the rotor in sync with those fields. The
actual hysteresis in the stator iron may be much less in this case
than in your special-case test. I will note that my Vexta motor and
driver get quite warm when running at high speed, but stay cool when
running at low speed. I don't know if they do anything fancy with respect
to motor current or voltage at higher speeds, but I don't think so.

Jon