Re: [CAD_CAM_EDM_DRO] Voltage, Current, Resistance and Heat?

At 23:39 08/11/2004, you wrote:

> > Recently, I changed out that driver board for the Hobby CNC driver
> > board which is a chopper driver. I set this unit up at 1/4 step and
> > it runs very smooth and I could achieve higher RPMS which is cool.
> > But, in playing around with it for the last 2 days, I noticed
> > another COOL thing, the motors barely get warm to the touch - they
> > run very cool.
> >
> > After some tuning, I believe I have the torque pretty close on the
> > new board as the old board. But still, the motors run cooler.
> >
> > This got me to thinking about something I read somewhere.
> >
> > "Torque is directly related to current"
> >
> > If this is the case, then, if I have the same current I should have
> > the same torque. Also, I believe the motors should run at the same
> > temperature.
> >
> > So, I am wondering if I could run more current (Amps) into these
> > motors than what is given on the spec sheet. Eventually, I will be
> > running them at about 40 volts when I get the parts for the new
> > power supply. But, I am VERY tempted to crank up the current to see
> > if I can get more umph out of them. Now I know I am not suppose to
> > do that, but if the motors are running cool, I am wondering if I
> > would in fact hurt them by running up the current while keeping a
> > very close eye on motor temps.
> >
> > Any thoughts on this?
>
>Many controllers reduce the current when the stepper motor is idle for a
>while. That is enough to act as a brake. Full current is applied when
>motion is required. The reduced current reduces heat loss and power
>requirements.
>
>Try running the X stage back and forth at full velocity for 30 minutes.
>If the stepper gets hotter then they are reducing current when idle.
>
>In general, I would stay within stepper manufacturer and driver
>manufacturer recommendations.

Driven in full step by the old L/R drive, with both windings always on, the
motor is always consuming a total of twice the amps-per-phase rating.
Driven in 1/4 step by a microstepping driver, the maximum current that the
motor will be sinking is root-2 times the amps-per-phase rating in both of
the windings, i.e., 1.41 times the nameplate current rating. So, regardless
of any reduced current settings when idling, the motors will run hotter
driven full step by the old L/R drive, because it is always sinking around
50% more current than with the microstepping driver.


Regards,
Tony