Gunk found in a small dc motor

Thread Starter

JohnBedell

Joined Oct 15, 2012
7
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 -
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
22,669
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.
 

Thread Starter

JohnBedell

Joined Oct 15, 2012
7
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.
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
22,669
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.
 

bwilliams60

Joined Nov 18, 2012
1,389
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.
 

THE_RB

Joined Feb 11, 2008
5,438
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.
 

wayneh

Joined Sep 9, 2010
17,052
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.
 

THE_RB

Joined Feb 11, 2008
5,438
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. ;)
 

MaxHeadRoom

Joined Jul 18, 2013
22,669
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.
 

tom_s

Joined Jun 27, 2014
288
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. ;)
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
 

Thread Starter

JohnBedell

Joined Oct 15, 2012
7
The brush compositon is:
Copper 50%
Graphite: 40%
other: 10%

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

MaxHeadRoom

Joined Jul 18, 2013
22,669
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.
 

takao21203

Joined Apr 28, 2012
3,700
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.
 

Attachments

Thread Starter

JohnBedell

Joined Oct 15, 2012
7
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.
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".
 
Top