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Commutator readings .

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  • Commutator readings .

    I do not understand why I am getting inconsistent reading (Ohms)from a known good working armature.Is this normal? I have gotten readings as follow:from a low of 0.6 to a high of 14.4. I have used sandpaper to clean the commutator and used toothbrush to clean away any cuttings.
    Thanks for any advice!!

  • #2
    Re: Commutator readings .

    How are you going about taking the readings? Are you measuring across the carbon brushes or from one copper bar to the next one? Are you measuring from say bar 1 to 2 and then 2 to 3 and then 3 to 4 as if they were numbered or are you connecting one lead to bar 1 and then going around the bars such as 1 to 2, then 1 to 3 and then 1 to 4?

    Try setting your meter (hopefully a VOM type such as a Simpson 260 or Triplett 630) to the highest range and connect one test lead to the motor shaft and then touch the other to each bar. Please post results for this test if you can.

    While this may seem extreme take a good look at the commutator under bright light and with magnification. It's easy for a very tiny spec of copper to short two bars together.
    Last edited by Woussko; 05-10-2009, 11:15 PM.


    • #3
      Re: Commutator readings .

      I am checking for shorts or openings so setting a vom at the highest setting would not be appropriate, it would give an infinite reading.The vom should be set at the lowest settings in Ohms.
      The commutator is checked as follow;bar 1&2, 2&3,3&4 and so on.
      I have looked and checked the bars for dust and find nothing.

      N:B I did not use a growler and the armature was checked out of it's housing.


      • #4
        Re: Commutator readings .

        You need to know if the armature is lap wound or wave wound and what the commutator offset is. Woussko is asking you to check if there is a breakdown in the wire insulation and causing a current leak. His test will identify this.


        • #5
          Re: Commutator readings .

          There wasn't any reading(continuity)for Woussko's motor shaft test.
          How could one tell whether the armature is lap or wave wound without a manual and please explain commutator offset.


          • #6
            Re: Commutator readings .

            You can usually determine lap and wave by the motor application.
            High current low voltage will be lap wound.
            Low current high voltage will be wave wound.
            Offset is for lap winding and defines where the ends of the windings meet the commutator. For an offset of one you would measure between plate 1 and 2. For an offset of 2 the winding would be measured between plate 1 and 3 etc.