Motor troubleshooting help

[Besoeker]

OP stated his responsibility was only to check premises wiring. There was a service professional on site for the compressor.

I’d guess he passed on the recommendation to him/her.

Yes, but the OP's point remains - why the reluctance to change the motor? That could/probably would bottom out the issue at a stroke. Healthy motors do not take such unbalanced currents.

 

[Cow]

Yes, but the OP's point remains - why the reluctance to change the motor? That could/probably would bottom out the issue at a stroke. Healthy motors do not take such unbalanced currents.

Since you're in the UK you may not have heard this expression: "you can lead a horse to water, but you can't make him drink."

 

[kwired]

OP stated his responsibility was only to check premises wiring. There was a service professional on site for the compressor.

I’d guess he passed on the recommendation to him/her.

Those compressor guys don't always understand motors. But if he was told the premises wiring was fine then he needs to concede that it may be the motor.

Maybe put an alternate load on same circuit to prove premises wiring is fine?

Healthy motors do not take such unbalanced currents.

:thumbsup:

 

[Besoeker]

Since you're in the UK you may not have heard this expression: "you can lead a horse to water, but you can't make him drink."

I think it came from here and the modern version is attributed to Frederick Marryat.

 

[jimo144]

Motor troubleshooting help

To me it seems that it is obvious that the problem is in the motor but for some reason the engineers keep looking to the premise wiring as the culprit. What am I missing?

There is another line of thought for the Cause. An Air Compressor is designed to have a Check Valve that allows Flo towards the Reservoir and blocks that air from coming back to the Compressor. Compressors also may have an Unloader Valve that lets the Compressor Spin Up without a load then start pumping once the run full RPM has been reached. Another form is a Check Valve and a Drain Valve that drains the compressed air between the Compressor and the Check Valve so again, the Compressor can Spin Up without load.
If any or all of the Unloading techniques fails, the Motor is trying to start under load and will Trip something or burn the Motor out. If the problem is intermittent, maybe a video camera can watch the Compressor until it Trips. Have the Camera watch the Pulley / Flywheel so you can tell if the Motor is starting under load. It will be obvious, the Motor will try; may even be able to start spinning the Compressor slowly but will trip after a few Seconds.

 

[kwired]

There is another line of thought for the Cause. An Air Compressor is designed to have a Check Valve that allows Flo towards the Reservoir and blocks that air from coming back to the Compressor. Compressors also may have an Unloader Valve that lets the Compressor Spin Up without a load then start pumping once the run full RPM has been reached. Another form is a Check Valve and a Drain Valve that drains the compressed air between the Compressor and the Check Valve so again, the Compressor can Spin Up without load.
If any or all of the Unloading techniques fails, the Motor is trying to start under load and will Trip something or burn the Motor out. If the problem is intermittent, maybe a video camera can watch the Compressor until it Trips. Have the Camera watch the Pulley / Flywheel so you can tell if the Motor is starting under load. It will be obvious, the Motor will try; may even be able to start spinning the Compressor slowly but will trip after a few Seconds.

Motors can take this overloading to a certain extent, as long as proper overload protection shuts them down when it happens.

If this is something that happens frequently it does take a toll on the motor though. The need to reset it frequently should be a clue there is a problem. If it for some reason automatically resets - that can be pretty hard on the motor though, as it never really cools much before it is put into same stress again.

 

[Besoeker]

There is another line of thought for the Cause. An Air Compressor is designed to have a Check Valve that allows Flo towards the Reservoir and blocks that air from coming back to the Compressor. Compressors also may have an Unloader Valve that lets the Compressor Spin Up without a load then start pumping once the run full RPM has been reached. Another form is a Check Valve and a Drain Valve that drains the compressed air between the Compressor and the Check Valve so again, the Compressor can Spin Up without load.
If any or all of the Unloading techniques fails, the Motor is trying to start under load and will Trip something or burn the Motor out. If the problem is intermittent, maybe a video camera can watch the Compressor until it Trips. Have the Camera watch the Pulley / Flywheel so you can tell if the Motor is starting under load. It will be obvious, the Motor will try; may even be able to start spinning the Compressor slowly but will trip after a few Seconds.

Yes, no argument that this could cause overloading but it doesn't account for the unbalance. That's a motor issue.

 

[kwired]

Motors can take this overloading to a certain extent, as long as proper overload protection shuts them down when it happens.

If this is something that happens frequently it does take a toll on the motor though. The need to reset it frequently should be a clue there is a problem. If it for some reason automatically resets - that can be pretty hard on the motor though, as it never really cools much before it is put into same stress again.

Yes, no argument that this could cause overloading but it doesn't account for the unbalance. That's a motor issue.

To add more to what I said before and sort of was part of what I was thinking when I said that - repeated overloading could certainly have contributed to degrading of windings and now there is unbalanced current as a result. If left long enough you probably eventually have a failure that essentially makes it completely inoperable.

 

[retirede]

I was an EE at a compressor manufacturer for many years and provided tech support to field technicians. They are all mechanics who have limited understanding of things electrical.
When they see things like current imbalance, they will likely need guidance. That is what the OP was trying to provide.
The technician’s lack of electrical understanding also explains the reluctance to accept the advice of the OP. The first tendency is to point the finger at somebody else’s stuff.
I’m not disagreeing with most of what you guys are saying, just trying to explain things from the point of view of somebody who’s lived these situations.
I do disagree with those who say this is caused by a compressor mechanical issue.

 

[kwired]

I was an EE at a compressor manufacturer for many years and provided tech support to field technicians. They are all mechanics who have limited understanding of things electrical.
When they see things like current imbalance, they will likely need guidance. That is what the OP was trying to provide.
The technician’s lack of electrical understanding also explains the reluctance to accept the advice of the OP. The first tendency is to point the finger at somebody else’s stuff.
I’m not disagreeing with most of what you guys are saying, just trying to explain things from the point of view of somebody who’s lived these situations.
I do disagree with those who say this is caused by a compressor mechanical issue.

I will agree that a mechanical issue is not a direct relation to unbalanced current.

I don't necessarily rule out a mechanical issue being the root of what happened, continued overloading because of a mechanical issue could eventually have compromised motor windings leading to the unbalanced current.

 

[retirede]

I will agree that a mechanical issue is not a direct relation to unbalanced current.

I don't necessarily rule out a mechanical issue being the root of what happened, continued overloading because of a mechanical issue could eventually have compromised motor windings leading to the unbalanced current.

True, I’ll also tell you that most industrial compressors that use NEMA motors are designed to use 10% of the 15% service factor when fully loaded.

Motor life can be shortened significantly, especially in cases where the supply voltage is slightly low and/or imbalanced.

They do tend to survive the warranty period.

 

[Besoeker]

To add more to what I said before and sort of was part of what I was thinking when I said that - repeated overloading could certainly have contributed to degrading of windings and now there is unbalanced current as a result. If left long enough you probably eventually have a failure that essentially makes it completely inoperable.

Yes, there's no doubt repeated overloading could have damaged the motor. That would still require the motor to be replaced. There may be other problems that require further steps to be taken.