RE: [CAD_CAM_EDM_DRO] Re: COMPLETE 3 axis CNC electronics package (plug-n-cut, ready to go)

HI Mariss,

> >
> >(sip)
> >
> > Windings in parallel are said to have the best speed. But only
> >slightly better then just using 1/2 the winding.
>
> Yes they are. In fact twice as good.

This is what I was trying to say (quote from your "stepper basics" white
paper):

"Eight-wire motors are about 3% more efficient when parallel connected then
an equivalent half-winding connected six-wire motor..."

I consider 3% "slightly better", and not worth the effort!

> Inductance increases as the square of wire turns (mutual inductance)
> so a full winding has 4 times the inductance of a half winding.
>
> Motor power output is proportional to Vs / SQRT L . A half-winding
> motor produces twice the power of a full-winding motor for the same
> power supply voltage. You'd need to double the power supply voltage
> (Vs) on a full-winding motor to recover the loss in performance.
>
>
> > It seems to me that it would be good to use the entire winding >
> (other considerations aside), because the heat dissipated would be
> >better distributed. But not at the cost of slower speed!
>
> Center-tapped motor windings are bi-filar, making them thermally
> intimate. It makes no difference thermally to use a half-winding 100%
> of the (bipolar drive) versus both windings 50% of the time
> (unipolar).

That makes sense.

>
> > I have seen a better fit for a stepper (current wise) by using the
> >full winding, sometimes 1/2 the current can allow you to use a
> >smaller driver if ultimate speed is not needed. It's good to have
> >choices!
>
> Always use 1/2 rated current for a full winding! The motor is an iron-
> core inductor; full current thru a full winding results in magnetic
> saturation and a percipitous drop in inductance. This can kill a
> switching drive which relies on inductance to operate properly.
>
> Secondarily, full current thru both half-windings doubles I^2 * R
> losses,(twice the heat).
>
> Mariss
> >

Yes, that's what I meant when I said "1/2 the current can allow...".
Instead of needing say 4A for a 1/2 winding, one can use 2A and the whole
winding. Again, won't run as fast! Full current through the whole winding
usually results in the magic smoke getting out of the stepper, if not also
the driver!

Alan KM6VV