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Down at the fish plant they have several drive-in blast freezers. One of the smaller ones has two big evaporator fans. Both are 10 hp 3-phase 240. One of them is run off a standard starter, protected by 30 amp time-delay fuses. The other runs off a drive (they had to change the fan blades a while back because the old one broke and wasn't available anymore, so they had to put one in with a more aggressive blade pitch. They put the drive in to slow it down I guess).

Anyway for no apparent reason, the motor supplied by the standard starter, started blowing its fuses. I went to check it out. Megged the branch circuit conductors to each other and to ground, and megged the motor leads. All good. Hit start and the motor started up waaaaay heavy and settled in at about 45 amps. Waaaaay high for this motor; the identical motors in other rooms pull about 15 amps. Plus it's brand new.

Then the maintenance guy came by and I suggested we remove the fan blade and run the motor with no load. So we did, and switched it in. Started up nice and easy and settled in around 10 amps per leg. Perfectly fine!

Then we reattached the fan blade and tried again. Right back to really hard starting and running way hot. Clearly it is the driven load causing the issue, but I can't imagine why. The same fan blade has been there for years and has always run normally. And it's just one big chunk of metal. No joints or rivets or adjustable blades or anything. Obviously it can't have changed its own shape.

Any ideas?
 

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Down at the fish plant they have several drive-in blast freezers. One of the smaller ones has two big evaporator fans. Both are 10 hp 3-phase 240. One of them is run off a standard starter, protected by 30 amp time-delay fuses. The other runs off a drive (they had to change the fan blades a while back because the old one broke and wasn't available anymore, so they had to put one in with a more aggressive blade pitch. They put the drive in to slow it down I guess).

Anyway for no apparent reason, the motor supplied by the standard starter, started blowing its fuses. I went to check it out. Megged the branch circuit conductors to each other and to ground, and megged the motor leads. All good. Hit start and the motor started up waaaaay heavy and settled in at about 45 amps. Waaaaay high for this motor; the identical motors in other rooms pull about 15 amps. Plus it's brand new.

Then the maintenance guy came by and I suggested we remove the fan blade and run the motor with no load. So we did, and switched it in. Started up nice and easy and settled in around 10 amps per leg. Perfectly fine!

Then we reattached the fan blade and tried again. Right back to really hard starting and running way hot. Clearly it is the driven load causing the issue, but I can't imagine why. The same fan blade has been there for years and has always run normally. And it's just one big chunk of metal. No joints or rivets or adjustable blades or anything. Obviously it can't have changed its own shape.

Any ideas?
No restrictions, ice, etc. in the evap? Otherwise I'd be suspicious of the motor. Bearings sound ok with no end play?
 

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I know you said the motors are identical but are you 100% sure it's the same RPM as the motor it replaced? Could it be the old one was 1725 and this one is 3450?

Also, did the problems start before or after the new motor?
 

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Is it possible that the fan is somehow doing more work? For instance, maybe there was a restriction on the outlet or inlet before that made it draw less current. The current in a squirrel cage motor is proportional to the amount of work it's doing, so moving more air = more work = more amps.
 

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Did you check the basics: Is motor wired correctly? Could there be a phase loss or bad starter contact. A failed termination? If this problem only appeared after the new motor installation, check the motor RPMs. If there are no electrical problems the fan is most likely moving more air for some reason.

It is always possible that a power, starter or connection problem killed the original motor and that problem still exists.
 

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When you had the fan off did you turn the shaft by hand, and lift up on it to check for undercut.
This is an interesting thought. If it's a bladed fan it will put a lot of shaft pressure opposite of the air flow. Could there be mechanical binding inside the motor?
 

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I had to read the OPs post twice.
I was kinda lead to believe that the motor with the drive was somehow affecting the other motor due to the load changing due to the new blade but, I realized that if they are evaporator fans, they just blow through coils. Not really much of a way they can work against each other unless there was some ductwork involved.
Then I saw the two words "brand new" this is the only thing that changed. Its a new motor with an unknown history at that site.
The change in load, I suspect, is a bearing or something loose causing a drag or wrong motor type.
 

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I'll vote for bearing wear. OEM fans will often be designed to the bare minimums, including non-standard motors that take cost out by using very exacting engineering of things like bearings. If the replacement blades were even a little heavier, it could have hastened the end of life. Then if you think about it, the old blades were no longer made right? That means they were either really old, or the design was so bad to begin with they just cut their losses. So an original design error may have rendered those bearings almost useless before you replaced the blades, you are just witnessing the final death throes. Fan blades break because of vibration, the vibration that caused it to break May have been the first warning sign of a failing motor bearing. The fact that you could spin it with no blades doesn't mean they were good, because without the blades there was no axial load.
 

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Besides all the things already said, you are there only to solve the problem, but didn't do the installations. Sometimes the maintenance people don't give you the whole story of what they did.

