Re: Simple PSU stuff

Ok , I grasp precisely what you are saying about a gecko bipolar chopper driver and the theory but the original question only said bipolar and nothing about chopper drive. Despite that chopper drives seem to be the most preferred by members of this list there are still people using other current control methods. Indeed within the past week or so there was a machine that has just reached running stage using ucn5804's.

So perhaps there are 2 correct answers to the original question, depending on the specific driver to be used.

What do you think?

BTW smoothing or filtering have identical meanings in Australia, or did when I did my training many moons ago.

Regards
Bob Thomas

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis <mariss92705@y...>" <mariss92705@y...> wrote:
> Jan,
>
> Couldn't have said it better. Your'e hired; can you start Monday?
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, JanRwl@A... wrote:
> > In a message dated 12/13/2002 5:52:38 AM Central Standard Time,
> > echnidna@y... writes:
> >
> >
> > > Assuming each motor may operate simultaneously, the transformer
> for your
> > > power supply is not large enough to handle 3 - 2 amp bipolar
> motors.
> >
> > Bob:
> >
> > I thought this way, too, when I first bench-tested my first (only,
> so far)
> > bipolar-CHOPPER Gecko-drives (G210). Mariss explained to me why
> the MAGIC I
> > observed: I had about 30 Volts, unregulated but filtered
> ("smoothed" in
> > English-English; We Yanks call that "filtered"), DC feeding two
> G210's,
> > those driving two 3+ amp motors, with two 3+ volt windings, each,
> i.e., about
> > 20 watts per motor. With BOTH motors stepping simultaneously,
> meaning that
> > neither was drawing only 1/3 current "at standstill" like the Gecko
> drives do
> > after a second or so pause, the DC from the 30 V supply was less
> than two
> > amps! Yet, both motors had "full rated torque". Mariss pointed
> out that the
> > supply was supplying WATTS, as the chopper-drive still puts-out
> about 30
> > volts with this supply to the motor-windings, but "chopped", to
> average the
> > current down to the 3+ amps rating.
> >
> > If I dare attempt "the math": Say the supply IS exactly 30 VDC,
> and the
> > current-rating per winding for the motor in question is exactly 3.0
> amps, and
> > the rated winding voltage is exactly 3.333 volts. I.e., exactly 10
> watts per
> > winding, or 20 watts for this motor. Now, to keep only 20
> watts "into" the
> > motor with a 30 VDC supply, we must "chop" the voltage/current to
> maintain 20
> > watts total to the motor, so, with 20 W./30 V. = 0.67 amp, less
> than ONE
> > winding's rated current! Yet, it "appears" that 3 amps is flowing
> in BOTH
> > windings (and it is!). It's the WATTS, not the apparent total
> current, as
> > the VOLTAGE is much higher than the 'rated" voltage (which would be
> 3.333 V.
> > at rest).
> >
> > Yep, it took me a few minutes and some pencil-scratching to "get
> this", but
> > it is now (nearly) clear in MY feeble mind!
> >
> > HOPE this clarifies for you! (Mariss: Did I get it
> right???)
> > Jan Rowland
> >
> >
> > [Non-text portions of this message have been removed]