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wiring motor for reverse

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  • wiring motor for reverse

    Hey there,
    I left my 4x6 bandsaw unsupervised for a moment and returned to a smoking motor! Saw had jammed in the cut, motor is burned out.
    Found an old motor, installed it, but it turns the wrong way. This is an older motor, with 4 wires coming from the windings
    Click for full size - Uploaded with plasq's Skitch
    Click for full size - Uploaded with plasq's Skitch
    There 2 wires going to terminal 1, one wire going to terminals 2 and 4. What isn't shown is the power input, ungrounded going to terminals 3 and 4.

    What if anything must I do to reverse rotation of the motor?

    Thanks, Paul

  • #2
    That appears to be a shaded pole motor (type SP on tag), and they can't be reversed.

    Any products mentioned in my posts have been endorsed by their manufacturer.


    • #3
      SP also might be "split phase", which will agree with the power (1/4 HP) and the number of wires (4). I have never seen a 1/4 HP shaded pole motor.......... 1/20 hp, yes. 1/4 HP, no.

      The way a split phase is reversed is to reverse the wires that go to the start winding, but NOT the wires to the run winding. it is the relative phase between them that determines rotation, since the motor will keep going whichever way it is started.

      Two wires need to be reversed in connection. The best way, with an unknown motor, is to use an ohm-meter and determine which 2 are part of one winding. You likely want the winding that goes from 1 to 2.

      One of the two wires on terminal 1 should have continuity to terminal 2, and those two are probably the ones to be reversed.

      When it is right, the motor will start and you will hear a click as the start winding is switched out, at which time the current draw will drop down to the "run" current. (Start current is always high).

      Keep eye on ball.
      Hashim Khan


      • #4
        That being a Canadian motor, it may only run in reverse trying to get back to Canada...

        Yes.. proper way to reverse motor is swapping start-capacitor-winding ends connections.. making the capacitor on the "other side" of the start winding from the power... it (capacitor) sort of delays the power pulse from the run winding making it take off in "that" direction..

        No capacitor (bump) on outside of motor, none in pecker head.. no reverse..

        The thing-a-ma-bob there with the red button is the overload.. press it if it won't run.
        Excuse me, I farted.


        • #5
          The longer wire going to terminal one is most likely one side of the start winding if so it would go to terminal two to reverse the motor. First us a ohmeter to prove. With the long wire removed from terminal one you should have a reading between 1 and 2 LOW OHM"S and HIGH OHM"S or no reading from 1 or 2 to the other wires. Reason I say high ohm's is the start winding is probably connected to the center of the run winding.



          • #6
            Motor reverse


            As J. Tiers said, you need to reverse the starting winding. Usually the starting winding has smaller wires than the run winding. You may need to open the motor to find this winding. It is conceivable that one end of the start winding may be tied to one of the run winding terminals, in which case you will need to disconnect it and change it to the other run terminal.

            Jack C.


            • #7
              I've run into a few of those split phase motors, especially those for applicances and pumps, that have a common lead for start and run windings, buried deep enough that for all practical purposes they are non reversible. If you don't see a pair of wires for reversing, there's a good chance you're out of luck.


              • #8

                First of all, thanks to all who replied, this is an amazing resource.
                With all wires removed from their terminals, no audible continuity from any of the windings? Not looking good. So, took the long wire from term 1, move over to term 2. Plugged motor in briefly and got loud humm, no rotation.
                I'm going to start looking for another motor.
                Again thanks for the help.


                Ps. Does anyone own and reccomend this book:
                Or any other suggestions?


                • #9

                  Open the motor and determine which pair of wires go to the Start section. You probably need a better meter as you said there was no reading with the meter but when power was applied there was a loud hum.

                  I would go for another motor as the name plate shows the unit to be only a 1/4 hp motor. Not enough power for a band saw.


                  • #10
                    Originally posted by J. R. Williams
                    You probably need a better meter
                    A split phase motor has a higher-resistance and a lower-resistance winding. The high resistance winding is the start winding. The motor generates a phase shift (and therefore a rotating magnetic field when starting) because the time constants (L/R) of the two windings are different. So the resistance of the wire in the start winding does the same job as the capacitor in a capacitor-start motor.


                    • #11
                      Flipping the blade inside out should reverse the teeth. Dunno 'bout the blade guides, worm gears and the blade drive wheels...they might not like it.

                      "Accuracy is the sum total of your compensating mistakes."

                      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton


                      • #12
                        Old farmers trick,longer belt twist it in a figure 8.
                        I just need one more tool,just one!


                        • #13
                          Not sure you should give up, assuming that it works as-is. If it does, as you say, then you KNOW that is is a good motor, and any oddities with wires are separate.

                          One connection may be permanent, from line through the thermal (red button) and to one end of run winding. Either terminal 3 or 4 should be that.

                          There are enough wires to do the job, since it is a one-voltage motor (see dataplate).

                          So make sure your ohmmeter is good, and check again.

                          You should probably find a wire that connects to either 3 or 4 per ohmmeter, and two wires that show a low resistance of possibly 7 to maybe 20 ohms between them.

                          My guess is that one of the wires on 1 and the one on 2 need to be reversed, but this should be confirmed by ohmmeter.

                          Normally, if the motor cannot be reversed, they don't bother with the wires and terminals. Since that HAS these extras, it probably reverses.

                          1/4 HP is too small for a mill too....... But someone forgot to tell my mill, which happily takes large bites of unwanted metal when I ask it to, and has never stalled. I suspect that the gear/belt ratio on the saw will fix a lot of power issues......... It does on the mill.
                          Last edited by J Tiers; 05-12-2008, 08:04 PM.

                          Keep eye on ball.
                          Hashim Khan


                          • #14
                            OK, I'll have another go tomorrow.


                            • #15
                              These are the known facts.

                              1. The motor works, just runs backwards.

                              2. One side of the running winding goes through the RED overload button.

                              3. One side of the start winding goes through the centrifugal start switch.

                              Buy or borrow a volt ohm meter. Radio shack Home Depot start at about $10.

                              Label all the wires. Write down where they are now connected. Disconnect the wires from the terminals.
                              Using the ohm meter hook one lead to the wire that went to the over load switch. Find the wire that is the other side of the run winding. There should be only one that you get a reading on. These wires correspond to 1& 4 on a wiring diagram. Now hook the lead of the ohm meter to the wire that comes from the centrifugal switch and find the other side of the start winding. These wires correspond to 5 & 8 on a wiring diagram. To make the motor run 1 and 5 are connected together and hooked to line 1. Then 4 and 8 are connected together and hooked to line 2. To reverse direction 1 & 8 go to line 1 and 4 & 5 go to line 2.

                              This is for the motor in your picture. Looks to have only four wires from the windings. If it has three wires from the windings the procedure changes, but it is still reversible.