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I have two vent hood blowers I got out of a commercial kitchen years ago. They each have two squirrel cages with the motor in the middle. They are in a housing with a transitional duct that turns rectangular. They move alot of air. And I mean alot. I put them in the back of the shop in front of a window and blow shaded air through the shop out the front.
The motors are GE. They are 3 amp. I put a meter on them yesterday and they were pulling 2.3 or so. I stopped and started one and it jumped up to 3 amps and then back to 2.3 or so.
After the motors run, they are very warm. I don't know why. Is it normal for them to be very warm? I can stick my finger through the housing and touch the motor and it's hot after it runs a while.
The cords are not warm. They are on a 20amp circuit. They are the only thing on that circuit.
Is there any thing I can or should do?
Thanks
RP
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08-14-2018, 03:01 PM
(This post was last modified: 08-14-2018, 03:06 PM by TDKPE.)
Is there an insulation class on the motor's nameplate (A, B, F, or H)? Class A insulation, which is the lowest at 105C/221F, has an allowable motor temperature rise of 60C/108F above ambient (assumes a 40C/104F ambient). Even allowing a large temperature difference between the internal winding temperature and the outside frame temperature, that's potentially hot to burning hot. And that's the lowest insulation class.
It's normal. Just be sure the current draw is less than the nameplate, and all else will fall into line.
Oh, and I'm assuming it's a continuous-duty rated motor. It will say so on the nameplate. Something like "Time Rating: Cont." I can't imagine a fan or blower that isn't.
Tom
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Could the original ducting caused air to flow across motor to cool it?
I've got a smaller version of that in my shop. It was in a residential stove from the '60s.
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Wild Turkey
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(08-14-2018, 03:01 PM)TDKPE Wrote: Is there an insulation class on the motor's nameplate (A, B, F, or H)? Class A insulation, which is the lowest at 105C/221F, has an allowable motor temperature rise of 60C/108F above ambient (assumes a 40C/104F ambient). Even allowing a large temperature difference between the internal winding temperature and the outside frame temperature, that's potentially hot to burning hot. And that's the lowest insulation class.
It's normal. Just be sure the current draw is less than the nameplate, and all else will fall into line.
Oh, and I'm assuming it's a continuous-duty rated motor. It will say so on the nameplate. Something like "Time Rating: Cont." I can't imagine a fan or blower that isn't.
Disassembly is required to see the name plate. I already put it back together.
Thanks for your expertise.
RP
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(08-14-2018, 03:24 PM)Wild Turkey Wrote: Could the original ducting caused air to flow across motor to cool it?
I've got a smaller version of that in my shop. It was in a residential stove from the '60s.
No. The squirrel cages are isolated from the motor. The motor is in the middle with the shaft going out of both ends of the motor to the cages. There is also a housing over the motor. So I don't think much airflow got to the motor.
Thanks for your input.
RP
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I've had squirrel cage fans that overheat when they don't have enough air restriction on the outflow. Still not sure why but it happens. Try restricting the air flow.
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(08-21-2018, 07:51 PM)Eurekan Wrote: I've had squirrel cage fans that overheat when they don't have enough air restriction on the outflow. Still not sure why but it happens. Try restricting the air flow.
If the motor overheats and restricting the airflow helps then it's because the motor is working too hard moving more air than it was designed to move.
Same thing with a vacuum cleaner -- when you cover the end of the hose the motor sounds like it's working harder when it's actually not working much at all because it's not moving any air. Kind of counter-intuitive but that's the way it is with motors and air.
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Blowers are designed for static pressure for the ducting they are designed for. Running wide open, they cavitate then grab sudden pulses of air. The motor will slow, over amp and run hot.
Connect it to duct system or block the supply air until it settles down. You will probably feel and hear the air flowing steady and settling down. The motor will increase in speed and the amps will fall.
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(08-21-2018, 07:51 PM)Eurekan Wrote: I've had squirrel cage fans that overheat when they don't have enough air restriction on the outflow. Still not sure why but it happens. Try restricting the air flow.
Centrifugal pumps work the same way; you can regulate the flow, and by extension the power, by partially or completely blocking the in- or out-flow. But axial fans and pumps (like boat propellers) are the opposite, and increasing the flow restriction will increase the required input power for a constant impeller speed.
Blocking the inlet or outlet of a centrifugal blower causes the air in the scroll to simply spin around with the impeller wheel, and that doesn't take much power (other than friction) compared to accelerating that air stream and raising its static pressure from the inlet to the outlet.
Tom
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(08-22-2018, 05:38 PM)TDKPE Wrote: Centrifugal pumps work the same way; you can regulate the flow, and by extension the power, by partially or completely blocking the in- or out-flow. But axial fans and pumps (like boat propellers) are the opposite, and increasing the flow restriction will increase the required input power for a constant impeller speed.
Blocking the inlet or outlet of a centrifugal blower causes the air in the scroll to simply spin around with the impeller wheel, and that doesn't take much power (other than friction) compared to accelerating that air stream and raising its static pressure from the inlet to the outlet.
Okay,
I'll try restricting the blowers a little and see what happens.
Thanks for all your inputs.
RP
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