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Thread: Two speed one winding motor troubleshooting advice

  1. #11
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    Quote Originally Posted by phineascage View Post
    I have not checked this yet but have this on the list to do when the opportunity comes. Right now I do know that the our problem fan motor is drawing about 45A greater while coupled to it's gearbox than either one of our other fan motors in High that are both operating normally.
    gearbox issue???
    Bob

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    Quote Originally Posted by petersonra View Post
    gearbox issue???
    Possible but would the motor shop have had the gearbox?
    Their measured 152A just doesn't seem right for that motor off load.
    Si hoc legere scis nimium eruditionis habes.

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    Quote Originally Posted by Besoeker View Post
    It might be instructive to see what they all do uncoupled to anything. That would quickly clue you into whether the issue is mechanical or electrical.
    I know it isn't always easy to replicate seemingly simple tests on site But, if you want to bottom out the current disparities, you/your customer may have to bite the bullet.
    I appreciate the advice. Unfortunately that isn't feasible at this current time. We need all three of our cooling tower fan motors running in high now due to ambient temperatures and we're running our problem fan in Low right now to, hopefully, save what life it has during the extreme hot months of summer. I am right now trying to gather as many ideas as possible to execute should we have an unlikely shutdown during summer or when we can live with 1 fan in High operation during next Fall/Winter.

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    Quote Originally Posted by petersonra View Post
    gearbox issue???
    Certainly a possibility except at our site connected to our feed with no load attached we draw higher current than what the motor shop recorded at their site and their feed.

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    Quote Originally Posted by Besoeker View Post
    Possible but would the motor shop have had the gearbox?
    Their measured 152A just doesn't seem right for that motor off load.
    No they did not have the gear box. They ran the motor uncoupled to anything.

  6. #16
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    Quote Originally Posted by phineascage View Post
    I appreciate the advice. Unfortunately that isn't feasible at this current time. We need all three of our cooling tower fan motors running in high now due to ambient temperatures and we're running our problem fan in Low right now to, hopefully, save what life it has during the extreme hot months of summer. I am right now trying to gather as many ideas as possible to execute should we have an unlikely shutdown during summer or when we can live with 1 fan in High operation during next Fall/Winter.
    Understood. I've been there in the industrial field. Output takes overwhelming priority.
    Si hoc legere scis nimium eruditionis habes.

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    High efficiency motors, as many cooling towers started using a long time ago, tend to have very very poor power factor when uncoupled, so the 152A actually doesn't sound that unusual. If measured with a proper power meter, you would likely see that was at a .2 power factor, maybe less. The motor design is optimized to run efficiently at full load but drops precipitously as load sheds, because on a centrifugal load like that motor efficiency at low speed becomes irrelevant since the nature of the LOAD is such that at low speed, the power required by the fan is reduced by the cube of the speed change.

    All that said, a gearbox adding >20% load even unloaded does sound like a mechanical issue.
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    Quote Originally Posted by Jraef View Post
    High efficiency motors, as many cooling towers started using a long time ago, tend to have very very poor power factor when uncoupled, so the 152A actually doesn't sound that unusual.
    My experience suggests otherwise. The 152A is almost 62% of FLC.
    Have you seen that in real life?
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    Quote Originally Posted by Jraef View Post
    High efficiency motors, as many cooling towers started using a long time ago, tend to have very very poor power factor when uncoupled, so the 152A actually doesn't sound that unusual. If measured with a proper power meter, you would likely see that was at a .2 power factor, maybe less. The motor design is optimized to run efficiently at full load but drops precipitously as load sheds, because on a centrifugal load like that motor efficiency at low speed becomes irrelevant since the nature of the LOAD is such that at low speed, the power required by the fan is reduced by the cube of the speed change.

    All that said, a gearbox adding >20% load even unloaded does sound like a mechanical issue.
    I believe I have misspoke. When I said "unloaded", I meant not connected to any load or more correctly uncoupled. So when the motor was ran at the motor shop it was uncoupled and drew 152A in High speed. At our site, uncoupled the motor drew about 197A, roughly 45A greater than seen at the motor shop. When the motor was coupled to the gear box at our site and run in High, it drew roughly 327A compared to another normally functioning motor that drew roughly 282A while running in High, again about 45A higher.

  10. #20
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    Quote Originally Posted by Besoeker View Post
    My experience suggests otherwise. The 152A is almost 62% of FLC.
    Have you seen that in real life?
    Yes, on 2S1W cooling tower fans in particular. Extremely low PF when uncoupled in high speed, in the order of .20 or less. So most of that current is reactive.

    The 45A difference when coupled to the gearbox is, in my opinion, the most suspicious aspect. As a general rule the most common gearboxes (Marley and Amarillo) are roughly 90% efficient. 45A out of 197A represents about 22% losses. A properly functioning gearbox would not be that much less efficient.
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