Motor keeps tripping internal overloads

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AC\DC

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Installed new motor was grinding and tripping overloads. Found the grinding fix the issue spins free now.
But now it won’t stay on longer than 10 minutes. It’s an exhaust fan for a kitchen and I is extremely hot in the motor area. I am waiting for overloads to reset. Then take a amp reading.
While I am sitting waiting I wondering.
They normally turn i on in the morning when nothing is hot yet and fan keeps it cool .

now it’s hot and it keep tripping ,could them not letting it normaly getting as warm as it is now allow it to run vs trying to start it when it’s like 140 when it’s trying to start now.
 
I wondering if that is a smaller motor than originally there. There is another exhaust hood next to it and it’s about half its size. It no longer is functioning and no motor.They might of took out and installed in here
 
I can’t find anything wrong, wondering if either the motor is undersized or the vent needs cleaning and barring need lube, to much drag on motor
.
No tag of manufacture to call about unit.

must be mechanical it draws 5.8 when not connected to belt.
 
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Most of those fans have an adjustable pulley. You loosen a set screw and change the distance between the plates on the pulley which effectively changes the pulley's diameter. This can alter the rpm's of the fan enough to lower the load on the fan motor.
 
Thanks for responding. I looked, though I will look again tomorrow. the unit is about 70 years old its original.
This motor can't be the original one though. Now that I am thinking about it and looking at this picture. It was originally wired for 240, He had a tweakier install the Previous one so I am wondering If that is the problem, he got the wrong motor?
 

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ActionDave said:
Most of those fans have an adjustable pulley. You loosen a set screw and change the distance between the plates on the pulley which effectively changes the pulley's diameter. This can alter the rpm's of the fan enough to lower the load on the fan motor.
Click to expand...

Yup though it doesn't look like the motor pulley is adjustable on what you have. Probably some jack leg just replaced it with a regular pulley. You are going to have to "make it so". Any HVAC supply or Grainger will have what you need. You may have to get a couple of sizes just to make sure you can get it where you want it. Oh, and don't forget a shorter belt if you don't have the adjustment range.

If you have to slow it down too much in order to bring that motor's current draw down to where it should be you'll know you need a bigger motor. But I suspect that 1/2 horse is OK.

Something else you might want to check is the condition of the duct work and grease filters to see if it can create a proper air flow. (I don't remember if a blocked intake will cause more of a load on the motor.)

-Hal
 
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hbiss said:
If you have to slow it down too much in order to bring that motor's current draw down to where it should be you'll know you need a bigger motor. But I suspect that 1/2 horse is OK.
-Hal
Click to expand...
Would my problem be the drag I am having on the load end of the motor, slowing the motor down would increase the current?
I dive into the pulley idea thank you for that.
hbiss said:
Something else you might want to check is the condition of the duct work and grease filters to see if it can create a proper air flow. (I don't remember if a blocked intake will cause more of a load on the motor.)

-Hal
Click to expand...
Ya I was thinking that may be an issue, he said it was just clean, but I don’t believe from the Greece that was Ozzie onto the roof.
 
Can you uncouple the motor from the fan pulley or linkage completely and then run it under no load? Then take an amp reading. It should be significantly less than full load if the motor is good. Help you determine if it’s a motor issue or fan/drive linkage issue.
 
AC\DC said:
I can’t find anything wrong, wondering if either the motor is undersized or the vent needs cleaning and barring need lube, to much drag on motor
.
No tag of manufacture to call about unit.

must be mechanical it draws 5.8 when not connected to belt.
Click to expand...
That may be the problem, they installed the wrong hp, or wrong size pulley. You can get an adjustable sheeve pulley, but if it’s the wrong hp to begin with, the air flow may not be sufficient. You may be able to cross reference the specs with a new fan, to see if the rpm, hp, and cfm is similar.
 
I see three possibilities:

1. The original motor was 3/4 HP

2. The original motor was 6 pole

3. An incorrect pulley was installed when the motor was changed. (Maybe the replacement motor had a different shaft size and he just got “something close” that would fit the new shaft.
 
hbiss said:
Yup though it doesn't look like the motor pulley is adjustable on what you have. Probably some jack leg just replaced it with a regular pulley. You are going to have to "make it so". Any HVAC supply or Grainger will have what you need. You may have to get a couple of sizes just to make sure you can get it where you want it. Oh, and don't forget a shorter belt if you don't have the adjustment range.

If you have to slow it down too much in order to bring that motor's current draw down to where it should be you'll know you need a bigger motor. But I suspect that 1/2 horse is OK.

Something else you might want to check is the condition of the duct work and grease filters to see if it can create a proper air flow. (I don't remember if a blocked intake will cause more of a load on the motor.)

-Hal
Click to expand...
For a fan or centrifugal blower a blocked intake will reduce the load on the motor. For an axial fan though (not the OP's problem) the reduced airflow may still cause the motor to overheat.
 
MattG0311 said:
Can you uncouple the motor from the fan pulley or linkage completely and then run it under no load? Then take an amp reading. It should be significantly less than full load if the motor is good. Help you determine if it’s a motor issue or fan/drive linkage issue.
Click to expand...
It’s drawing 5.8 uncoupled. 10.34 when coupled. Thank you guys for the help at least I have some ground to stand on now at least for my comfort zone.
 
In a centrifugal fan, Load = Flow. If the fan was designed for a certain flow and someone tried to get more flow somehow, they OFTEN have no clue as to the effect on the motor load, they just don't understand it well enough. So they could have changed the sheave, they could have changed the motor, they could have changed the motor speed, they could have changed the fan blade pitch, they could have removed a damper, you just can't troubleshoot your way out of this without a detailed history and you don't have that. It just needs to be replaced, and an ME needs to pick the right fan for the application as they want it now.
 
AC\DC said:
Would my problem be the drag I am having on the load end of the motor, slowing the motor down would increase the current
Click to expand...
No. You are not slowing down the motor by using a smaller sheave on the motor shaft. You are slowing down the blower wheel putting less of a load on the motor! I would try a smaller adjustable sheave on the motor shaft and get it down to the allowable current draw to just to see what happens. Only a few dollars and I wouldn't go any further.

Jraef said:
It just needs to be replaced, and an ME needs to pick the right fan for the application as they want it now.
Click to expand...

I agree.

This actually would be a job for a HVAC or kitchen hood guy. But my gut is just from looking at it since this has been there so long and from the condition it's in, I'll bet the owner isn't going to want to spend any money on it. Don't even want to know what the grease filters look like.

-Hal
 
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