electric drill repair

Would someone please tell me possible reasons for excessive brush sparking? The commutator has been cleaned bright and shiny with a white stick product made for this purpose. The insulating segments of the commutator do not appear to be higher than the copper segments. All dust and grit have been removed with an air gun. The brushes are new and appear to be properly seated. The AC supply is steady at 121 volts. And yet there are still half-inch yellow-orange sparks coming from the commutator/brush contact area. I thought I knew a few practical things about small electric motors but I'm out of my league with this one. Any suggestions will be appreciated. Data Duck
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DataDuck wrote:

it seems to work for me.. get all the dust from the carbon brushes off as the dust will let electricity flow and this might be where the sparks are coming from????
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DataDuck wrote:

These are just WAGs, but here's a few more possibilities:
1. The comutator may be out of round or the bearing at the commutator end of the armature is sloppy, making the commutator fling the brushes off.
2. Could the brush springs have lost their tension and not pushing the brushes against the commutator firmly enough? I presume you checked the fit of those new brushes in the brush holders and they aren't "sticking" in them.
3. (And this would be bad news.) Perhaps the armature has an internal short in one or more of the windings. You can try measuring the dc resistance from bar to bar around the commutator and see if they are all equal.
Good Luck,
Jeff
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Jeff Wisnia (W1BSV + Brass Rat '57 EE)

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I'm surprised no one mentioned that, with new brushes, it's normal to a degree, until they get worn in and accurately conform to the shape of the comm? I've never seen new brushes that didn't spark for the first few hours of use, esp if it's heavy use. Pop
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On Mon, 19 Jul 2004 23:32:10 -0400, "PopRivet"
snip

<cough>..umm PoP.. the OP did say "properly seated" :->I am going with #3,, a shorted coil. This baby is for the tip/dump/garbage..so sad :- )
For the OP..get your piece to a tech shop and ask them to run the armature over a growler,, ...pounds to peanuts its pharked :->
cheeerio Pop :-)
BTZ
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bitzah wrote:

1) to remove the brushes and look at the contact surfaces, or 2) to use the device until the sparking subsides. --Phil
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Phil Munro Dept of Electrical & Computer Engin
mailto: snipped-for-privacy@cc.ysu.edu Youngstown State University
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Phil Munro wrote:

You can use a "brush seating stone". Maybe that was the "white stick product" the OP mentioned using. You touch it to the commutator with the motor running. IIRC there's an abrasive in it which laps the ends of the brushes to match the commutator. Perhaps he used one, but only cleaned the commutator with it before he installed the brushes.
I used to have one of those stones, but it "grew legs" and walked away maybe 30 years ago. I was suprised that I could only Google up one place selling them, and that's in England. It's the first item on this page:
http://www.rthursby.co.uk/acatalog/R_Thursby__hand_held_testers_and_sundries_46.html
Maybe they call them something else nowadays, but there were plenty of Google hits for "brush seating stones" describing their use on things like vacuum cleaner and power sander motors.
We are probably beating this one to death by now, huh?
Jeff
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Jeff Wisnia (W1BSV + Brass Rat '57 EE)

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On Tue, 20 Jul 2004 13:41:42 -0400, Jeff Wisnia

yeh,, cluelessly ! :->
BTZ
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On Mon, 19 Jul 2004 20:14:59 -0700, Jeff Wisnia wrote

To provide a bit more detail...
Measure resistance with a multimeter across each pair of commutator contacts (the two contacts opposite each other that the brushes would contact in normal operation), all around the commutator. Also measure resistance from each commutator contact to the steel of the armature (the fattest diameter that all the copper wires are wound around), or anywhere on the shaft.
If you get any continuity (low resistance) on any of these measurements, it's either rebuild time (probably not worth it unless it's a dedicated tool that's not made any more), or replacement time.
In future, with a topic like this you might want to try a NG such as sci.electronics.repair. They cover this topic quite well, and you'd get lots of great advice from those folks (not to diminish the great suggestions you've gotten here...)
Good luck,
--
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DaveC wrote:

Uh, I'm always willling to learn something new.... Your correct is saying there should be no continuity betwen any commutator bar and the steel armature core.........
But, if that motor's got its brushes opposite each other (180 degrees apart) like most drill motors do, then you'd darn well better see some continuity between any two commutator bars "opposite each other". If there wasn't, the damn thing couldn't start, could it?
Jeff
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On Tue, 20 Jul 2004 08:47:03 -0700, Jeff Wisnia wrote

Dang, I hate it when I do that...
You're right, of course. I should have said:
Measure resistance with a multimeter from each commutator contact to each of the other contacts, all around the commutator. If there's continuity between any two commutator segments *except* the ones directly opposite, the armature is bad.
If there is no continuity between each pair of contacts opposite (180 degrees across the commutator), the armature needs repair.
Also measure resistance from each commutator contact to the steel of the armature (the fattest diameter that all the copper wires are wound around), or anywhere on the shaft. There should be no continuity at any point measured here.
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DaveC wrote:

Gee Dave, I hate to keep doing this to you, but the folks reading our posts should be given information that is accurate.
The diagrams about halfway down this page clearly show that there are many different armature winding schemes, but all of them will result in continuity between bars *other* than the ones directly opposite each other.
http://www.reliance.com/mtr/mtrthrmn.htm
No offense intended,
Jeff

Yep
Another yep..
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On Wed, 21 Jul 2004 15:47:51 -0700, Jeff Wisnia wrote

None taken.
It seems the best way to determine a shorted (or open) field is to measure the resistance between each (opposite) pair of commutator contacts. All measurements should be the same. A different (higher or lower) resistance measurement will indicate a shorted or open armature winding.
There's a handful of good information on troubleshooting universal motors -- which this one, I think -- here:
http://www.repairfaq.org/REPAIR/F_appfaqg.html#APPFAQG_017
Good luck, DataDuck.
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What makes it excessive, it sounds ok to me.
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Larry Wasserman Baltimore, Maryland
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A bad set of brushes
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I changed the condenser and everything was back to normal.
RBJ

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wrote:

Glad it worked out for u :-)
btz
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