08-02-2014, 11:08 PM
The speed of an an AC motor is set by the frequency of the supply and the number of pairs of poles.
With DC motors, which is what this basically is, the input voltage effects the speed but it's also determined by the relative strengths of the Armature and Yoke magnetic fields: the stronger the armature field the quicker it goes.
Where a variable control is required it's more practical to strengthen or weaken the field as this has less of an effect on the torque. A rheostat is fitted in parallel with it to divert the some of the current.
Interesting to note that the plate says "Rotor A" though.
Motors with brushes that operate on AC mains are strictly speaking Universal ones which will run on AC or DC. The difference between these and DC only ones is that the armatures and pole pieces are made from laminations to prevent eddy currents - for DC only use they could be solid.
The fact that the supply polarity is changing fifty times a second doesn't matter to the direction of rotation as to change that the connections to EITHER the Yoke or Armature have to be reversed, not both.
I'm surprised just how much of this guff I can remember.
- Joe
With DC motors, which is what this basically is, the input voltage effects the speed but it's also determined by the relative strengths of the Armature and Yoke magnetic fields: the stronger the armature field the quicker it goes.
Where a variable control is required it's more practical to strengthen or weaken the field as this has less of an effect on the torque. A rheostat is fitted in parallel with it to divert the some of the current.
Interesting to note that the plate says "Rotor A" though.
Motors with brushes that operate on AC mains are strictly speaking Universal ones which will run on AC or DC. The difference between these and DC only ones is that the armatures and pole pieces are made from laminations to prevent eddy currents - for DC only use they could be solid.
The fact that the supply polarity is changing fifty times a second doesn't matter to the direction of rotation as to change that the connections to EITHER the Yoke or Armature have to be reversed, not both.
I'm surprised just how much of this guff I can remember.
- Joe
