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 -

 

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.

 

That does seem excessive. How do the brushes look?

 

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.

 

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.

 

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.

 

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.

 

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 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.

 

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.

 

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

 

The brush compositon is:
Copper 50%
Graphite: 40%
other: 10%

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

 

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.

 

Look at brushes with motor running in the dark.

 

That is usually the carbon etc atomizing and essentially burning up.
Max.

 

The brush compositon is:
Copper 50%
Graphite: 40%
other: 10%

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

Graphite is the last thing that could melt it has melting point of 4000C and its used on rocket nozzles.

 

The graphite in my pencils??!!! Wow!

 

The graphite in my pencils??!!! Wow!

Not the same thing. Graphite is available in many different forms. Pencil 'lead' is based on a natural graphite/clay mixture. The Graphite in a rocket nozzle is a synthetic graphite, a by product of oil refining.

 

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.

 

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".