AC motor rotation is backwards

Discussion in 'General Electronics Chat' started by Gdrumm, Jul 10, 2010.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    I picked up a discarded shop vac, and found that one of the brushes was broken. I had a similar brush in my collection, and replaced the bad one.
    The motor worked fine, but when I assembed the shop vac and tried it, it is blowing, not sucking.

    I disassembled it and made sure that I haden't done something in reverse with the impeller, etc.

    I've searched the web, and can't understand some of what I'm reading about AC motor rotation.

    What am I missing?

    Is my jury rigged brush the problem?

  2. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    Never mind, I'm a dummie....
    Once I completely reassembled the entire vacuum, I realized that the nozzle which was blowing and not sucking (which looked like the place where the hose would attach) is actually the exhaust.

    I'm still curious however, what determines the direction of rotation on a motor for a device such as this? Is it in "the windings"

    Thanks, Gary
  3. Markd77

    Senior Member

    Sep 7, 2009
    There is a bunch of info on wikipedia on AC motors. Some of them have a ratchet so if they start in the wrong direction they bounce back.
  4. debjit625

    Well-Known Member

    Apr 17, 2010
    May I have not understood it correctly but if its a poly phase motor,then you have connected the capacitor in wrong way.
    How to connnect ,their are two coils 90 degree apart from each other and they are connected in series now we connect the capacitor in parallel with these two coil and provide power to one of the coil this coil will have a bit less winding fron the other.

    Google about poly phase motor
    Good Luck
  5. eblc1388

    Senior Member

    Nov 28, 2008
    A polyphase motor with *brush* and capacitor?

    The motor in our OP post is a type of universal motor. Just google "Universal motor" for more information.

    The rotation of this type of motor depends on the relative direction of current flowing in both the armature and field coil, which usually are connected in series. Reverse the electrical connection of either one will change the direction of rotation.

    A bit of warning though. The brush neutral axis is usually shifted for one particular rotation direction to counter the effect of armature reaction. The motor if reconfigured to rotate in the counter direction would suffer extensive sparking from the brushes.
  6. BMorse

    Senior Member

    Sep 26, 2009

    The op had the hose connected to the exhaust, that is why it was blowing.... he had corrected that already so it has nothing to do with caps or wiring....

    B. Morse