But like post #6 Varmit said "It is always possible that a power, starter or connection problem killed the original motor and that problem still exists. "
 

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Eric. Are you certain this new motor is apples to apples to the old one?
For example a 10 hp motor for a centrifuge would not work on a normal application.
All the specs would be the same except for the "Design" code. ( Limits of Torque).

If the motor is exact without any further question, you need to check every connection to this motor next. A high resistance connection will read the proper voltage, but should go to zero when a load is presented.
Bus duct stabs and sockets are bad for this as they are not normally suspected. Also breakers, starters and overload contacts.
Have you checked current during the averse condition? All three legs during start up and eventual run?

You did say fuses and not overload tripping right?

Lastly. I know you hate to do this, but if you cannot find any issue with the motor or its wiring and or connections, I would swap out a known good motor doing this exact same job if possible.
If the problem follows the motors, then its not the motor.

And make damn sure this new motor is the same as the one they took out. Check the design letter or code to see.
 

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Can you send a schematic of the circuit? I know, it may sound stupid, but one never knows.

My gut feeling is that: 1. the fan blade is either dirty, out of balanced or warped. 2. The variable drive fan motor or drive is back-feeding an inbalance to the other.

Just guesses.
 

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This may be a ways out in left field, but here goes anyway. Lol.

Are the two motors a long distance from the source, and fairly small wire?

The reason I ask is because the input to every VFD is a switching power supply, and by their very nature, they will cause distortion of the sine wave of their feeders.

Since a motor operating directly across the lines is a reactive device, it will see distorted waveforms as mostly input power, but the distortion will be seen as an opportunity to become a generator and attempt to correct the distortion.

This will cause higher current to be read and therefore, more heat in the stator.

A line reactor on the input side of the VFD will help a lot, but only if a distorted wave is the actual problem. A scope will tell you how much the VFD is screwing with the other motor.

Yes, this is a longshot at best, I seriously doubt if a distorted wave could cause the amount of current you're seeing, but if you have access to a scope, it'd be worth it to see.

The more likely possibility is, as noted, bearings. It takes very little slop in motor bearings to cause the rotor to be misaligned with the stator, and this will always result is high current and low HP. And growling, especially during starting.

Pay close attention to inward/outward play in the bearings. A 10HP fan will place roughly 30lbs. of thrust on the shaft either inward or outward, depending on the direction of airflow. If you push in or pull out the shaft with 30 lbs of force, and it moves in or out, there's your problem.
 

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Discussion Starter · #15 ·
No restrictions, ice, etc. in the evap? Otherwise I'd be suspicious of the motor. Bearings sound ok with no end play?
The motor and blades are not frozen over. Ice buildup on the evap coils would restrict air flow and reduce current flow for the motor as it is doing less work (moving less air). It is all on a periodic defrost timer cycle anyway.

I know you said the motors are identical but are you 100% sure it's the same RPM as the motor it replaced? Could it be the old one was 1725 and this one is 3450?

Also, did the problems start before or after the new motor?
Honestly I never saw the original motor. Maintenance guys noticed fuses blowing on the old motor and just replaced it with a brand new one. New one is 1725, I presume the old one was as well.

When you had the fan off did you turn the shaft by hand, and lift up on it to check for undercut.
Yes, it spins freely.

Is it possible that the fan is somehow doing more work? For instance, maybe there was a restriction on the outlet or inlet before that made it draw less current. The current in a squirrel cage motor is proportional to the amount of work it's doing, so moving more air = more work = more amps.
Hard to say. Long story short: same old fan blades on a brand new motor.

Did you check the basics: Is motor wired correctly? Could there be a phase loss or bad starter contact. A failed termination? If this problem only appeared after the new motor installation, check the motor RPMs. If there are no electrical problems the fan is most likely moving more air for some reason.

It is always possible that a power, starter or connection problem killed the original motor and that problem still exists.
Motor wired correctly. I shut it off and locked it out and went in to the freezer (f*ck that was cold), took apart the peckerhead and megged the motor right there. Also megged the conductors L-L and L-G. Put it all back together myself.

The circuit originates about 30 conductor feet away from the motor. Dead simple. Taps off a motor feeder into a fused disconnect, from there right into a starter box, and then a straight shot to the motor. No local disconnect :whistling2: no splices, straight home run.

Eric. Are you certain this new motor is apples to apples to the old one?
For example a 10 hp motor for a centrifuge would not work on a normal application.
All the specs would be the same except for the "Design" code. ( Limits of Torque).

If the motor is exact without any further question, you need to check every connection to this motor next. A high resistance connection will read the proper voltage, but should go to zero when a load is presented.
Bus duct stabs and sockets are bad for this as they are not normally suspected. Also breakers, starters and overload contacts.
Have you checked current during the averse condition? All three legs during start up and eventual run?

