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. Thus, 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 regimen for the brushes and commutators is key to ensuring your 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.
The following signs are a good indication as to when that may be necessary:
- The brush surface is no longer smooth and shiny
- The brush surface shows chipping and cracking
- The brush has become worn down to a quarter of its original length
- The brush pigtail does not securely fasten to the brush as it used to
- The brush shape does not fully conform to the commutator shape
When it is time to replace the brushes, consult the manual to verify that the replacement is of the correct dimension, grade, and type for your DC motor. With that said, let us explore the common problems that affect brushes and commutators.
1. 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. Thus, check whether the type of brush used is correct, look for signs of contamination when grooving is present on the commutator, and replace or clean the brushes if necessary.
2. 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.
3. 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 it ever happens. Often, cleaning the commutator will no longer suffice and require a replacement. Lastly, the brushes also need to be inspected for damage from the short circuit.
4. Copper drag
Copper drag occurs when copper particles are scrapped 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 short-circuiting and 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’s 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.
In the event that your DC motor fails, you will need the help of trained professionals to restore it back to OEM standards. By engaging with a trusted electrical engineering company in Singapore, you can rest assured that your critical machinery, from electric motors to generators and transformers, is in good hands and will be as good as new in no time.