stepper voltage ( was Re: Simple PSU stuff

--- 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]