Amid another bitter cold winter, operators need to take a careful look at their electric motor safety and operation. Typically, industrial motors have a robust service temperature range: -20° C to 40° C is common for industrial motors. This means they can be operated in cold environments except on the coldest of winter days.

With the growth of electric vehicles (EVs), this will be a growing concern for many vehicle owners. However, EVs are more likely to suffer battery power or capacity challenges than motor performance issues.

Surprisingly, one of the most prominent risks to motors in cold weather is overheating. This, along with considering a few other risk factors, should keep a DC or AC motor reliable after a chilly season.

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Overheating

Although the ambient temperature certainly helps exhaust waste heat from an electric motor, the accumulation of ice and snow can actually cause the motor to overheat. In many cases, the ice and snow act as an insulator and prevent the motor from removing heat via ventilation ports.

This can be exacerbated for explosion-proof designs, which have carefully designed ventilation systems to dampen internal fires but are also more susceptible to obstruction. In addition, compressive pressure for combustible gases are higher in cold temperatures, meaning it is even more important to ensure adequate ventilation.

Condensation

In many locations, an outdoor electric motor will be exposed to numerous precipitation, freeze and thaw events in a winter season. The dynamic weather and humidity levels, along with the motor's own thermal cycling, will likely draw moisture into the motor enclosure over time. This can be addressed with a drain plug, which should be pulled periodically to allow moisture to escape. Even totally-enclosed motors will likely have some moisture ingress. For installations that will need to work on demand in nearly any temperature, an integral space heater can ensure the motor enclosure maintains low humidity.

Demagnetization

Unless operating in tundra or arctic conditions, most electric motors won't have to deal with potential demagnetization. As the temperature drops, ferrite-based permanent magnet motors will actually begin to temporarily lose the strength of their magnetic field. Permanent demagnetization does not begin until -60° C.

This affects the ability of the motor to provide its rated torque or RPM and it is more pronounced in low-torque, low-speed applications. The effect is relatively minor, typically costing less than 10% in efficiency or performance, and is reversible. And this only is relevant to ferrite magnets; other types of magnets typically develop a stronger field at low temperature.

Lubrication and materials

If the motor will be laid up for most of the season, it is important to regularly rotate the motor shaft so lubrication is distributed throughout the bearings and other wear components. This can be as simple as hand-turning the shaft a few times per week. Bearings laden with grease may need a special winter formulation to increase lubricant viscosity. Oil bearings will require an integral heater or pump. Failure to address lubrication during cold duty cycles can create overheating.

There are other materials used in the motor enclosure or assembly that create vulnerabilities for the machinery. Seals are typically a natural or manufactured rubber which inevitably become brittle or weak once exposed to multiple thermal cycles, chemicals, UV and moisture. Seals are a mechanical, consumable component that need to be exchanged on regular preventative routines.

Similarly, certain plastics will fail with age and repeated exposure to contaminants and mechanical or thermal stress. This can affect fans, brackets, wire insulation and a number of other components. The best practice is to regularly inspect these materials for signs of wear or fatigue.

[Learn more about AC motors on GlobalSpec.]

Summary

Electric motors are durable pieces of equipment and their immense utility means that many face the cold climes of winter. For the most part, the motors will run reliably throughout winter or once recommissioned in the spring. However, operators should consider some of these key challenges to ensure the maximum service life from their electric motor.

Reach out to a DC motor or AC motor manufacturer for specialty applications or to learn more about protecting electric motors in icy weather.

To contact the author of this article, email kharrigan@globalspec.com