Gunk found in a small dc motor

Discussion in 'General Electronics Chat' started by JohnBedell, Aug 4, 2014.

  1. JohnBedell

    Thread Starter New Member

    Oct 15, 2012
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    Hi,

    To any small dc motor gurus out there...

    ever see a commutator this bad?

    This motor has had less than 2 weeks of limited use.

    I'm not sure if the brushes are made of carbon or playdoh!

    Any insight would be helpful.

    Many thanks -
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    How come the striations on the non brushed section?
    Either the com was cut that way or high copper content brushes were used, OR it is a very cheap quality motor (or all the above)!
    Is there an operating symptom?
    Max.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    That does seem excessive. How do the brushes look?
     
  4. JohnBedell

    Thread Starter New Member

    Oct 15, 2012
    7
    0
    Cheap motor - Yes.

    Symptom - controller senses excessive current and triggers fault.

    I have found that sludge in comm gaps is causing a prolonged "short" during start-up.

    Instead of carbon dust found normally in all motors of this type, I am now finding THIS type of junk. It's almost as if the brushes are too soft or moisture is mixing with the carbon dust.

    Brushes themselves look to be square with no wear - see pics.

    Thanks for the replies.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    From the pictures they do look like very cheap brushes and in fact do appear to have very high copper content, this is usually associated with very high current motors etc.
    You may want to look for a higher quality motor!
    The unbrushed portion of the com also does not look right?
    Max.
     
  6. bwilliams60

    Active Member

    Nov 18, 2012
    851
    136
    The commutator has been cut with a very course finish. On a small motor such as this, it should be a lot smoother one would think. The brushes look to have some odd filler in it which is melting and forming this gunk when current is passed through them. I have to agree that this is a very cheap motor.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Could be some grease got into the brushes or commutator.

    I agree the comm should be finished much smoother. A touch of wet n dry paper in the lathe should do it. And a lot of cleaning before running it again.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    I've never seen brushes that looked like some sort of composite like that. Those are really ugly. I think I'd look for a new motor, new brushes, or both.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The brushes look ugly in the closeup but they are just standard sintered brushes.

    Once the comm has been smoothed up and the brushes run in for a while it should be fine. People forget brushed motors need to be run in. Or just don't care any more. ;)
     
    Metalmann likes this.
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I still do not think that is a normal appearance for a com, especially one run for a couple of weeks use.
    And with the appearance of the brushes, it smacks of El-Cheapo to me.
    Max.
     
  11. tom_s

    Member

    Jun 27, 2014
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    381
    the gunk looks it had chunks of commuter in it. maybe the brushes are not running true and acting like a lathe.

    methinks max has summed it up nicely
     
  12. JohnBedell

    Thread Starter New Member

    Oct 15, 2012
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    The brush compositon is:
    Copper 50%
    Graphite: 40%
    other: 10%

    It looks like the graphite component is melting - anyone agree?
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have never seen chunks of copper in high content copper brushes, the copper usually blends in with the graphite and just takes on a coppery hue.
    It smacks of Very cheap production to me.
    Max.
     
  14. BR-549

    Distinguished Member

    Sep 22, 2013
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    Look at brushes with motor running in the dark.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is usually the carbon etc atomizing and essentially burning up.
    Max.
     
  16. ISB123

    Well-Known Member

    May 21, 2014
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    Graphite is the last thing that could melt it has melting point of 4000C and its used on rocket nozzles.
     
  17. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    The graphite in my pencils??!!! Wow!
     
  18. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Not the same thing. Graphite is available in many different forms. Pencil 'lead' is based on a natural graphite/clay mixture. The Graphite in a rocket nozzle is a synthetic graphite, a by product of oil refining.
     
    atferrari likes this.
  19. takao21203

    AAC Fanatic!

    Apr 28, 2012
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    maybe the brush tension was adjusted wrongly during assembly. Good motors have springs, while cheap motors only have flexible lugs. The brushes look unusual to me. Where does the motor come from?

    Maybe RPM or voltage is too high. Normally the brushes wear out, not the commutator.
     
  20. JohnBedell

    Thread Starter New Member

    Oct 15, 2012
    7
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    The motor comes from China ("Surprise").
    I have seen some of these motors with little or no brush wear coming back looking like this.
    I wonder if the splotchy appearance of the brushes has anything to do with it.
    The copper and graphite appear not to be evenly "mixed".
     
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