Brush problems in motor

Discussion in 'General Electronics Chat' started by matt chrome, Feb 22, 2010.

  1. matt chrome

    Thread Starter New Member

    Feb 6, 2010
    4
    0
    I wonder if someone can help me? I am repairing a mobility scooter that is fitted with a leroy-somer motor, (circa 1998) it`s an MBT1141M which works perfectly (seems to run cool too) after the brushes have been freed in their holders, but each time I free them, and work them up and down until they are loose, and refit them, the motor works perfectly for my test drive, but as soon as I test the motor again the next day, some of the brushes have stayed up in their holders again! I did try increasing the spring tension on the brushes by putting the springs on the next notch, and I thought it had cured it, but no. Incidentally the Brushes are near new. Do you think that they might not be correct for this motor? The brush holders seem a little burnt at the point where the brush enters, this is the point where they get stuck.
    Hope someone can help.... Matt
     
  2. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Smooth the end of the brush holder that is burnt?
     
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  3. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    you could probably use a small file (fine toothed one, like a jewelers file) to clean up the brush holder hole... I had to do that to one of my makita 4" and one of my dremmels...... basically those "brushes" should move up and down the without too much restriction, brushed motors all seem to work the same way so this should solve your issue.....
     
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  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If there is any roughness in the brush holder due to corrosion, arcing, or whatever - it will wear a notch in the brush material which is soft - and the brushes will hang up, or simply wear out far faster than they should.

    As BMorse suggested, a fine-toothed file could be used to remove the worst of the corrosion - however, you should also polish it until it is very smooth, so the brushes won't wear prematurely, or get "hung up" on any rough spots. I suggest using progressively finer wet/dry sandpaper.

    You can trim the wet/dry sandpaper to size using a disposable snap-blade knife from the backside, and glue it to a scrap of wood like a popsicle stick.

    Avoid using emery cloth, flint or garnet sandpaper, as these type papers will embed grit in the material that you are trying to smooth down.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    It should be obvious, but do avoid oiling the brush to help it slip freely. That just insulates the brush and makes a clean up problem.
     
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  6. matt chrome

    Thread Starter New Member

    Feb 6, 2010
    4
    0
    Hi SgtWookie,
    Thanks for your response, I have since been in touch with Leroy-Somer the motor manufacturers to ask why this problem is occurring, and was told that sometimes the commutator becomes glazed with use, and recommended I have the commutator skimmed. I am thinking why not clean the commutator myself, as there is ample room through the Large brush holder holes, and I can easily turn the armature round with the cog on the end, But now I would like to know what to clean it with, and what sort of finish should remain?
     
  7. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    the commutator is what the brushes come in contact with, this should have nothing to do with the brushes getting stuck in their "holes", they should be able to move freely up and down without any restrictions. If they don't move freely, then they will not make proper contact with the comutator and the motor will not turn...

    If it was a commutator glazing problem, then the motor will not run properly even if the brushes moved freely. You may encounter a "stuttering" problem with the motor (where the brushes will meet up with a glazed section of the commutator preventing it from making contact.) if this was the case......

    My .02
     
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  8. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Two things to check:

    Motor commutators are usually 'undercut' - the insulation between the metal commutator segments is cut down below the level of the metal so the brushes only ever touch the metal contacts.

    If the grooves are clogged up, they should be scraped out, as the packed carbon dust shorts things out.

    The other is to check the 'pigtails' on the brushes are properly connected.
    All but very low power motors have braided leads built in to the brushes, these shoudl fit to screws on the brush holder frames.

    These give a direct connection so there is no current flow through the sliding surfaces on the sides of the brushes.


    As Sarge says, make sure there is no oil anywhere near the brush holders. If brushes come in contact with any amount of oil, they are usuall wrecked. It soaks through them and they start to wear extremely fast, depositing carbon paste everywhere.
     
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  9. matt chrome

    Thread Starter New Member

    Feb 6, 2010
    4
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    Thanks for your reply, Actually, I should have said, the last time I tried the motor, it was reluctant to start, but upon checking the brushes, they were actually free. Leroy-somer were giving possible reasons for this as well as the brushes possibly getting hot, thus burning the brush holders causing them to stick. But I still would like to know if a polished finish, as with chrome cleaner would be OK, or should I roughen it up a bit with something? Thanks........ Matt
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Motor shops use various grades of commutator cleaning "stones". Some are pumice stones to help contour the brush to the commutator after brush replacement and others are various hardness rubber rods with abrasive materials embedded. These remove the surface contamination from the commutator without removing any of the base metal. Check with your local motor shops and see if they will sell what you need. Go here http://www.mcmaster.com/#chalk-stones/=5zgsyt and look about half way down the page for Commutator Chalk Stones or a little further down the page for Commutator Cleaning Kit.
     
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