Thermal protection on Air Circ Motor

[fifty60]

I have a .17HP single phase motor that I am trying to run at 115V 50hz. This motor is rated for 115V 50/60Hz. I do not completely understand why I do not have to derate the voltage at 50Hz instead of keeping the 115V for 50 and 60Hz, but the motor manufacturer says that lowering the voltage will make the motor run hotter at 50Hz.

The motor is an air circulator for an oven. At extremely hot temperatures, and at 115V 50Hz, the motor occasionally drops out due to the thermal protection. The only thing I can think to do is to equip a biscuit fan on the enclosure to keep the ambient around the motor cooler. Is there anything else that I can do to draw the heat away from the motor?

The shaft and fan blades are inside the oven, and the motor housing is outside the oven. The motor is an open air cooled motor. It is drawing rated amps which means it should be at 75% full load. there is a vented enclosure added to around the motor, but it is not part of the motor.

Can I do anything with a heat sink or are there any other remedies available for this?

 

[GoldDigger]

I have a .17HP single phase motor that I am trying to run at 115V 50hz. This motor is rated for 115V 50/60Hz. I do not completely understand why I do not have to derate the voltage at 50Hz instead of keeping the 115V for 50 and 60Hz, but the motor manufacturer says that lowering the voltage will make the motor run hotter at 50Hz.

The motor is an air circulator for an oven. At extremely hot temperatures, and at 115V 50Hz, the motor occasionally drops out due to the thermal protection. The only thing I can think to do is to equip a biscuit fan on the enclosure to keep the ambient around the motor cooler. Is there anything else that I can do to draw the heat away from the motor?

The shaft and fan blades are inside the oven, and the motor housing is outside the oven. The motor is an open air cooled motor. It is drawing rated amps which means it should be at 75% full load. there is a vented enclosure added to around the motor, but it is not part of the motor.

Can I do anything with a heat sink or are there any other remedies available for this?

If there is no motor shaft available on the outside to connect a fan to, the best alternative would be the separate fan as you suggest.
A heat sink would have an unpredictable effect on heat transfer from the open motor and should not be relied on IMHO.
The last thing you want to do is cool the thermal protection but not the motor windings.

 

[fifty60]

The motor is not drawing more than the rated amps. The heat is coming from the top of the oven. I need something to insulate the motor housing and enclosure from the heat coming through the top of the oven. Can heat travel from the inside of the oven to the inside of my motor through the shaft of the motor?

 

[GoldDigger]

The motor is not drawing more than the rated amps. The heat is coming from the top of the oven. I need something to insulate the motor housing and enclosure from the heat coming through the top of the oven.

If the freely circulating air temp around the motor enclosure is low, then yes, something to slow down any heat transfer from the over might help.

Some will be coming in through the motor shaft and the motor mounting bolts. Hard to see a good way to insulate those without looking at the motor in more detail.
If it is radiated heat, a simple shiny metal or foil heat shield with air circulation on both sides might be enough to do the job. Like one of the double layer baking sheets, for example.

 

[fifty60]

Wouldn't the heat in this situation always be conduction or convection? Conduction through directly connected parts and convection from the interaction between the heated parts and the air in the enclosure?

 

[kwired]

I have a .17HP single phase motor that I am trying to run at 115V 50hz. This motor is rated for 115V 50/60Hz. I do not completely understand why I do not have to derate the voltage at 50Hz instead of keeping the 115V for 50 and 60Hz, but the motor manufacturer says that lowering the voltage will make the motor run hotter at 50Hz.

What kind of motor is it? My guess is either shaded pole or PSC. Either one of those will handle voltage or frequency changes better then other induction motor types will.

 

[mgookin]

...

. The motor is an open air cooled motor. ... there is a vented enclosure added to around the motor, but it is not part of the motor.

...

Can you operate the system without that vented enclosure to see how it performs?

I'm wondering if that enclosure is obstructing the airflow to the extent it's contributing to, or causing, your problem.

Maybe put a thermocouple in there with the cover on until failure, then remove the cover and let it cool to ambient, run it without the cover, and see the difference. Maybe your vented cover needs to be more open, like maybe a screen or welded wire cage.