You did say fuses and not overload tripping right?

Lastly. I know you hate to do this, but if you cannot find any issue with the motor or its wiring and or connections, I would swap out a known good motor doing this exact same job if possible.
If the problem follows the motors, then its not the motor.

And make damn sure this new motor is the same as the one they took out. Check the design letter or code to see.
As I mentioned, I never saw the original motor. All I can assume is that the maintenance guys order motors all the time and they know what to get.

The goofiest part is that there are no overloads :blink: The starter enclosure has an external reset button like it USED to have a starter in there, but somebody took it out and replaced it with just a contactor. When I had the fan blade off and the motor was running nice and steady, I did a FOP test on the starter (well, contactor) and it measured almost as good as a brand new set of contacts. It wasn't drawing full load however. It stays on almost all the time and doesn't get very many open/close operations.

Can you send a schematic of the circuit? I know, it may sound stupid, but one never knows.

My gut feeling is that: 1. the fan blade is either dirty, out of balanced or warped. 2. The variable drive fan motor or drive is back-feeding an inbalance to the other.

Just guesses.
The drive is a separate circuit feeding a separate motor entirely. The fan blade is fine.

This may be a ways out in left field, but here goes anyway. Lol.

Are the two motors a long distance from the source, and fairly small wire?

The reason I ask is because the input to every VFD is a switching power supply, and by their very nature, they will cause distortion of the sine wave of their feeders.

Since a motor operating directly across the lines is a reactive device, it will see distorted waveforms as mostly input power, but the distortion will be seen as an opportunity to become a generator and attempt to correct the distortion.

This will cause higher current to be read and therefore, more heat in the stator.

A line reactor on the input side of the VFD will help a lot, but only if a distorted wave is the actual problem. A scope will tell you how much the VFD is screwing with the other motor.

Yes, this is a longshot at best, I seriously doubt if a distorted wave could cause the amount of current you're seeing, but if you have access to a scope, it'd be worth it to see.

The more likely possibility is, as noted, bearings. It takes very little slop in motor bearings to cause the rotor to be misaligned with the stator, and this will always result is high current and low HP. And growling, especially during starting.

Pay close attention to inward/outward play in the bearings. A 10HP fan will place roughly 30lbs. of thrust on the shaft either inward or outward, depending on the direction of airflow. If you push in or pull out the shaft with 30 lbs of force, and it moves in or out, there's your problem.
The fan on the drive is operating fine; the other non-VFD fan is the one with issues.

So sounds like the consensus is bearings huh? It's the only thing I can think of that would cause this issue. But why the hell did it start acting like this when they still had the OLD motor in place??

The overcurrent issue is steady and even on all 3 phases. There isn't one leg in particular that's over-amping. Clearly it's a load issue, which could be argued to include gnarley bearings. But really? Brand new motor, right out of the box, with sh!tty bearings?
 

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From your detailed description of the problem, I would say that the original motor failed for unknown reason(s). The new motor seems to have some internal winding problems, either some windings open or or some windings shorted (not to ground) causing, in either scenario, an increased current draw.

Just because something is new is meaningless anymore. i have "out of the box" failures all of the time.

Did you check the all three phases for proper voltage while running and off?
 

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Baldor motors are quality product, never had one fail out of the box. Years ago we were changing a 3 ph motor on top of a big oven, I tried to hand it up, should have used a boom truck, dropped it, it never did work right, kept tripping the breaker if i recall, had to end up getting another new motor. Of course, don't expect the maint guys to fess up in a hundred million years. We don't fess up to nuttin.
 

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Eric. Is the fan blade attached directly to the motor shaft or is the motor turning an assembly? Pulleys and belts?

I assumed it was direct drive, but now I am not sure. If its not direct drive, its time the mechanical aspect of this problem is addressed.
You can prove this with another motor. A swap out. If replacing the motor does no good, then for sure its a mechanical issue. And in some cases out of your hands and into the hands of the maintenance mechanics.
 

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When I worked in a meat packing plant we had to order special motors to run in our blast freezers. The freezer was kept at -40. You had to wear a cold suit to work in there. If I rememeber correctly it had something to do with the type of grease in the motor bearings. But that was over 30 years ago and I don't remember what the spec was. But I do remember ordering special motors to use in this application. I had to swap a bad one out and it took several weeks to get a replacement
 

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Discussion Starter · #20 ·
Eric. Is the fan blade attached directly to the motor shaft or is the motor turning an assembly? Pulleys and belts?

I assumed it was direct drive, but now I am not sure. If its not direct drive, its time the mechanical aspect of this problem is addressed.
You can prove this with another motor. A swap out. If replacing the motor does no good, then for sure its a mechanical issue. And in some cases out of your hands and into the hands of the maintenance mechanics.
Direct. Fan blade mounted right on the motor shaft.
 
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