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Dc motor brush sparking

DPittman

DPittman

Ultra Member
I've got this little 450watt 90 volt dc motor that I've salvaged and it seemed to have tremendous brush spark when I tried it. The original brushes were worn but there were still some left. The commutator was dirty but very little wear on it, I cleaned it up and undercut the mica a little bit. I've replaced the brushes and it is slightly better but still is not right. I haven't even ran it up to full voltage yet cauz I think there would be a lightning show with smoke.

Do new brushes need a wear in period??
What else could be causing this?

The whistling noise in the background is not the motor but the horrible wind we have right now whistling through my garage door.
 
Take your voltmeter and see if there is conductivity between the motor fame and power leads. Maybe your getting arcing to the frame?
 
Couple things -

you can “lap in” New brushes by wrapping the commutator with some sand paper and working the brush face in.

Check the brushes to be sure they are not worn to the copper

Make sure the commutator is smooth- sounds like some ticking going on where the brushes maybe hitting an edge?
 
is it better or worse in the other direction? some treadmill motors have offset/angled brush holders and will do that if reversed.
 
I haven't tried th
Darren said:
is it better or worse in the other direction? some treadmill motors have offset/angled brush holders and will do that if reversed.
Click to expand...
I haven't tried reversing the motor with the new brushes but I am running it in the direction it was designed for.
 
Brent H said:
Couple things -

you can “lap in” New brushes by wrapping the commutator with some sand paper and working the brush face in.

Check the brushes to be sure they are not worn to the copper

Make sure the commutator is smooth- sounds like some ticking going on where the brushes maybe hitting an edge?
Click to expand...
Yes the commutator is smooth and yes there is definitely ticking associated with the sparking. If there was bad winding/wiring in the motor would it run at all? I haven't done any testing of the armature cuz it seemed to at least run right off the start.
 
I have a hand drill, battery operated, that sparks 10x worse for few years now. Unless you are planning to run it a LOT don't worry about it, just my 2c.
 
Maybe there is something bridged between segments of the commutator? I have seen that cause arcing, before. I would have a closer look maybe run a toothpick or scribe between the segments. There is a commutator grindstone that sometimes settles them down but if there is another problem the stone won't help.
 
Well I'm stumped. I did some tests on the armature with a multimeter and things seem ok as I understand the tests.
Ran a scribe through the commutator segments just to make sure and it appears fine to me.

I even put the armature in the motor housing in reverse order in case I screwed the up. Didn't look right to me but I thought it could have been a possibility. It ran the same but backwards of course. Pictures of the armature in both ways. (1st pic is what I believe is the correct way)
20220406_114912.jpg
20220406_114945.jpg
20220406_113135.jpg


Dang I was hoping this motor was going to work for a tool post grinder project as I figured it was about right size.
 
Sounds like you could possibly use one of these Martindale Undercutters.

Martindale Undercutter.webp


I have one with a couple dozen cutters gathering dust on a shelf - for sale cheap.
 
One cause of excess sparking is the magnetic mis-alignment of the rotor and armature. The air gap should be equal around the rotor and at each end. Assuming perfect construction of the rotor and armature the magnetic alignment would then be correct. On larger equipment the bearings can be adjustable to align the rotor. On small motors the bearings aren’t adjustable and construction is less than perfect so you have to live with what you get.
 
eotrfish said:
Sounds like you could possibly use one of these Martindale Undercutters.

View attachment 22859

I have one with a couple dozen cutters gathering dust on a shelf - for sale cheap.
Click to expand...
Well I've got a homemade facsimile of that..sort of, I have the motor from an old Atlas mica unercutter and I adapted that to my little Asian lathe. I don't have much for the little cutters tho, if you're interested in selling any of yours?
 
Johnwa said:
One cause of excess sparking is the magnetic mis-alignment of the rotor and armature. The air gap should be equal around the rotor and at each end. Assuming perfect construction of the rotor and armature the magnetic alignment would then be correct. On larger equipment the bearings can be adjustable to align the rotor. On small motors the bearings aren’t adjustable and construction is less than perfect so you have to live with what you get.
Click to expand...
Interesting. There definitely is not any adjustment to this motor. Nor can i really see what sort of clearnce there is because the end caps restrict the view to much to really asses.
I'm sure the level of sparking I'm seeing is not acceptable. (But don't let me convince anyone that I know anything about electrical stuff)
 
DPittman said:
Well I've got a homemade facsimile of that..sort of, I have the motor from an old Atlas mica unercutter and I adapted that to my little Asian lathe. I don't have much for the little cutters tho, if you're interested in selling any of yours?
Click to expand...
What size cutter are you looking for?

I have the following...

ARMATURE CUTTERS.jpg

.035 x 1/4 - 4
.023 x 3/8 - 2
.023 x 1/4 - 3
.02 x 1/4 - 1
.03 x 5/16 - 16
.03 x 3/8 - 3
.015 x 5/16 - 34
.015 x 3/8 - 3
.015 x 1/4 -2

All have 0.125" dia. hole.
 
From your picture in message #10 it doesn’t look like the mica needs undercutting. The commutator does look rough which could cause the sparking or maybe it was caused by it. A skim cut to clean it up would be the first thing to try. Final clean up with fine sandpaper not emery paper.
 
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