Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Excessive Carbon Brush Wear

Excessive Carbon Brush Wear

Excessive Carbon Brush Wear

Hello together,

I kindly request your support about following issue.
I am currently working on a project on a DC-Motor (permanent magnets) application.
The problem is excessive carbon brush wear. Both armature and brushes are made of carbon materials and there exists no chemical differences with problematic (excessive worn) and non-problematic dc-motors.

Today I have found out something new but I can not interprete it, therefore need help. When I disassemble a problematic dc-motor due to excessive or premature carbon brush wear, I see scratches / friction traces on the permanent magnets (2x, both magnets have these traces) that looks like the armature iron lamellar were in contact or rubbing with permanent magnets. (Actually the distance of armature body to the permanent magnets are due to design too close but there exists anyway an air gap)

Could this friction or contact have an influence on the carbon brushes during operation of DC-motor?
I have tried to provoke the same issue i.e this friction, after some minutes of operation the power supply voltage reduces and current increases extremely but dc-motor continues to turn.

Could you please help me to understand what is happening during this contact and how could this be explained electrically ?

Thanks a lot.

RE: Excessive Carbon Brush Wear


You will receive much better advice and answers to your problem if you post photographs of the commutator,
and any other portion of the motor showing signs of wear. The bore of the permanent magnet frame for example.
In good lighting, hold your camera/slash/phone pointed at the problematic area and "snap" off some pictures.
Post the photos here in your thread... and then we'll all be able to "see" what you're attempting to explain.

And if the motor has a tag, nameplate, sticker, etc. Take a photo of that too!


RE: Excessive Carbon Brush Wear

I don't think the magnets would lose their strength with the rubbing but if they did then the weaker magnetic field would make commutation worse.

RE: Excessive Carbon Brush Wear

Friction will increase the load.
Increased load means increased current.
Increased current means increased brush and commutator heating and wear.

"Why not the best?"
Jimmy Carter

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close