Why Motors Fail: Part 4 – The Top 5 Electrical Failures in DC Motors - HECO

While AC motors dominate the conversation in many industrial settings, DC motors are indispensable in applications requiring precise speed control and high torque. However, they come with their own set of challenges.

Based on HECO’s field data collected from more than 240 clients within our TracRat Equipment Management software, five recurring electrical failure modes for DC motors stand out, each with the potential to cause significant disruptions if not proactively addressed.

In this post, we’ll explore these common DC motor electrical failures, discuss their symptoms, and provide actionable solutions to keep your equipment running smoothly.

To learn about our data collection, findings, and suggestions to keep your motors from failing, read Part 1 – The Top 5 Failure Modes for AC and DC Motors, Part 2 – Avoid the Hidden Costs of Misalignment, Lubrication Issues, and Shaft Voltage, and Part 3 – The Top 5 Electrical Failures in AC Motors.

Commutator Wear: A Gradual Decline

The commutator is the heart of a DC motor, responsible for transferring electrical current to the windings via brushes. Over time, wear and environmental factors take their toll.

Issues often present as:

• Grooves or scoring on the commutator surface.
• Visible arcing or sparking during operation.
• Poor motor performance or uneven speed control.

To avoid excessive wear, inefficient power transfer, overheating, and eventual motor failure, ensure regular inspection and maintenance of commutators, including:

• Proper turning and undercutting during repairs.
• Using brushes made from the correct grade of material to minimize wear.
• Keep the operating environment free from dust and contaminants.

Brush Holder Issues: An Overlooked Threat

Brush holders themselves are critical for maintaining proper contact between brushes and the commutator, but they often suffer from neglect.

These issues often present as uneven or rapid brush wear, loose or misaligned brushes, and carbon buildup or tracking in the brush holder.

Improper brush tension or alignment can lead to:

• Excessive heat.
• Premature brush failure.
• Potential damage to the commutator.

Conducting periodic inspections to ensure proper spring tension and alignment can drastically reduce these issues. Be sure to clean brush holders regularly and replace worn components to maintain consistent contact and minimize wear.

Overloading and Stalling: Asking Too Much

DC motors are particularly vulnerable to overload conditions, often resulting from operational demands exceeding the motor’s rated capacity.

These issues often present as:

• Flat spots on the commutator.
• Overheated components with discoloration or burning.
• Reduced motor efficiency or outright stalling.

Prolonged overloading stresses the windings and commutator, leading to insulation breakdown and short circuits.

To avoid these issues, match motor capacity to operational demands during the design phase. Install overload protection devices and regularly monitor operating conditions to ensure the motor isn’t pushed beyond its limits.

Grounded Fields and Interpoles: A Short Path to Failure

Moisture, contaminants, or physical damage can compromise the insulation on DC motor fields or interpoles, leading to grounding faults.

Difficulty starting the motor, erratic operation, tripped circuit breakers or blown fuses, and burned or charred insulation on the field windings are all signs of a grounding fault.

To avoid disabling the motor and causing extensive damage to connected electrical systems:

• Store motors in dry, temperature-controlled environments.
• When in operation, use protective enclosures to guard against contaminants.
• Implement routine insulation resistance testing to detect early signs of deterioration.

Poor Ventilation and Overheating: A Universal Problem

Like their AC counterparts, DC motors are highly susceptible to ventilation issues, which can exacerbate other failure modes.

A lack of ventilation often presents as:

• Hot motor casings and components.
• Blocked or obstructed cooling pathways.
• Reduced motor performance or frequent trips due to thermal overloads.

As a result, excessive heat accelerates insulation deterioration and increases wear on critical components.

To avoid ventilation issues and overheating, keep ventilation systems clean and operational. Install motors in well-ventilated locations and ensure cooling fans are functioning properly. Use predictive maintenance tools to identify overheating trends before they lead to failure.

All Systems Go

DC motors play a crucial role in many industrial processes, but their reliability hinges on proactive maintenance and a thorough understanding of common failure modes. At HECO, our team not only repairs DC motors but also provides insights and strategies to prevent future failures.

Ready to maximize the lifespan and performance of your DC motors? Contact us to learn how HECO’s expertise and TracRat software can enhance your equipment reliability.

Posted in Equipment Management, Repair