Re: Stepper current - how bad is underdriving a motor?

Jeff -

As Mariss keeps telling us, derating by 71.5% is not a great idea with
microstepping, as you tend to get bunching of the microsteps. So half the
current is probably the right answer here.

Regards,
Tony

At 07:52 23/12/2002 +0000, you wrote:

>Hello John,
> If the motors are rated at 15.2 Amps UNIPOLAR, then if you use
>them in full-coil BIPOLAR series mode, I beleive you want to derate
>them to 71.5% of the UNIPOLAR rating, not half. This comes to 10.87
>amps/phase. 7 amps/10.87 gives a 64% of maximum total torque
>rating. I would double check this (my evaluation) and get another
>opinion though.
>
>Jeff
>
>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "jmkasunich
><jmkasunich@y...>" <jmkasunich@y...> wrote:
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Tony Jeffree <tony@j...>
> > wrote:
> > > At 12:18 21/12/2002 +0000, you wrote:
> > > >I just acquired a NEMA42 stepper,
> > > >
> > > >840 oz-in,
> > > >1.45V
> > > >15.2amps !!
> > > >
> > > >I was wondering how much torque I
> > > >sould expect out of it when running
> > > >on a Gecko at 7A? I do know that
> > > >whatever torque I get will stay
> > > >there to a rather high speed, thanks
> > > >to the very low voltage.
> > >
> > > You would expect to get approx 1/2 the torque at low
> > > speeds, but as you say, the low voltage gives plenty
> > > of headroom to get good performance at high speeds.
> > >
> > > You haven't said whether the motor is 4, 6, or 8 wire.
> > > If it is 6 or 8 wire, the alternative is to use it in
> > > full coil (6-wire) or series connected (8-wire) at 7A;
> > > you should then get close to the rated torque at low
> > > speeds.
> > >
> > >
> > > Regards,
> > > Tony
> >
> > Duh! Why didn't I think of that! It is six wire. So
> > full coil turns it into a 2.90V, 7.6A motor. That's
> > almost perfect. With a 48V supply, I'll have 16.5x
> > voltage, so I should get good high speed performance,
> > and 7A into a 7.6A motor will deliver nearly full
> > torque. Thanks Tony!
> >
> > John Kasunich

Regards,
Tony