Re: PWM vs Constant current

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:

>
> Jarrett & Heidi Johnson wrote:
>
> >Our (K142C) Constant Current Source systems sense the drop in

current and

> >increase the voltage to the motor and thus the current and power is
> >maintained with higher speeds. A common motor we tested gave

similar torque

> >at around 300 RPM as at 1 or 2 RPM (this is as FAST as we tested

with a 200

> >step motor).
> >
> >
> Oh, so 300 RPM is fast?

It probably is fast for that technology.

> I demoed a stepper system at the NAMES show in
> 2002,
> I think, using the Gecko 201A drive (a chopper or PWM design) where the
> motor was shoving the table of a 150-Lb mini-mill around at 90 IPM. At
> that speed, the motor was spinning at 1440 RPM! I would guess the
> motor was delivering close to 50% of rated torque at 1440 RPM.
> I was quite impressed by this performance, and I doubt anybody's
> drives can do much better. I probably could have gotten even better
> performance out of the same motors with with a higher power supply

voltage,

> but there was no need. These were not the latest high performance

motors,

> either, but some 30 year old ones salvaged from printers.
>
> Jon

Hey, didn't anyone ever tell you to play fair ?
Mariss had been in drive design for what, ? 20 years ?
the Gecko 201-revA ?, was his first unit.

you could match motors and power supplies and drive the driver with a
very uniform pulse stream. Do I remember correctly when the whole
G200x came out that he ran at 200,000 hz ? on a 10 microstep driver
that is 20,000 full steps per second. divide that by 200 steps per rev
to get 1,000 steps a second, and multiply that times 60 ?

I remember 200,000 hz, but am not sure if it was into a stepper or a
servo.

But, I do recall that 1,440 RPM for a NEMA23 is about where the power
starts to get too weak.

Dave