Re: [CAD_CAM_EDM_DRO] Stepper Motor Torque vs. Wiring

Bipolar and unipolar refer to how the drive electronics energize the coils.
When you use a unipolar scheme (current flow is always in the same direction
from the coil ends to the center tap) to drive the motor you are pretty well
describing how the coils will be connected at the same time. But, when you
use a bipolar scheme (current flow reverses direction) you have a number of
ways to connect the coils. So, you are confusing yourself by thinking that
the coil connection is what makes it bipolar or unipolar.

I don't think that Mariss is saying you will get double the power with a
bipolar drive compared to a unipolar. The normal figure for torque
difference between them is 30% difference. Looking at the spec on a Pac Sci
Powermax II I have handy they give a unipolar rating of 151 in/oz and a
bipolar of 214 in/oz. There is no difference for all practical purposes in
the holding torque between a bipolar series (full coil), half coil, or
parallel connection. Where the difference comes in is the rate at which the
running torque drops off. Series will run out of steam the fastest.
According to Mariss the difference between parallel and half coil is so
small it is meaningless.

Tim
[Denver CO]

----- Original Message -----
> Hi all,
>
> I was hoping somebody could enlighten me. Just when I think I'm
> starting to understand something, I read something that confuses me
> again....
>
> The following link shows a chart of the torques, etc of some Superior
> Electric Stepper Motors.
>
> http://www.slosyn.com/ssstepmotors_stndrdnema34.html
>
> I have some M092-FD09 motors that I'm in the process of connecting.
> Last night I hooked them up in 'Full Winding' mode according to
> Mariss' explanation in the Geckodrive papaers. My understanding was
> that the full winding mode corresponds to what Superior Electric is
> referring to as 'Bipolar' in the above webpage and that the half
> winding configuration is what is referred to as unipolar. (My primary
> indication of this is that the inductance on the bipoar section of
> the table is 4X that in the unipolar section which corresponds to the
> statement made in the gecko papers if I'm not mistaken).
>
> However, two questions come up.
>
> 1st, The Geockodrive instructions indidcate that the current should
> be limited to half of the unipolar nameplate rating on the motor but
> the Slo-Syn says that the current for bipolar is not quite 1/2 the
> amount. Is 1/2 the current a conservative theoretical number and the
> slo-syn chart is likely giving a more accurate empirical value for
> those windings?
>
> 2nd (and most confusing), the geockodrive instructions indicate that
> a motor connected in parallel (or half winding, since a series
> connection is associated with a full winding connection) will have
> twice the power of a motor connected in series (or full winding).
> This directly conflicts with the information on the above website if
> bipolar refers to full winding and unipolar refers to half winding.
>
> Please help! :-)
>
> Thanks,
> -Chris
>
>
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