Re: Members

Peter,

The problem is not the transformer but rather how and when you would
switch between the taps.

The how:

You would have to use some type of power semiconductor to do the
switching, probably a triac since AC is involved. Three taps, three
triacs. Add failsafe triggering circuitry to insure only one triac is
on at a time. Gets complex since 2 or all triacs on simultaneously
would be destructive.

Or you could design a buck-type switching regulator to cover all
voltages between 0 and maximum. Not a trivial task either.

The when:

What determines when do you change the voltage? Probably at certain
step frequency thresholds. That requires a frequency to voltage
converter.

Or you could sense when the drive begins to stop chopping to increase
the voltage.

So what is the payoff for all this expensive trouble? At high speeds
your motor would need a high voltage and it would get very hot. No
improvement there. At low speeds it would be cooler, but if you run
at low speeds, why not just use a low supply voltage?

There are drive switching topologies that accomplish directly,
primarily variations of the regenerative type. This type effectively
makes the motor "see" a low voltage at low speeds, then switches to
non-regenerative at high speeds. My experience has been they
sacrifice low speed smoothness so I have rejected that approach.

Mariss

--- In CAD_CAM_EDM_DRO@y..., cadcamcenter@y... wrote:
> mariss92705@y... wrote:
>
> > In theory a variable voltage supply might reduce motor heating
but
> > the slight advantage is simply not worth the considerable circuit
> > complexity.
>
> If a multi-taps transformer is available/easily made to order, is
the
> additional switch too much trouble for this little extra advantage -

> higher voltage to drive the current into the motor easily, but with
> the option of switching to a lower voltage, therefore cooler
running
> motors when one expect only low steps/sec.?
>
> Peter