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  1. #1
    Join Date
    Mar 2013
    Location
    Va
    Posts
    49

    Over amperage on cook return fan

    Ive got a 1.5 hp 1750 rpm 460 volt return fan motor that has been giving me issues overamping for the last 2 months. The freq drive is tripping on calculated motor temp. Basically it monitors the motors amperage and bases that on motor temperature. The nameplate states that at 460 volt the motor should pull 2.2 amps. The motor is pulling 3 to 3.5 amps. I replaced it with a weg motor with the same nameplate data. New motor is doing the same thing. Ive checked all my connections, looked at the contacts on the contactor. Everything looks good. I even bypassed the drive itself by running temporary wires directly from the disconnect to the motor. Same problem. The fan spins freely, as free as the identical one located in the same mech room which is running normal at 1.8 amps. The belt is snug like it should be. Remove the belt and the motor pulls .8 amps. My voltage looks good at 492 across all three legs. Something has changed in the last 2 months that is now causing this problem. Any ideas?

  2. #2
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,563
    I'm not sure about what a "weg" motor is.

    Are we talking single phase?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #3
    Join Date
    Mar 2013
    Location
    Va
    Posts
    49
    3 phase. Weg is the motor manufacturer. http://www.weg.net/us. Hopefully links are allowed.

  4. #4
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,563
    Are current readings being taken at the VFD or at the motor?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  5. #5
    Join Date
    Mar 2013
    Location
    Va
    Posts
    49
    At disconnect, drive, and motor.

  6. #6
    Join Date
    Aug 2007
    Location
    Southern,Ca
    Posts
    544
    is there a restriction in the ductwork? is this a grease hood are there grease filters that are plugged up

  7. #7
    Join Date
    Dec 2003
    Posts
    2,411
    The fan is moving more air if its pulling more amps. What could have changed to put less resistance on the fan and let it move more air? Thats what you need to be thinking about. Cant you do something in the drive to limit the speed to keep it from tripping?

  8. #8
    Join Date
    Aug 2007
    Location
    Southern,Ca
    Posts
    544
    Quote Originally Posted by bigtime View Post
    The fan is moving more air if its pulling more amps. What could have changed to put less resistance on the fan and let it move more air? Thats what you need to be thinking about. Cant you do something in the drive to limit the speed to keep it from tripping?
    Good point. With that said it is possible that an access door has either fallen off or been left off by the grease guys. That is if it is a grease hood



    Sent from my SCH-I535 using Tapatalk 2

  9. #9
    Join Date
    Jun 2012
    Location
    East tx
    Posts
    164
    Adjustable pulleys?

  10. #10
    Join Date
    Aug 2007
    Location
    Southern,Ca
    Posts
    544
    Quote Originally Posted by Crazecodyk View Post
    Adjustable pulleys?
    Most of the vfd exhausts I've seen are direct drive but I guess we will have to wait until he answeres

    Sent from my SCH-I535 using Tapatalk 2

  11. #11
    Join Date
    Aug 2007
    Location
    Southern,Ca
    Posts
    544
    Another possibility is that they changed the grease filters to a less restrictive style and that vfd was set spot on for the amperage than the filters were changed and it was now overamping! But again that is only if there are filters

    Sent from my SCH-I535 using Tapatalk 2

  12. #12
    Join Date
    Mar 2013
    Location
    Va
    Posts
    49
    This is a return fan not an exhaust fan. There werent any access doors or anything of the like i can find left open. This problem started about 2 months ago. I also have 3 other ex fans on the roof pulling higher then normal amps. Ive had the power company check there incoming power from there transformer. They say everything looks good on there end? The only maintenance that was done now that i think about it was a filter change. Prefilters and Finals. But ive totally removed dirty filters temporarily in the past till the new ones arrived because of low static pressure. Never had any problems like this.
    Last edited by Onefast450r; 05-17-2013 at 10:40 PM. Reason: Mistake

  13. #13
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,563
    Quote Originally Posted by Onefast450r View Post
    This is a return fan not an exhaust fan. There werent any access doors or anything of the like i can find left open. This problem started about 2 months ago. I also have 3 other ex fans on the roof pulling higher then normal amps. Ive had the power company check there incoming power from there transformer. They say everything looks good on there end? The only maintenance that was done now that i think about it was a filter change. Prefilters and Finals. But ive totally removed dirty filters temporarily in the past till the new ones arrived because of low static pressure. Never had any problems like this.
    Maybe I just don't do enough restaurant work, but I'm not sure what you mean by a "return fan." Do you by any chance mean makeup air unit?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







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