8 wire half or Serial ? ( was Speed - Parallel vs serial ( was Re: Motor

Dave,

On the series / parallel thing. Here is the reason series needs half
the current of a parallel connection.

Torque is equal to current multiplied by the number of turns of wire
it passes thru. This is called "ampere-turns" naturally.

In series, current passes thru twice as many turns of wire than it
does in parallel, so only 1/2 the current is needed for the same
torque.

Some might think "why not keep the current the same and get twice as
much torque?". The reason why not is because of magnetic saturation.

You can think of iron being composed of countless microscopic bar-
magnets, all randomly oriented. These "magnets" are called "magnetic
dipoles" Because of their random orientation, iron has no net
magnetism.

When you wind a coil around iron and pass current thru it, some of
these magnetic dipoles align with the coil-generated magnetic field,
strenghtening it. When you double the current, twice as many dipoles
align. At some threshold current though, all the dipoles are aligned.
This is called "magnetic saturation". Any further increase in current
cannot increase the magnetic field.

Step motors are designed to operate at about 80% of magnetic
saturation when rated current is passed thru its windings. To keep it
at that point, half the rated current must be used if the number of
wire turns is doubled (series or full-winding operation).

Mariss

--- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...> wrote:
> Hi Peter and all,
>
> It seems that half coil offers a simple solution and would let me
run
> straight away.
>
> Now my ignorance will become abundantly clear.
>
> using 2 coils, like a 6 wire stepper, center connected, one end un-
> used, would use nameplate amps.
>
> getting the correct pairs and matching them and wiring up each pair
> as if it were one coil (again like an center connected 6 wire
> (parallel)but now using the 'other' end wire/circuit) would use
> nameplate amps.
>
> finding the correct 2 pairs and series wiring would use half
> nameplate, and run half as fast. Like an end connected 6 wire.
>
> Miswiring which pairs (not shorting out wires or other mistakes)
> would only make the motor miss.
>
> The idea of powering two sets of coils in series with half current
> has't integrated itself in my thinking as yet. Seems two series
> lightbulbs at full voltage would burn half as bright, but if the
> voltage were halved they would be really dim. My thinking is that
> I 'want' to double the power at series. I am intelegent enough to
> follow the directions and use half current.
>
> Dave
>
>
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "cadcamcenter" <cadcamcenter@y...>
wrote:
> > > I did that first. an 8 wire stepper uses 2 sets (pairs) of
> coils,
> > it
> > > does not go into how to decide which two pairs to connect.
> > >
> > > Dave
> >
> > This question occurs quite frequently. Let's see how one can
> > approach. The combined wisdom of this list says best is to wire
in
> > half-coil.
> >
> > 8 wires stepper are 4 coils terminated at both end with separate
> > wires, forming 4 pairs of wires. With a multimeter, it will be
easy
> > to find these 4 pairs. Let's call them A, A' and B, B'.
> >
> > Wiring in half coil mean that 2 of these 4 pairs will be
connected
> to
> > the driver, leaving the other two open. This mean there are only
4
> > possibilities and they are:
> >
> > A and A' no good
> > B and B' no good.
> > A and B good
> > B and A' good
> >
> > The question is, what happen when you connect A and A' and B and
> B'?
> > I guess the motor will not turn, but no harm will be done to the
> > driver/motor provided voltage, current setting are within
> permissible
> > limits. (hope the experts will elaborate on this)
> >
> > When wired in the other 2 (good) possibilities, the motor will
> turn,
> > only thing is, if polarity is wrong, motor will turn opposite to
> > intended sense. A simple remedy will be to reverse the pair
> > connection or reconfigure the controller.
> >
> > In any case, I believe the way to approach this is
> >
> > 1. determine the paired wires with multimeter
> > 2. pick any 2 pairs, connect them to the driver.
> > 3. Test. If wrong pair motor will not turn, probably make noise,
> but
> > no harm done. (experts please correct if wrong)
> > 4. Make a note, pick another 2 pairs.
> > 5. At most, you need only 3 trials before you get the motor
> turning,
> > and at most 4 to get them turning correctly.
> >
> > Hope I did not give inaccurate info. (disclaimers apply)
> >
> > Peter
> >
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...>
> wrote:
> > > <snip>
> > >
> > > >
> > > > For wiring 8 wire stepper motors, go to www.geckodrive.com
and
> > look
> > > at their
> > > > white paper on stepper motors.
> > >