Re: Stepper de-rating

Mechanical power output is proportional to the supply voltage
while "iron losses" increase with the square of that voltage. The
ultimate limit for power supply voltage is the motor case
temperature, empirically at 20 - 25 times the motor's rated voltage
(V = phase amps * winding resistance).

If your speed requirement is low, use a low supply voltage and have a
cool motor.

Mariss

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