Exhaust Fan Motor "Burning Up."

MTW said:
And you tell us previously that it only happens to this fan.
The others run fine. 😉

Seriously if you want better suggestions, you need to submit better data. I wired and serviced industrial ventilation systems for many years. If you think the Easy solution is the next size up hazardous motor, order it done and tell us if it works.
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Hmmm, do I want to please the guys on this Forum, or please a paying Customer? Let me think about it.
 
TwoBlocked said:
please a paying Customer? Let me think about it.
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Take all the time you need. We're just trying to help. Taking care of the problem, would be the focus to me as a contractor.

What the customer had installed is not doing the job, reliably right? You ask if putting in a bigger motor would fix it.?

Given you only gave us, it's hot and hazardous, it's pretty hard to make a judgment call if a motor change would make a reliable difference, it's not something I would condone, without knowing more about the actual conditions and equipment.
When we did these types of projects, we always met at the site and discussed the situations and conditions and banged ideas amongst the design engineers involved.

More than one head on a project usually produced a better end result. If the customer didn't agree, we would pass on doing what they wanted, if we knew up front if that would not fulfill their need or pass any inspection, future liability was always something that was a concern, not just what the customer wanted to pay for.
 
I think first thing that needs done assuming you have sufficient voltage at this motor is to check the ambient temperature (while running) and also make certain it is not overloaded for some reason. Something simple like 3450 RPM motor when it should have been 1725 will cause excessive loading on a fan motor. Class B insulation motor can run at 130C. which is pretty hot, there is higher insulation class for motors though it may not be as easy to find on single phase motors.

At same time you mention hazardous location. Can the classification even handle the temp particularly if class B insulation isn't high enough, or is this fan supposed to move enough air that the temperature shouldn't be that high in the first place? Or I think someone did mention air flow being too little, as in blocked duct or something, that likely puts less load on the motor, but at same time isn't moving the heated air as much and could allow heat accumulation at the motor?
 
Folks, I have the same questions and might have gotten the answers the other day IF I hadn't gone to the wrong compressor station! (Arrrggghhh) The customer specifically asked for a motor with a higher temp rating, so we are looking for one. Yes, of course, the installation needs to be evaluated. For now, I am looking for options assuming that the problem is what the customer believes it is - the environment is too darn hot.

Another option might be to go with a bigger motor and pulley to get more airflow.
 
Maybe I missed this but I assume you measured the operating current while running and compared to FLA nameplate. Could be something binding or blower is simply oversized and motor is underpowered. Also, measuring the temperature in motor location would be nice to know.
 
dkarst said:
Maybe I missed this but I assume you measured the operating current while running and compared to FLA nameplate. Could be something binding or blower is simply oversized and motor is underpowered. Also, measuring the temperature in motor location would be nice to know.
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Nope, I ended up at the wrong compressor site. It also had a bad motor.
 
Finally got to the correct site. Verified it is a Baldor, 230V, single phase, 184T frame, 2 HP, 1750 RPM, Class B insulation, capacitor start, explosion proof. Motor reads open, phase to phase with ordinary ohmmeter (Capacitor does not charge up). Motor also reads grounded on each phase with 500 Volt megger. Temp taken with a temp gun from inside comp room is 150F (65C) at the plenum.

Fan is belt driven. There is no overload protection, just temp protection within the motors themselves. Breaker for two of the fans is 20amps, which is ok. On the third, it is 30amps, which is not ok. Conductors are #10 awg.

The "story" (ahem ...) is that each of the three fan motors in the building take turns "burning up". The latest one sat around in the weather with the pecker head cover off for quite a while. (Don't know if it would matter much as this is a sealed connection box, due to being Class I, Div 2.) So when it finally got wired up, it didn't last long. It was wired up correctly, btw.

So, Class B insulation is rated for 130C. Since the motor will run 40C above ambient, it should be ok up to 90C (195F). Today was cool and damp around 65F. I can see the plenum becoming too hot for the motors, but they are not in the plenum, being a belt system.
 
