olin_piclist@embedinc.com (Olin Lathrop) wrote:
> Gerhard Fiedler wrote:
> > 0 torque at the shaft at max. speed (when all the power is used
> > to overcome internal friction and other losses)?
> 
> Only indirectly. Even if the motor was ideal and had no friction and
> zero loss, you would still have 0 torque at the unloaded shaft speed.
> The unloaded shaft speed is the limit where the voltage applied to the
> motor is cancelled by the back EMF of the motor acting like a generator.
> In reality that back EMF is a little less than the applied voltage, with
> the remainder times the current going to the various power losses such
> as friction and winding resistance.

Even that depends on the motor design. AIUI, a series-wound motor (works
on AC or DC), given unlimited current, will accelerate until it destroys
itself. These are the motors used, for example, in vaccuum cleaners. They
go as fast as the air resistance in the blower mechanism allows, and run
even faster whenever the air pressure is reduced (inlet blocked).

-- Dave Tweed
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist