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

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