Re: Power needed to drive 3 nema 42 motors?

--- In CAD_CAM_EDM_DRO@y..., "Raymond Heckert" <jnr@a...> wrote:

> See my ******* comment ******* below
> RayHex
>
> ----------
> > From: caudlet <tom@t...>
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> You can even take a secondary winding and
> > put it in series with a primary winding and use it to lower the

high

> > current secondary.
>
> ******* THIS THEN BECOMES AN AUTOFORMER! *******

If you take any two windings on a transformer and wire them in series
and induce an AC voltage across them then any OTHER winding on the
transformer will output a ratio based on the total volt-turns of the
primary. The suggestion was based on a transformer with multiple
windings (>2). You do not loose isolation if the secondary winding
is not physically connected to any of the primary windings.
Transformers are designed as a group of windings each with a
beginning and end (sometimes tapped at various points)placed on an
insulated bobbin (conventional E-core transformers) and within the
presence of a magnetic material. There are specific formulas that
determine the amount of voltage that can be impressed on a given
winding before the magnetic core of the transformer passes into
saturation. This formula has the normal sustainable magnetic field
below satutation in Gauss, along with the applied voltage, the number
of turns, etc. What that means is that any windings in the field can
be treated as part of the unit and used as long as you maintain the
core below saturation. Note that current is not part of the turns
ratio consideration and only comes into consideration when wire size
is calculated. Wire size then determines how big your bobbin has to
be to hold all the windings and that usually drives the size of the
core. While there are other factors like air gaps, eddy currents,
and such they only start to be significant at higher frequencies
(KHZ).

As long as you stay within the volt-turns constant you can put
windings in series (boost or buck mode) and add or subtract
voltages. Lets say you have a transformer with a 120V single primary
winding and a 12, a 24 and a 36CT set of windings. If we apply 120AC
across the primary we could get individual isolated (from each other
AND the primary) voltages of 12,24 and 36 (or 18 at the CT). Now you
can series any of the secondaries to get all kinds of voltages (36,
72,30,54,etc) The only limitation is that because of wire size you
can only draw the amount of current of the lowest current winding.

Conversely you can place 12VAC on the 12V winding and get 120V AC OUT
of the primary (and so forth) Let's say you take the 24V winding and
put it in series with the designated primary and impose 120VAC AC
across the two end points. You have effectively increased the number
of turns in the primary so the ratios to the other secondaries change
by the same amount. I am not going to go through all of the math or
examples. I will not go into out of phase (bucking) two windings but
you get the idea. The more windings you have the more possible
combinations you have. All of these presume you use a seperate
isolated winding(s) as your final output.