Re: 8-wire stepper: series is 1/2 the amps.Strange but True

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Harvey White <madyn@i...>
wrote:

> On Sat, 31 May 2003 20:24:53 -0000, you wrote:
>
> >
> >Hi Lee,
> > Won't series winding (full winding) RESISTANCE be TWICE the

amount

> >of the single coil (1/2 coil), while your series winding

INDUCTANCE

> >be FOUR times that of the single coil (1/2 coil)?
> >
> > With series winding (full winding), you have twice the number of
> >turns of wire being energized as half winding, so you use half the
> >amount of current to acheive the same holding torque.
>
> Seems to be two factors here. One is the maximum flux through the
> motor, the other is the power dissipation of the motor. The
> inductance does relate to the maximum supply voltage needed

for "good"

> performance.
>
> The motor is not rated (unless it's stated by the manufacturer) for
> both halves of a 6 wire motor actuated at once (running unipolar as
> bipolar). You have to derate the motor to get this to keep both the
> flux (excessive can demagnetize the motor) and the power dissipation
> in limits.)
>
> So running both halves of the motor windings (say 4 volts at 2 amps

if

> unipolar) as bipolar, full coil means that you have an 8 volt

winding,

> but at about 1.3 amps, assuming a derating factor of 0.66. Using

one

> coil of a unipolar stepper (ignoring the lead completely, using only
> the CT and one wire) will get you the original nameplate ratings..

say

> that same 4 volts at 2 amps. You will need a bipolar driver to

handle

> it, and the easiest one of those is a chopper style driver...
>
> Further complications come when you use 8 wire steppers, which are
> steppers with all 4 coils wired independently.
>
> (All the above is what I've managed to piece together, if it's
> incorrect, please correct it, and blame it on the lateness of the
> hour...)
>
> Harvey

The thing that gets cloudy for me is that a 4 wire stepper has a
single coil on a circuit. an 8 wire can be wired for single coil and
just not using the remining two coils.

yet a 6 wire is an 8 wire with a single center tap that connects 2
coils. and all other things being equal, that style is often
referred to as having one coil and being wired as half-coil.

As I have read, series will deliver full torque up to exaclty half
speed of a single coil (on an 8 wire, or half-coil on a 6 wire)

I am using series and using 1/2 nameplate as the setting for my
Gecko's.

so, the question how does one determine where the torque starts to
drop off when on is not using a single coil (on an 8 wire) but is
using less than nameplate on a series wired motor ?

Dave

>
>
> >
> >Jeff
> >http://www.xylotex.com
> >