DC motor brush replacement
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  1. #1
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    (Man, it's been quiet around here. Folks in their shops?)

    After resolving (I hope) most of the drive problems in my 1956 all-tube 10EE drive I am now on the other end. The motor works great in reverse but the brushes arc a bit in forward. Starting it doesn't arc at all in reverse but gives one heck of a flash in forward.

    The commutator isn't scored, the separation between bars looks good, but it is dark and not what I've heard described as a light oxidized copper color. The brush edge looks a bit chipped to me, but then I don't know a lot about DC motors.

    I figure that the right thing to do is to replace the brushes. At the same time I'll clean the commutator with an 'eraser' (sometimes called a pumics stone, etc.) to clean metal. I figure on running in the new brushes for a couple of hours if that sounds appropriate.

    Right now I'm waiting on price quotes from Monarch and Reliance, hoping to hear from them today so I can see these things next week.

    Any pointers on replacing the brushes? I'd rather avoid removing the motor from the lathe due to physical constraints, so any info on doing it in place would be helpful.

  2. #2
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    I wish I could help you, but I just took mine down and had it completely rebuilt. Seems it was totally shot and needed everything. It is a big 5 hp GE unit and as far I know, the rebuilders had no problems
    finding any parts. Shermco Ind. did the work
    and it looks like a new motor, inside and out. Not cheap though, but I only want to have to do this once. Daryl

  3. #3
    J Tiers Guest

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    If you can get a clear close-up picture of the commutator, email to me and maybe I can give a thought.

    The pattern on it often tells a story as to what the problem is, or if there is one.

  4. #4
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    Here's a link to a photo of the commutator. It looks worse in this photo
    than it does in person...

    http://www.swcp.com/~russk/commutator.jpg

    A second shot that might elicit some comments:

    http://www.swcp.com/~russk/brushes.jpg

    And for those really daring folks, a bad mpg of a startup showing the brush flash:

    http://www.swcp.com/~russk/start_up.mpg (this is 2.5M, so it's not for the modem user)

    I've ordered the brushes on the simple theory that new brushes never really
    hurt. My plan is to clean the commutator with 'chalk' (that's what I've
    heard it called, but it's not chalk) and install the new brushes, then run
    the motor at a medium speed for a couple of hours to break it in.

    I'm not completely sure how to pull the brushes on this guy, but I figure
    that I'll get to know soon enough.

    Comments?

  5. #5
    J Tiers Guest

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    Well, that picture looks like you have

    Some grooves worn in

    light tracking

    Copper drag

    bar edge burning

    If the real thing doesn't look that bad, take this with a grain or two of salt.

    It looks like a candidate for turning the commutator. The grooves will wear into the brushes and won't be corrected with new brushes.
    Turning it will correct the wear patterns etc, and then you can see if it still arcs with new brushes properly positioned.

    Yopu don't have "ring fire" where the arc follows around the commutator, unless I missed something in the videa. Looks like it is just by the brushes, and mostly by one set.
    Ring fire indicates often either a ver dirty commutator with conductive stuff in the slots, or an open winding.

    Anyhow...
    Copper drag is a rough edge of the bar due to copper being pulled over the edge as it wears. It can lead to arcing.

    The edge burning is from arcing, which may be due to mis-positioned brushes.

    Tracking is lighter and darker parallel streaks.

    Your video file does look to show excessive flashing, something isn't right. If it does it on startup and quits once running, it will probably do it under load also. There is a lot of current when starting, so arc potential is larger then.

    That commutator would probably be scheduled for maintenance if it were on a locomotive. The brush positions or seating may need checking also. Maybe they are worn and cocked in the holder, so that they are mis-positioned.


    The vdeo looks to be taken from the end of the motor. At least, I don't think I see the width of the brush, I see mostly reflections.
    Can you get a better view of the width of the brush?
    I might think differently if I saw that.


    [This message has been edited by J Tiers (edited 07-14-2002).]

  6. #6
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    I'll try to get a new movie done - the problem is that I have to hold the camera while I turn on the lathe and my arms aren't long enough to reach inside the lathe to get a good commutator shot.

    In the meantime I'm still wondering why I get arc in forward and not in reverse. Same inrush current but in reverse it's a smooth startup and in forward there's a lot of arc. Same deal accelerating the lathe, of course.

    I'd like to avoid pulling this motor if there's any way to do so - I'm none too sure I can manuever my hoist in there and I'm not fit enough to lift it out myself, the dang thing must weigh a couple hundred pounds.

  7. #7
    J Tiers Guest

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    Ah, you said a magic word.........Actually I think you repeated it, and it took this long to sink in.

    Only in one direction does it arc.

    The brushes are , for some reason, in a better spot for the non-arcing direction. There is a neutral position where arcing is minimum and commutation is best both ways. Seems yours are possibly not in it.

    Check if the brushes have side wear so that they wobble. This could affect it, sliding sideways somewhat in the arc direction.

    Or if they cock, they might catch and bounce in one direction, causing arcing.

    Or I suppose someone could possibly have managed to move the brushes to a point better for the one direction. The holders looked pretty solid, but I don't know if they are maybe mounted on a ring that moves.

    Also, I saw where you said you DIDN'T have grooving, but the pic looks like you do. Maybe the pic looks a LOT worse than it is. Might be the lighting.

    If so, maybe you are OK if you clean it up and pick the grit out of the slots.

    I still think you have some copper dragging, as I think I see some uneven edges on the bars. And it looks like the edges of some bars at least, have arc damage.

    I would also swear I saw that the brushes had worn in a groove with a "curb" at the edge of the brush. New brushes might not seat right until that edge was worn into them, or the bars turned down even. Must be the lighting.
    You can see the real piece, I only see the pic. You have to judge.

  8. #8
    J Tiers Guest

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    What if anything is new on the brush and arcing problem?
    Just kinda curious what you found, if anything.

    Jerry

  9. #9
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    I've got the brushes on order, expecting them in during the next week or so. At that point I'm going to pull the motor and have the commutator turned, replace the bearings and put in the new brushes.

    I suspect that the problem is a eccentric commutator and some brush issues, maybe too light a tension. I figure that I'll just kill all the birds at the same time so I don't have to pull it out, put it back in just to repeat things.

    This weekend I'm pulling the saddle to work on the oil lines, replacing the Bijur units and cleaning things up to working status.

  10. #10
    J Tiers Guest

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    Did you order from Monarch or another source?

    I ask because I do not currently have a source for odd brushes in orphan equipment, and am looking for one. If you had an independent source, I would be interested in what it is.


  11. #11
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    The Monarch price was a bit out of my range ($40 per, and I need 4) so I took the motor serial number and called Reliance. Their price was a bit better ($18) but I didn't hit their $100 minimum, so we looked for someone local and found Motion Industries. They get a better discount, and pass some of it along since I'm paying about $12.50 per brush from them.

    Monarch sometimes has a better price on things, sometimes a lot worse. The oil metering units in the saddle were cheaper from Monarch than from Bijur; both were cheaper than I expected.


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