Ask Dr. Nick: Any Suggestions for an Overheating Hoist?

Question: We are having issues with overheating Hoist. We are using a 2ton electric 208~230V, temperature in the area will reach to 110-125. Any suggestions?

Dr. Nick: I’ll try to give you some immediate pointers, but you probably need to approach a specialist hoist manufacturer before you implement any major alterations.

Anyone who has ever worked at an elevated position in a rotomolding plant will have experienced how the ambient temperature increases dramatically as you get nearer to the roof of the building.  Hot air rises and accumulates.  Even with good ventilation, rotomolding machines generate a lot of waste heat and this tends to rise upwards and concentrate at higher elevations.

Depending on the class of motor being used in your hoist, its insulation starts to break down at an accelerated rate above 220 to 356°F.  Your recorded ambient temperature is 110-125°F, so, why is there a problem?  The answer lies in how your motor is designed to cool itself.

Systems vary, but most motor enclosures are designed to provide sufficient cooling to keep the hottest parts of the motor below the maximum temperature for its insulation class — assuming ambient air at or below about 100°F.  Your factory conditions are creating an ambient condition above this, so motor cooling will be impaired to some extent.

Possible things you can try, to alleviate the condition, include:

1. Reduce the local ambient air temperature by drawing in colder air from outside.  This may be relatively easy (eg opening a nearby building vent), or may get complicated and expensive.
2. Increase the flow of air over the motor enclosure by installing an additional fan near to the hoist motor’s resting location.  This fan could be triggered to initiate via a thermocouple set at (say) 85°F, so that you don’t waste fan power when the ambient conditions are more favorable.
3. Uprate the motor horsepower.  Motors designed to work in continuously hot environments are often downrated (ie their assumed effective horsepower is reduced).  Incidentally, downrating is also recommended for high-elevation locations. NEMA (National Electrical Manufacturers Association) codes have tables of suggested down-rating requirements.  For example, the recommended down-rating for an ambient of 125°F would be 20%, for elevations up to 3,000 ft.
4. Don’t overlook lubrication of all parts of the system.  An elevated ambient temperature will tend to dry out many lubricants and greases, making them less effective.  It may help to lubricate critical parts more frequently.

Hopefully some of these general suggestions will mitigate your problems, but a specialist supplier of hoists and electric motors should be able to provide more specific help.

Dr. Nick Henwood is the Technical Director for the Association of Rotational Molders. He has 30+ years of experience in rotomolding, specializing in materials development and process control. In 2022 he was inducted into the Rotational Molding Hall of Fame. He operates as a consultant, researcher and educator through his own company, Rotomotive Limited, based in UK.