AC Motor Reversal

Discussion in 'The Projects Forum' started by kfife, Aug 12, 2009.

  1. kfife

    Thread Starter New Member

    Aug 12, 2009
    Preamble: I have some power tools with 110/220 single phase AC induction motors. Per documentation from the manufacturer, I have converted many of them to run on 220 (prevents voltage sags on start up inrush). You probably know the drill: 4 wires marked 1&2, 3&4 either wire them in series for 220 or in parallel for 110.

    Question: Have I got enough access to the motor internals to make it reverse? Are either of these pairs connected to the start windings? In other words, my understanding is that split-phase AC motors can be reversed by changing the polarity between the start and run windings. Could it really be as simple as reversing 1&2 or 3&4 to effectively change the inputs to the start windings downstream?

    If the answer is NO, because the start windings are connected down in the 'guts' of the motor in such a way as to disallow manipulation. How would one determine if a particular motor is 'presenting' the start windings so as to make it reversible? Is there a sure-fire way to identify the start windings? If the start capacitors are external to the motor, does that give me access to the start windings?

    The goal here is that I would like to be able to reverse some of my tools. (NOT my band saw for example, but YES to my disc sander). Any help would be much appreciated!

  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Sure-fire is not in my vocab., but I have reversed some 1/2 h, cap start AC motors. Reversing by reversing start winding. One leg of cap goes to start winding, other ,leg goes to switch,other end of start ties to run winding, generally at one end of core and on surface but laced down. May find another lump in winding-an internal thermal switch near junctions.If you find the ends, cut & attach color-coded leads to each side of cuts. Two of the leads will be the start winding, attach to armature of DPDT sw, other leads to cross-strapped terminals.
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    Power tool motors are usually 'universal' style with commutator and brushes.

    If they are this type, you just need to swap the connections to the brush holders to reverse them.

    There again, I've never seen a power tool with a voltage selection option - in Europe they are sold for either 115V or 230V.

    Senior Member

    May 15, 2009
    Hi, It is realy that simple. Change one set of wires, not both because you then cancell out the effect. For more info look at the AC section at the top of this forum, section 13, tesla motors. It explains it all.
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
    Reversing the disc sander may cause the pad to unscrew from the motor arbor.
  6. jeka616

    Senior Member

    Jan 14, 2009
    Hi all.

    Exact same scenario. I got a "Naniwa" (chinese?) single phase AC motor. I tried to reverse the rotor connections (brushes) as I figured out this is the way it is done in hand drill.

    The problem is, it runs fine in normal, but when I reverse, brushes spark out, and it gets warm (still rotates, with a little less RPM).

    My fear is , this is uni directional motor. Is theere any way to change winding? I guess need to get my head around winding the motor...just don't have time. So previous experience is much appreciated..


    AAC Fanatic!

    Jul 1, 2008
    I don't want to muddy the waters here but the following information is very important if an induction motor is a 120/240VAC motor.

    The Following Applies To Most Cap Start Induction Motors:

    These motors employ three Stators.
    Each Stator is rated at 120VAC.
    When wired for 120VAC all Stators are in parallel with each other.
    When wired for 240VAC both Run Stators are wired in series (properly phased) and the Start Stator is wired in parallel with one of the Run Stators. This forms an inductive voltage divider to provide 120VAC to the Start Stator and its Start Capacitor.

    Clearing Up A Misconception:

    Many laymen and techs alike might think by looking at the windings (wire gauge),...that the Stator-s with the heavy gauge windings would be the Start Stator. This is because laymen and techs alike know that the Start Stator draws much more current than the Run Stators, so they think heavy wire. This would be wrong though. The Start Stator is the one with relatively small gauge wire, as compared to the Run Stators. Because of this the Start Stator is highly resistive which burns up real power and brings E and I closer to being in phase.

    Which Stator (Start or Run) Should Be Switched To Reverse Rotation:

    It is generally accepted that the Start Stator phasing be switched. That said, and I've not tried this, but if the motor is up to speed and you did reverse the Run Stator, nothing would happen. The motor would continue to run in the same direction. This is because the direction of the Rotor is dependent on the phase relationship between the Start and the Run Stators at startup. Since the Rotor is up to speed the Start Stator is switched out of the circuit by the centrifugal switch. It thus becomes meaningless.

    Note: It is not impossible for a dual voltage motor to employ two 120V Run Stators and two 120V Start Stators but I've not seen one. They would necessarily be larger, heavier and more costly.

    I've attached a schematic that I drew some years ago for one of my lathe groups, as this question comes up often.
  8. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    T5 and T8 are typically your start winding, with cap and switch in series. Reversing those leads are the easiest to reverse. Alternatively, you can switch polarity on your fields.
  9. jeka616

    Senior Member

    Jan 14, 2009
    I had a chance to review AC motors section here. The motor I got is, single phase series motor. there are 2 symmetrical stator windings, and one rotor with brushes.

    Attached is a little schematic.
  10. jeka616

    Senior Member

    Jan 14, 2009
    it is rated 220v/0.5 amps. I connect 2+5, 6+4, and connect 1,3 to 220v AC. Runs fine, 18,000rpm as stated.

    TO reverse, I connect 2+6, 5+4, and 1,3 is 220v. It runs about 11,000 rpm, brushesh spark out , and gets warm soon.
  11. CDRIVE

    AAC Fanatic!

    Jul 1, 2008
    Please don't take this as a chastisement, but you should not hijack other members topics. You should have started your own thread, especially since the OP's motor is an induction motor and yours is not. This will also reduce confusion about who's asking what..
  12. jeka616

    Senior Member

    Jan 14, 2009
    usually admins asks searching for thread, before creatig a new one, especially if they are similar..

    ok, new thread will be created. And this is taken as positive feedback