Do you like trivia? Me too. Here's a little something you may or may not have known about electronically commutated (EC) motors.
Sturdy advanced plastics are excellent replacement materials for steel and aluminum throughout the motor either as insulation material, structural parts and enclosures. These plastics, like glass-filled nylon resins — the strongest, non-commodity plastic that’s readily available — improve performance in EC refrigeration motors.
We see eight primary reasons why these types of plastics are the perfect material for high-efficiency, electronically commutated motors:
– The major advantage of metals in traditional motors are their thermal properties. Metals are good thermal conductors. This makes them effective at transferring waste heat from the motor to the outside atmosphere. In low efficiency motors, or in high powered motors, this is an important property as large amounts of waste heat must be dissipated. However, in a small, energy-saving EC motor there is very little waste heat, so this property is not important. In fact, for motors of this type, rather than encouraging heat transfer, it can be preferable to minimize it.
+ Using a plastic housing slows the heat transfer. This provides a more stable environment both inside the motor (protecting the bearings and electronics from thermal shocks and extreme low temperatures) and outside the motor (improving temperature control).
– For commercial refrigeration and other low temperature applications, correct material selection is extremely important, as some metals (including most steels) and many plastics become brittle below about -10°C (14°F).
+ Advanced plastics, rated for low temperature use, retain over 80% of their impact strength at -30°C (-22°F). Thermal insulation properties of plastics are also helpful at low temperatures because they allow the motor to warm up, preventing it from being exposed to long periods of vibration while extremely cold.
– Most commonly used metals can tolerate temperatures far above what is encountered in motors. Very few plastics can operate under such extreme temperatures.
+ However, there are a variety of advanced plastics available which will tolerate the temperatures found in electronically commutated motors. Look for grades of plastic that are UL-rated for normal operating temperatures up to 155°C or 311°F (Class F).
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– Aluminum and other metals conduct electricity, which is a major disadvantage as a ground connection is required to maintain safety when metal is used. This poses the risk that if the connection corrodes or is incorrectly fitted, the motor could become unsafe.
+ Using an advanced plastic for housing and rotor hubs allows some EC motors to meet double insulated standards and avoid the need for a ground connection, while keeping installation and maintenance personnel safe.
– Motors hate the constant temperature swings and moisture found in refrigeration systems. Those types of harsh environments lead to corrosion, a frequent culprit in motor failure. In fact, corrosion from temperature swings and moisture can cause even normally non-corrosive metals like aluminum to degrade. Corrosion is made even worse by combining several metals, such as steel laminations and bearings with aluminum housings (known as: electrolytic corrosion).
+ Plastics do not corrode, and since they are electrical insulators they also prevent electrolytic corrosion between metal parts attached to them, avoiding motor failures.
– No one wants to hear a bottle cooler or commercial refrigerator in a convenience or grocery store because of a noisy, vibrating motor. Metals are rigid and vibrate. Combine that with impact with other parts that vibrate and you've got constant noise. Vibration and impact can also cause wear and tear on parts.
+ Plastics are less stiff than metals and have some internal damping. This minimizes the transmission of motor-generated sound and vibration, particularly high frequency noises. It also helps protect internal components from shock and impact.
BONUS: Here's a video we filmed to show how easy it is to reprogram an EC motor. If you go to the 2:25 mark in the video, you'll hear how quiet the motor is when it's running.
+ High operating temperatures mean only fire-retardant grades of engineering plastics can be used in these motors. There are several levels of fire retardance as defined by international standards, the highest are V-0 and 5-V.
+ Most of us think that metals are normally stronger than plastics. However, with modern engineering plastics, the difference can be minimal. For example, glass-reinforced nylons can have a failure stress of over 200MPa, which is similar to the yield strength of common aluminum alloys and cast or wrought irons.
Additional points to remember:
For more information on this topic, check out these prior posts: