Will shutting on and off a continuous duty motor shorten its life?

Question

One of my ongoing projects is to save electricity costs at my plant. We have several continuous-duty electric motors used to run things like conveyor belts. My question is, would shutting those motors on and off (ie: on for 20 days, off for 20 days) appreciably shorten the motor's life? I need to know if the plant would save any money by using less electricity, versus the replacement cost of the motors. Thanks.

Answer 1

You are not shortening the motor life with such a long period of off time. Short cycling with multiple (> 6)starts in an hour could cause heat build up and is considered bad for the motor.

If the motors are in a damp environment it is usually a good practice to keep the motor warm with a heater or heat lamp to prevent moisture from degrading teh motor insulation. Some larger motor have a built in heater that it turned on when the motor is stopped.

20 day on/off cycles: It is considered good practice to alternate te use of duplicat equipment to even out wear between the units. This gives ample time to service the off duty equipment and repair it should the need arise.

Answer 2

A history of failure with a specific motor might tell you something right off the bat. Factor in the quality and reputation of the manufacturer first. If the particular motors are used within specs, it should last a long time. Other than numerous abrupt starts and stops under heavy load, it is unlikely this practice will shorten the life of a motor.The specific size and type of motors also needs factored in too. Company's lay out more money these days for energy. I'd draw up a proposal with estimated costs savings and submit it for review. If an additional layer of managing this process is needed, factor that in too. You might want to consider replacing overhead lighting if your using older fluorescent. Newer high efficiency lighting using reflectors saves money, and usually comes with tax rebates as well.

Answer 3

The motor should be generally okay if it is not shut off or started under loaded conditions- or cycled quickly. If your control scheme includes a time delay of at least 30 seconds or 1 minute, cycling should not be a problem.

In my experience, it seems to be a better strategy to install variable frequency frives VFDs for slowing and speeding up converyors instead of stopping and starting. These things are expensive but can really save big bucks on large motors. The larger the motor, the greater the savings.

Answer 4

Every man made device has a limited amount of cycles. depending on the design of the motor and rate it heated and cooled, your application sounds to be not deleterious.