DC Motor with only one brush?

Discussion in 'General Electronics Chat' started by Gdrumm, Jan 2, 2015.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    It's a Craftsman 20 Volt Drill, Model 900.16496.

    I actually have 2 of them, and they don't work.

    I took one motor apart, and I only see one brush.

    The commutator ring was real dirty also.

    Has anyone seen a motor like this?

    With a bright light, I looked inside motor # 2, and it appears to be the same design.

    Hope my pictures are clear enough.

    Thanks,
    Gary
     
    Last edited: Jan 2, 2015
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    sometimes, they use the bearings o the armature shaft for the other side of the winding.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,503
    2,366
    Are you sure it is not a replulsion induction motor? On these the brushes are not always at 180° but can be 90° or there abouts.
    Is this a 20v AC or DC cordless?
    Max.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    A second brush at 90 degrees would make sense, that would match the geometry of what I'm seeing.
    However, if that's the case, then the 2nd brush is missing, and, it was mounted to the end of it's lead differently.
    Looking at photo 146, I can almost imagine what the brush may have looked like.

    And, if it's a design flaw, that would explain why both of them look the same way.

    Thanks for the feedback.
    Gary
     
  5. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Max,
    It says 20v max DC.

    Where might I find a site that shows small DC motor designs?

    Just curious
    Thanks,
    Gary
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    I'd bet if you look farther inside you'll find more brushes. With only 3 commutator segments, that's probably the "tach" output to the variable speed trigger chip.

    After looking at the manual for this model, you sure it doesn't have a BLDC (brushless dc) motor?
    Some of the new ones with that type short body, do have BLDC motors.
     
    Last edited: Jan 2, 2015
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,032
    1,622
    Your upper brush is missing. I have a number of the craftsman cordless tools and I have had a few apart to clean out, after dropping them in places they shouldn't have ever went, and they all had similar motors but with two brushes.
     
  8. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    Ok if you look at your pics again you will see the 2 copper colored tabs .. They hold the brushes in place 180 degrees from each other and keep pressure on the brushes.. But it looks like one brush came out as the bottom should look like the top half..
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    Last edited: Jan 3, 2015
    Metalmann likes this.
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,769
    1,103
    A conventional 3-pole DC motor like this one.
     
  11. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    The motor seen in Shortbus link is it.

    I expected to see 2 brushes, but saw only one.
    There is a prong on the opposite side f the one brush that looks like it might have held a brush at one time, but now it's just a bare copper prong that almost touches the commutator.

    Both drills look identical, and I took the "sealed" end off one of them to take the photos.

    They both look as though they have had heavy use, so I'm guessing they would require a new "sealed" motor, and they aren't worth spending money on.

    I'll just keep them for spare parts, the trigger, and chuck, etc.

    Thanks for all he input.
    Gary
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    In a high torque item like a drill/driver?
     
  13. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,032
    1,622
    Well obviously yes. :p
     
  14. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    Can you make a set of brushes for it. If there is a starter/generator rebuilder in your area, they are purchasing from large brush manufacturers and buying brushes very cheap. Perhaps you can find something close and fabricate a decent fit. Just make sure the composition is correct.
     
  15. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    How is he suppose to do that ???
     
  16. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,032
    1,622
    Given the vast quantities of these drills that can be found for next to nothing on eBay I would just pick up a few more parts units and build a few good ones from them and call it good.

    If you have two now two more should score you enough parts to make at lest one good drill, if not two, plus give you some good pieces to play with afterwards.
     
    Metalmann likes this.
  17. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    If you look at the brush and have it in your hands, you can get an idea of how much carbon is used in the brush. You have to take into consideration the voltage and amperage being used but one can get a pretty good idea of the composition of materials used. Sometimes we have to experiment to get something that works when we can't find it in the marketplace anymore.
     
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,769
    1,103
    If two motors have failed in the same way then there's not much point duplicating the existing brush arrangement: something of better quality is called for if you want greater durability.
     
  19. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    The brushes are inside a small sealed motor.
    I did take one apart enough to be able to clearly see that the carbon part on the brush was missing.
    It was weird, it looked like the carbon was molded into a thru hole in the brass or copper arm of the brush assembly.

    I didn't dig any further but perhaps I can make one motor work if I can remove the brush and arm, and mount it in the other drill.
    I'll take a closer look later this week (when the weather permits).

    I do have a few brushes (carbon) that I've salvaged, and some softer ones that I bought.
    But I don't think I could make one fit this weird application.
    Can they be glued to an arm? With Super Glue?

    Thanks
     
  20. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Not likely because superglue is not a conductor of electricity and the lateral forces are significant.
     
Loading...