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Testing a Universal Brush motor

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  • Testing a Universal Brush motor

    I have a universal Brush motor I would like to test to see if there is anything wrong before I power it up.... Visually nothing looks amiss, the commutator is not burnt and looks OK

    It is out of a Biax 7EL that I got off ebay for a couple of hundred $ in an unknown condition, but it looks like the only problem may be a buggered bearing on the motor, but I would like to test the motor before I switch it on (and also as I cannot get a replacement bearing for a few days)

    So what do I test with the multimeter???
    Last edited by .RC.; 02-12-2010, 01:19 AM.
    Precision takes time.

  • #2
    Hook it up for a moment to a car battery. It should at least make an attempt to turn without the danger of throwing a rod or something.
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    • #3
      Connect it to a lamp dimmer. That will allow you to ramp up the power in a controlled manner.


      • #4
        If the bearing at the commutator end is buggered I would suggest not spinning the motor up as too much movement may end up with a stuft commutator or brush assembly.

        If it turns easily enough by hand just put the multi meter across the terminals on the Ohms range then rotate the motor slowly by hand. I would expect to see points of lost continuity if there are any open coils or stuft commutator segments.


        • #5
          I may have found the problem... A lot of the commutator segments do not conduct.... Upon inspection where the commutator copper bits join onto the wiring the joints are not conducting electricity...

          Should these joints be soldered??

          Precision takes time.


          • #6
            That looks nasty. It may have overheated and thrown off the solder. The commutator needs to be skimmed with preferably a diamond tool and then reslotted. Don't try to clean the commutator with any sort of abrasive. It will embed small particles of grit in the copper that will grind down the brushes quickly. You can try resoldering the wires but use a tin/silver solder. It has a higher melting temperature and is physically stronger than tin/lead. Use an acid flux to make a good contact but then after soldering wash down the commutator area with a boiling hot solution of baking soda.

            You will need at least an 80 watt iron to solder that.
            Last edited by Evan; 02-12-2010, 08:10 AM.
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            • #7
              It looks like the commutator has been turned down a lot already. It may be a good idea to solder them first and check the coils before you do any more work to it. It may have to be rewound and may be cheaper to buy a new armature.
              It's only ink and paper


              • #8

                An earlier reply says the connections have been hot and all the solder has been removed by centrifugal force. A bad bearing could have overloaded the system. Carefully clean the connections and solder the connections. Use a "Growler" to check the armature for internal shorts. If all is OK then wrap the newly soldered joints with a cord and cover with Glyptal varnish.



                • #9
                  Also.. probe (wiggle) each of communtator segments to see if any are loose from overheating or whatever.
                  Last edited by lakeside53; 02-13-2010, 12:13 AM.


                  • #10
                    Originally posted by Evan
                    That looks nasty. It may have overheated and thrown off the solder.
                    I don't think they have ever been soldered.... There is no solder anywhere, and no sign of any overheating..

                    I may have got onto a second hand armature, as no parts including brushes are available new for this model Biax.. Second option is I can get the machine rewired for 240V for about a couple of hundred $..
                    Precision takes time.


                    • #11
                      The thin wires were definitely soldered to the thick staked-in wires...... Looks a little screwy, though, I can't be sure if that is a lousy repair, or a badly failed original assembly.

                      Keep eye on ball.
                      Hashim Khan