olin_piclist@embedinc.com (Olin Lathrop) wrote:
> Dave Tweed wrote:
> > 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.
> 
> Yes, if *current* is held contant. Torque is current minus any viscous
> friction. I was talking about holding voltage constant.

So was I. Constant voltage, unlimited current. I don't recall the details,
but "back EMF" never fully opposes the applied voltage in a series-wound
motor.

Actually, according to one website (http://www.gizmology.net/motors.htm):

   In a series-wound motor, the field current is always equal to the
   armature current. Under no load, the torque produced by the motor
   results in acceleration. As speed increases, induced voltage would
   normally increase until at some speed it equalled the applied voltage,
   resulting in no effective voltage, no armature current, and no further
   acceleration; in this case, however, increasing speed decreases field
   current and strength, stabilizing induced voltage. Torque never drops
   to zero, so the motor continues to accelerate until it self-destructs.

So, unlimited current is not a requirement!

-- Dave Tweed
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