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Any way to tell if a motor is reversible in absence of a diagram?

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  • Any way to tell if a motor is reversible in absence of a diagram?

    Is there any way for me to visually tell if an electric motor is reversible by taking it apart and examining it? I have a surplus motor, I was hoping to fing a diagram inside the junction cover but no such luck.

  • #2
    Most motors can be reversed. we need more inforamtion to tell if yours can be. Give us everything on the name plate, dis-assemble and you will find that there are wires to the stator (field wires). Measure the resistance between the wires (here is where even a cheap digital ohm meter shines). measure every wire to every other wire and record the readings. Tell if it uses brushes or not. If the wires are not color coded then use tags or tape to id the wires.

    you might usethe below format to send info:

    lead #
    lead # red blue 1 2 3 4 green
    red 0ohm 9ohm % % % % %
    blue 9ohm 0ohm % % % % %
    1 % % 0 7 % % %
    2 % % 7 0 % % %

    % means off scale or infinity

    About the only time a single phase ac motor can not be reversed is when the factory made internal connection and yo can not get to the wires to re arrange them. This is another "if you must ask then probaly you should get help from some one who can keep you safe". BUt you ask and you do the work and you take the risks not us . Hows that for weaseling out of responsibility?
    BTW: ifit has brushes it a whole different game- probably simpler.


    • #3
      This is a generalization for reversing motor.

      - AC Induction motor (brushless): access to 4 wires required

      - AC/DC universal motor (brush): access to 4 wires required

      - DC brush motor: just reverse polarity

      - DC brushless motor : access to 2 plus a control line.

      Even if only 2 wires are externally available for AC induction or brush motor, and you're feeling brave, you can open the motor and access these winding (bad idea). Hope this helps.



      • #4
        Albert: reason I asked for the info was to avoid the 110/220 situation with the attendant multiplication of combinations. Then there are the "washing machine" two speed set up. But Basically, you hit the nail on its head again!!!!!

        So Abn: if Alberts info ifts use it if not give us more info!


        • #5
          Some caution should be used with DC motors in particular as some are incapable of reverse rotation without damaging the brushes. These motors are often marked with a directional arrow near the shaft or rotation noted on the rating plate.

          The dwell angle of the brushes is never optimum for a bidirectional motor so maximum power will suffer as a result.


          • #6
            THat info chart i posted above did not come out as it looked on my screen. It was supposed to be a matrix with same named leads down and across. the matrix would show the resistance of each winding, connections between the windings, and which were isolated from each other. Sorry, for the sloppy typing.


            • #7
              Thanks, I'll try to arrang it in a matrix when I can make the measurments. My project today was just to find my DVOM...

              The motor is single phase, capacitor start, induction motor.

              It has access to four wires marked T1 through T4.

              T1/T2 and T3/T4 are connected for 115V operation, and T2/T3 are connected for 230V operation. It's manufactured by Doerr.

              Hopefully I can get some shop time tomorrow to take the resistance measurements and arrange the the matrix you describe.

              docsteve66, you hint that the dual voltage operation adds some complexity, can you elaborate if you have time?

              I played with electric motors extensively as a kid, and I have read and am reading electrical texts, I can even give rote answers regarding how electricity works...but for some reason real conceptual understanding of how the different types of motors work has eluded me. Thanks for your help.

              Ps.(I shorted the capacitor with a screwdriver across the leads as a fisrt step to taking apart the motor).


              • #8
                ABN: man you done found and solved the complexity. if you think of the lead t1 as "plus" and the other end of the winding (t3) as minus and do same thing for t2 and t4, you will see tieing t1 to t2 and t3 to t4 is same as hooking plus to plus and minus to minus which means each winding is connected to 110 volts. The other configuration ties plus to minus and then when you conccet across 220 volts each winding "sees" 110 volts. Probably there is a "centrifugal" switch or time delay of some sort to switch the capacitor out of the circuit when the motor reaches near run speed. We need to know where those capacitor leads connet!!.

                At first glance you may have a motors not intended for reversing (the capacitor and start switch) are permenatly wired across one winding. Just cause "they" didn't intend it it to be reversible dont mean it can't be done! tell more!!!!!


                • #9
                  Near me are a lot of people that have water pumps for well water because they do not have city water lines. So there are a lot of one to two horse motors on pumps. The pump seals seem to go bad eventually, but the motor is OK. Lots of two horse 3400 Rpm from pumps around cheap. Unfortunately they are not wired for reversing. I took a working cheap two HP motor apart, traced the start winding ends and reversed them. After tieing down and varnishing the wires it started and ran fine in the reverse direction. Must are flamge mounter so requires an angle mount.


                  • #10
                    bpsbtoolman has the rest of the answer!. If there are only four wires comming out and the motor is 220/110 , you have a slight problem. actualy there are problably at least five wires to play with. THe fifth wire being the one to the start contacts.

                    The trick to all electric circuits is that every wire has two ends- not one or three, despite all apearances to the contary .
                    The other end of the wire commming off the switch and disappearing into the motor windings connects to the end of a motor lead winding some where. find it, disconnect it, and al la bpsbtoolman you can reverse it!!!!