DC Motor Maintenance: Tackle Brush Issues
DC motors and even brushed AC motors depend on brushes for good uptime and efficiency as they provide the electrical connection between the commutator and the power source. To efficiently and effectively transmit electricity, brushes must always remain in good condition, which equates to having consistent full, flat contact with the commutator. A good maintenance regime for the brushes and commutators is key to ensuring a DC motor achieves a long service life. Still, even with proper care and maintenance, these components experience wear and tear and will eventually need replacement.
Signs that indicate when replacement may be necessary include the brush surface no longer being smooth and shiny and evidence of chipping and cracking. The brush being worn down to a quarter of its original length is another indication, as is the brush pigtail not securely fastening to the brush as it used to, or the brush not fully conforming to the commutator shape.
When it is time to replace the brushes, the motor’s manual should be consulted to verify that the replacement is of the correct dimension, grade, and type. Let us explore the common problems that affect brushes and commutators.
GROOVING
Grooving leaves a slotted and smooth area on the commutator. It is typically caused by contamination and using brushes with the wrong grade or impurities. If this is evident, it is advisable to check whether the type of brush used is correct. Look for signs of contamination, and replace or clean the brushes if necessary.
THREADING
Threading causes fine lines on the commutator’s surface as a result of copper being shifted from the commutator to the brushes and getting embedded in the surface of the brush, ultimately scratching the commutator. Using the wrong type of brush and contamination are also among the potential culprits of threading in DC motors, along with low brush pressure. If threading occurs, first clean the commutator and replace or clean the brushes and put them back with the proper tension.
FLASHOVER
A flashover is essentially a short circuit in a motor’s brushes due to a buildup of copper particles, dirt, and debris between the segments of the commutator. These segments are then shorted together and cause arcing between the brushes. Given how catastrophic flashovers can be, a DC motor must be deep cleaned, especially its commutator, if this ever happens. Often, cleaning the commutator will no longer suffice and a replacement is required. Lastly, the brushes also need to be inspected for damage from the short circuit.
COPPER DRAG
Copper drag occurs when copper particles are dragged to the very edge of commutator segments because of excessive vibration, brushes with insufficient tension, and abrasive brushes. It is critical to address copper drag as soon as it is discovered since the copper buildup in the commutator segments can lead to the armature windings shortcircuiting and can potentially warrant an electric motor rewind. To address this issue, clean off the commutator’s copper flakes and then examine the brushes to see if they are of the proper grade.
CONCLUSION
When comparing DC vs AC electric motors, it is important to note that the maintenance considerations mentioned above primarily apply to DC motors. Because of the importance of brushes in DC motors and the inherent problems that affect them from time to time, regular maintenance is essential to ensure that the issues above do not fly under the radar and cause any long-term damage or catastrophic failure. Moreover, it is also recommended to always have spare brushes on hand should replacement be the only option due to excessive wear or contamination.