logo

Carbon Brushes In DC Motors – Common Causes Of Fault and How To Prevent Them

Slip Rings, Commutator, Brush Arms, Carbon BrushDC (direct current) motor rewinds and repairs have been one of our specialist services for many years and in our experience, carbon brush wear is one of the most common causes of DC motor failure, alongside carbon dust and commutator surface wear caused by bad contact with the brushes.

Carbon brushes are found in many DC motors and it is essential they are properly maintained and replaced when necessary to ensure optimal performance of motors and reduce the risk of downtime.

What Is The Use Of Carbon Brushes In DC Motors?

The purpose of carbon brushes in DC motors is to reduce wear on the commutator as well as transferring electricity from outside the motor to the centre. Carbon is used because of its self-lubricating properties, this means less wear on the commutator in comparison with brushes made of harder metals such as copper or steel, in addition to this, it is a good conductor.

Carbon brushes aren’t just found in DC motors, they are also found in large slip ring motors, power generators and welding generators as well as smaller domestic items such as washing machines and handheld power tools.

Common Causes Of Carbon Brush Wear In DC Motors

Of the countless DC motors and generators we have repaired due to carbon brush wear, some of the most common reasons for brush failure we encounter are:

  • Brushes being installed incorrectly or the wrong sized brush being fitted
  • Brushes experiencing damage due to electrical underloading or overloading
  • Winding faults
  • Voltage surges to the motor
  • Issues with the commutator – excessive sparking caused by worn brushes
  • Brushes not being shaped to fit arc of commutator

Our inhouse equipment and expert team allows us to diagnose these common issues and carry out repairs or replacements with a quick turnaround time.

What Happens When Carbon Brushes Wear?

Carbon is a soft metal and brushes are designed to wear out over time, the reason a soft metal is used is to reduce the amount of damage caused to the commutator through friction. Often, before a carbon brush starts to wear, you will experience sparking on the commutator – you can read a case study about this issue and its causes here.

Once the carbon brushes are completely worn the motor will begin to underperform before failing – running a motor with worn carbon brushes can result in extensive damage to the motor.

How Can I Extend The Life Of My Carbon Brushes?

The life of a carbon brush is dependent on several psychical factors including, the frequency of use, alignment of brush and pressure settings, in addition to environmental factors including temperature, contamination and humidity. Routine visual inspections for common problems can help identify them before they cause serious damage, if any of the following occur, you should contact a professional to have your motor inspected:

  • Excessive sparking from the commutator when in use
  • Decrease in power from the motor
  • Complete failure of the motor

Effective maintenance is recommended to increase the life span or your carbon brushes and avoid downtime.

Choosing The Right Carbon Brush For Your DC Motor

The selection of the correct carbon brush grade can greatly influence the performance and lifespan of a motor, but selecting the right specification of brush for your motor can be difficult, especially if the previous brushes have failed to perform.

This is why we pride ourselves on our identification process, taking as little as 2/3 working days this process is essential in selecting a suitable size and grade of brush for your motor from our extensive stock to ensure the best from your motor and saving you money in the long run.

Talk To The Experts

If you’re concerned about the performance of your motor, we can carry out an in-house check and offer advice on whether your carbon brushes are installed correctly or if it could be time for a replacement. Give us a call on 0117 955 2481 or fill out a contact form and we’ll get back to you.

Make an Enquiry
close slider




Please tick all that apply: