Fractional AC motor question

Discussion in 'General Electronics Chat' started by batboy, Aug 29, 2009.

  1. batboy

    Thread Starter New Member

    Aug 28, 2009
    My son has a shredded with forward/reverse, paper sensing and the normal safety features. The circuit board quit so he asked it I could wire just the motor to a switch. Sounded easy, but..... I can certainly do what he asked, but it appears reversing the motor should be possible. The existing circuit board switch is a DPDT break before make which reverses the power connections through the windings. However, I do not understand why, in an AC motor, this reverses the motor direction.

    I have attached a sketch of the setup. I have shown the two states, forward and reverse, rather than include the switch which complicates the diagram too much.

    Would appreciate any comments.
  2. mik3

    Senior Member

    Feb 4, 2008
    In your drawing the wires are on the same sides of the motor both in forward and reverse.

    Are you sure the motor is AC?

    How many wires are coming out of the motor?
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    It looks like a typical 'universal' motor, they run on AC or DC.

    To reverse it, you need to swap the connections to the armature/brushes relative to the field windings.

    (Or, equally, swap the field winding connections without changing the brush connections).

    The direction is controlled by the *relative* polarity of the armature to the field. When both swap together, as with AC, the running direction stays the same.

    Swap either on it's own (so relative to the other) and the direction reverses.
  4. batboy

    Thread Starter New Member

    Aug 28, 2009
    There are four wires coming from the motor; two from the field and two from the brushes. The wires all went to the shredder circuit board. The diagrams were my interpertation following the foil on the circuit board, except of course I could not trace the logic through the IC's on the board. I plan to disconnect totally from the board and just use the existing switch. Reversal is not necessary but looked 'doable' from what I could tell, just don't quite know how. The motor is definitely AC.