Factors In Motor Life Expectancy

 

“How long will my motor last?” is the age-old question is at the heart of every motor purchase.

Most of the time, it’s almost impossible to accurately predict motor life. Every application presents a unique set of circumstances for an electric motor. But, there are key factors that play an important role in motor life expectancy. Keeping these factors in mind can help you identify and recognize signs signaling the end of your motor's lifespan.

How Applications Affect Life Expectancy

Every application presents a specific set of circumstances for a motor. These circumstances that can impact the longevity of your motor. Paying attention to these factors can help you get the most out of your motor and understand why some motors last longer than others.

Frequent Starts and Stops

Capacitor starts are engineered to deliver around 500,000 starts for a motor. The number of across-the-line starts affects the life of a motor. In applications requiring frequent starts and stops, motors often run the risk of capacitor failure. The good news? You can replace capacitors within the motor. But until you replace the capacitor, the motor will be inoperable. Because of this, keep across-the-line starts to a minimum. Also, familiarize yourself with the NEMA guidelines for Number of Starts. You can find those at NEMA MG1-12.54. These guidelines can help you estimate the insulation life of your motor.

Motor Sizing

Motors of the incorrect size for their applications will instinctively have shorter lives. This can create issues related to operational factors like torque, speed, and horsepower. These issues can lead the motor to run hotter or experience an overload.

Radial (Overhung) and Axial (Thrust) Load

The amount of force applied to the motor shaft affects how rigid the shaft needs to be. It also impacts the bearings. If your motor application involves high radial or axial loads, choose bearings that can handle the extra force.

Environment And Life Expectancy

Make sure your motor enclosure is appropriate for the application environment. Environmental factors (and how to mitigate them) include:

• Ambient temperature: Keep between  0°C and 40°C.
• Elevation: Install at 3300 feet or less.
• Motor ventilation: Do not obstruct ventilation.
• Mechanical shock and vibration: Keep to a minimal level.

Each environment, factory, and business is different. Consider the following to determine whether you have the right motor type or configuration.

Industry Needs

Depending on the industry, one motor can operate in many configurations and scheduled cycles. Factors in different industries affect a motor's life. For example, farm and agriculture industry motors tend to turn over much faster than a standard garage door motor. That's because of increased dust, dirt, and moisture found in these environments.

Moisture-Prone Environments

Not all motors are designed the same. Ingress Protection ratings will give you an idea of what type of environment a motor can handle. Ensuring proper insulation and protection is essential to the longevity of any motor. High-moisture or humidity environments present the following issues that can lessen motor life:

• Rust buildup within a motor can become a problem for the windings and rotor shaft. With enough buildup, a motor will eventually lock up. This will lead to some of the most integral components within the motor breaking.
• Insulation breakdown caused by moisture can lead to a higher motor temperature. The disproportionate ratio between conductors and insulators causes increased temperatures. Motor can harm the internal windings and rotor but also erode bearing grease. The warmer the motor runs, the faster grease in the pre-lubricated bearings tends to wear.
• Electricity and water are a chaotic pairing. Hardly anything good comes out of their interaction (unless the motor can operate in washdown environments). As a conductor of electricity, water creates several concerns. Combining water and electricity can not only hurt a motor, but more importantly, those working nearby.

Ventilation

Airflow and cooling can determine if a motor's internal components can operate in certain environments. Some motors can maintain their own cooling temperature regulation. Others will need to be within an application's airflow. Considering features like enclosure design or insulation materials will give you an idea of where to place a motor.

Motor Operation

External factors may impact a motor's internal components. Yet, internal components will pose their own threats to motor longevity over time. Engineers have more confidence predicting life expectancy when a motor operates under ideal conditions. Here are the manufacturer-designed specifications engineers consider:

Bearing Maintenance

Bearings are one of the most important components of a motor. Along with pre-lubricated grease, bearings play an important role in ensuring proper operation. Users need to:

• Lubricate motor bearings per IOM published guidelines.
• Keep water and contaminants to a minimum.
• Control bearing loads to provide a minimum B-10 life of 25,000 hours.
• Replace bearings periodically to prevent permanent motor damage.
• Limit shaft voltages (caused by unbalanced line voltage or operation from inverter power) to 0.5 volts peak. .

Temperature and contaminants that get into the bearing will shorten grease life. Factors like motor environment play a huge role in how warm or cool the motor runs. These factors directly impact the efficiency of the grease.

Bearing failure is a high-risk concern for any motor. Bearing failure will lead to issues like rotor strikes, shaft erosion and lockups. These issues will render the motor inoperable and lead to replacement.

Supply Voltage and Frequency

NEMA MG1-12.44.1 stipulates that motors must tolerate +-10% voltage variation and +-5% frequency variation. However, users should operate a motor at nameplate voltage and frequency for optimum life.

• Supply source voltage waveforms should be sinusoidal, balanced within 1%, per NEMA MG1-12.45, with rising times greater than 2 milliseconds and contain less than 2% total harmonic voltage distortion (typical of ‘clean’ utility power). This reduces turn-to-turn, coil-to-coil, and phase-to-ground voltage stress and prolongs motor insulation life. Equip hard-switching solid-state inverters with output-side inductive filters with >5% impedance. This will provide a comparable waveform..

Service Factor

Just because a motor lists a certain horsepower (HP) doesn’t mean it only operates within that specific HP. Specifications like service factor (SF) indicate the range and maximum limit a motor can tolerate. For example, a 2 HP motor that has a service factor of 1.5 is technically capable of operating at 3 HP (2 HP x 1.5 SF = 3 THP). Yet, that doesn’t mean the motor should operate at a 3HP capacity. Doing so places more stress on the motor than it was designed to tolerate. In turn, this will reduce the motor's lifetime compared to if it had been running at 2 HP.

Resources to Help Predict Life Expectancy

To get the most accurate estimate of motor life expectancy, make sure the motor is suited to both the environment and the application it powers. Engineers can only design motors for a limited number of specific uses. If you have a specialized or unique application, consider a custom design.

You can find information on getting the most out of your motor by reviewing a motor's nameplate or supplied operation manual. You can also check out the Regal Rexnord Electric Motors section for resources to get the best output of your motor. For questions about motor life expectancy, finding a solution that meets your application and industry needs, and how to get the most out of your motor, contact our experts below.