Series Connected D.C Motor Characteristics

[1988ajk]

Hi all,

Please excuse me for such a simple question, I am a predominantly a mechanical engineer.

Does a series connected D.C Motor have a linear speed/torque relationship or a curve?

I am aware that both have speed (RPM) decreasing as torque (Nm) increases.

Many thanks in advance!

[KingNothing]

It is 'mostly' linear, but there are some nonlinear artifacts in a real motor.

http://lancet.mit.edu/motors/motors3.html#tscurve

[orthogonal18]

No, the torque-speed curve will not be a linearly decreasing. It will be hyperbolic in shape. This is due to the armature winding and field windings being connected in series.

http://www.engineersedge.com/motors/dc_series_wound_motor.htm

[1988ajk]

Many thanks,

the last post has cleared up some ambiguous notes I have.

[FOIWATER]

Since your series field is in series with your armature, and has a very low resistance, about .4 ohms... it saturates very quickly providing maximum flux on relatively low provided current. For that reason, the motor has Amazing starting torque, but since the winding is saturated early it produces less and less torque as armature current is applied form no load to full load.

In summary, the motor has excellent torque on starting, but has poor speed regulation from no load to full load (as armature current is applied)

[1988ajk]

say if the d.c motor were a permanent magnet type, would this have the same characteristics?

I presume that they would stay the same, as the magnets do the same 'job' as windings.