Re: simple stepper power question.

Tony,

Yes, and I bet the L298 got even hotter! This method depends on a
very efficient drive to work, where the drive's contribution can be
neglected. Otherwise a refinement is necessary to eliminate the
drive's contribution to the total power change. Here's how to do that.

Use a pair of ferrite-core inductors in the place of the motor. I use
two 600uH, 7A rated chokes. You can find these under the heading
of "hash chokes" in the Digikey catalog.

These chokes have very small losses (<1W) and can be used to simulate
a step motor on the test drive. This means all losses will be in the
drive.

Run your drive with these chokes and graph the power supply Watts
into the drive from 0 amps/phase to maximum amps/phase.

Subtract this wattage from your no-load (zero torque) to full load
(stall torque) power supply wattage readings. The result will be an
accurate reading of the power absorbed by the motor.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "tonyjeffree" <tony@j...> wrote:
> Mariss -
>
> Tried your procedure yesterday evening on a small motor of unknown
> power (other than it was marked 1.1A/phase 4V, 6-wire motor) and a
> 25V supply, driven via L297/298.
>
> Measurements using 1/2 and full coil at rated amps yielded
reasonably
> sensible numbers - the motor looks to be about 60 oz-in. Just to
see
> what would happen, I upped the L297 current setting to 2 amps and
re-
> measured, still on full coil. (Yes, I know - the motor *did* get
> warm <g>). The measured supply current under load actually
*reduced*
> relative to the supply no-load current under these conditions.
>
> Any theories?
>
> Regards,
> Tony
>
> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> > Dave,
> >
> > Yes there is. All you need is a multimeter and a calculator. Do
the
> > following:
> >
> > (1) Measure your DC voltage accurately
> > (2) Set the meter to DC Amps
> > (3) Put it in series with the power supply to the drive
> > (4) Run the motor at a known speed (greater than 1 rev / sec)
> > (5) Measure the power supply current at no load on the motor
> > (6) Now the tricky part. Load the motor down and note the current
> at
> > the moment the motor stalls. This may have to be repeated several
> > times to get an accurate reading.
> > (7) Take the difference between the no-load current and the stall
> > current. Multiply the result by your power supply voltage. The
> > product will be the motor output power in Watts mechanical.
> > (8) The torque at that speed will be: oz-in = Watts * 4506 / full
> > steps per second
> >
> > Mariss
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "dave_ace_me" <davemucha@j...> wrote:
> > > is there a formula to determine power of a stepper ?
> > >
> > > I have a Slo-Syn NEMA 34, 1.7 volt, 4.5 amp
> > > single stack.
> > >
> > >
> > > Also, has anyone put together a simple test
> > > for stepper power ? Seems like a weight,
> > > and a long crank arm with holes drilled
> > > each inch would allow one to keep moving
> > > the wieght farther out until the motor
> > > started missing steps.
> > >
> > > Dave