TwoBlocked said:
Finally got to the correct site. Verified it is a Baldor, 230V, single phase, 184T frame, 2 HP, 1750 RPM, Class B insulation, capacitor start, explosion proof. Motor reads open, phase to phase with ordinary ohmmeter (Capacitor does not charge up). Motor also reads grounded on each phase with 500 Volt megger. Temp taken with a temp gun from inside comp room is 150F (65C) at the plenum.

Fan is belt driven. There is no overload protection, just temp protection within the motors themselves. Breaker for two of the fans is 20amps, which is ok. On the third, it is 30amps, which is not ok. Conductors are #10 awg.

The "story" (ahem ...) is that each of the three fan motors in the building take turns "burning up". The latest one sat around in the weather with the pecker head cover off for quite a while. (Don't know if it would matter much as this is a sealed connection box, due to being Class I, Div 2.) So when it finally got wired up, it didn't last long. It was wired up correctly, btw.

So, Class B insulation is rated for 130C. Since the motor will run 40C above ambient, it should be ok up to 90C (195F). Today was cool and damp around 65F. I can see the plenum becoming too hot for the motors, but they are not in the plenum, being a belt system.
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Did you check running amps? Could very well be overloaded because of wrong blower or wrong pulley ratio (since it is belt driven) plus you mentioned no overload protection so it will attempt to deliver whatever power is required as determined by blower speed and air flow design of things. It will overheat if it takes more than motor rating to deliver that power. If overloaded by say 15% and has 1.15 service factor it maybe will go for pretty long time. If overloaded by say 40 to 50% it might run long enough until everyone forgets about last time it was replaced and then fail again. Some of this may depend on actual amount of usage it does see along with how long it runs when it does run.
 
TwoBlocked said:
No, it's grounded out and open.
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You have other of the same thing that periodically burn out if I recall, maybe check one of those to see what it draws. If too high that is probably why they tend to burn out periodically. If so you need to evaluate whether bigger motor is needed or if you can slow the fan down (or even just put some restriction in the air flow) to reduce load and yet still move enough air to do what needs done.
 
ptonsparky said:
More than one motor burnt up because incorrect belt tension, esp when they try to speed things up with new pulley ratios.
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I agree. Doesn't take much increase in speed to require twice the motor to run it in most cases.

Too much belt tension takes out the bearings which can also lead to overheating the motor or even lead to rotor contacting stator.
 
Huh? The nameplate says 40C above ambient:

1750112770179.png

But the performance sheet says 70C rise at full load:

1750112691745.png

Oh, I see! I misunderstood. This motor is not rated to be in an ambient temp of greater than 40C (105F). Yep, that's a problem!!!
 
40C is just the basic test standard for motor FLC ratings and thermal damage, call it the "minimum". You can absolutely get better insulation ratings, Class B insulation is actually kind of the lowest (Class A is lower, but I don't think anyone makes Class A insulation any more). You should be looking for a motor with AT LEAST Class F insulation, Class H would be better. Both of those are available, but not likely "off the shelf", so you will have to order them and wait, then they should probably have a spare on hand because of that.

Temperature-limits-555x360.jpg
 
Jraef said:
40C is just the basic test standard for motor FLC ratings and thermal damage, call it the "minimum". You can absolutely get better insulation ratings, Class B insulation is actually kind of the lowest (Class A is lower, but I don't think anyone makes Class A insulation any more). You should be looking for a motor with AT LEAST Class F insulation, Class H would be better. Both of those are available, but not likely "off the shelf", so you will have to order them and wait, then they should probably have a spare on hand because of that.

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For single phase motors, I have only seen Class B. Custom made motors? Not gonna happen for this customer. Am thinking the best path is to mess with the pulley sizes and strive for 80% of FLA.
 
TwoBlocked said:
For single phase motors, I have only seen Class B. Custom made motors? Not gonna happen for this customer. Am thinking the best path is to mess with the pulley sizes and strive for 80% of FLA.
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Reduction in air flow will increase the ambient temperature even more. Some thermal engineering calculations need to be done.
 
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